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BACKGROUND: BPDCN is a rare, aggressive hematologic malignancy characterized by historically poor overall survival and limited therapeutic options. Despite the recent approval of tagraxofusp-erzs for BPDCN, outcomes remain suboptimal for many patients. Additionally, patients with BPDCN are older and often have co-morbidities at baseline, preventing them from receiving tagraxofusp-erzs. Therefore, novel therapies are needed in the frontline setting for patients with BPDCN. Overexpression of CD123 (IL-3Rα) is present in all BPDCN cases, thereby establishing this surface marker as a target for therapeutic intervention. IMGN632 is a CD123-targeting ADC, comprised of a high-affinity anti-CD123 antibody coupled to a DNA-alkylating payload of the novel IGN (indolinobenzodiazepine pseudodimer) class. IMGN632 has demonstrated favorable safety and promising clinical activity in relapsed/refractory (R/R) BPDCN [Blood (2020) 136 (Supplement 1): 11-13], leading to the FDA granting IMGN632 Breakthrough Therapy Designation (BTD) for R/R BPDCN (Oct 2020). Following BTD and alignment with FDA, a pivotal cohort in frontline (no prior systemic treatment) BPDCN patients was initiated in addition to a continuing cohort of patients with R/R disease, where we have enrolled 33 patients to date. Here we report the initial experience of three frontline patients who are not part of the pivotal cohort. METHODS: IMGN632 was administered IV at a dose of 0.045 mg/kg on day 1 of a 21-day cycle to all patients. Efficacy was assessed using modified Severity Weighted Assessment Tool (for skin lesions), PET/CT, and blast percentage in bone marrow aspirates. The response criteria were adapted from established BPDCN criteria (Pemmaraju NEJM 2019). RESULTS: Three patients with frontline BPDCN (no prior systemic therapy) received IMGN632. All three of these frontline patients achieved a clinical complete remission (CRc). Patient 1 was a 79yo woman who presented with skin, nodal, and extensive bone marrow disease (80% involvement). After one dose of IMGN632, she cleared her bone marrow (0%), and after 3 cycles, her nodal lesions and skin lesions resolved to achieve a CRc. Upon complete response, treatment was held due to patient co-morbidities. With just 3 cycles of IMGN632, this patient achieved duration of response (DOR) of 10.7 months without further therapy. Patient 2 was a 67yo man who had extensive skin disease covering >20% of the body; over several cycles, he achieved a PR then a CRc and bridged to an allogeneic stem cell transplant (SCT). The patient achieved a DOR of 13.5 months, with no evidence of disease relapse when he died from graft versus host disease. Patient 3 was a 66yo woman who presented with extensive skin and nodal lesions. After improvement over 4 cycles, she achieved a CRc with clearing of most of her skin lesions and all nodal lesions. Unfortunately, while still in CRc, the patient died of COVID-19 pneumonia, with a DOR of 3.7 months. CONCLUSION: Administration of IMGN632 to frontline BPDCN patients resulted in clinical complete remission in the initial three patients with durable responses in the two non-COVID impacted patients. None of these patients progressed while on therapy, and one patient successfully bridged to SCT. Enrollment continues in the pivotal frontline and R/R cohorts. (BPDCNtrial.com; NCT03386513). Disclosures Pemmaraju: Sager Strong Foundation: Other; Daiichi Sankyo, Inc.: Other, Research Funding; Aptitude Health: Consultancy; ASH Communications Committee: Membership on an entity's Board of Directors or advisory committees; Affymetrix: Consultancy, Research Funding; HemOnc Times/Oncology Times: Membership on an entity's Board of Directors or advisory committees; ASCO Leukemia Advisory Panel: Membership on an entity's Board of Directors or advisory committees; Dan's House of Hope: Membership on an entity's Board of Directors or advisory committees; Samus: Other, Research Funding; Springer Science + Business Media: Other; DAVA Oncology: Consultancy; Plexxicon: Other, Research Funding; Cellectis S.A. ADR: Other, Research Funding; Protagonist Therapeutics, Inc.: Consultancy; CareDx, Inc.: Consultancy; Novartis Pharmaceuticals: Consultancy, Other: Research Support, Research Funding; Clearview Healthcare Partners: Consultancy; Blueprint Medicines: Consultancy; Incyte: Consultancy; LFB Biotechnologies: Consultancy; Roche Diagnostics: Consultancy; MustangBio: Consultancy, Other; Abbvie Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding; Celgene Corporation: Consultancy; Stemline Therapeutics, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding; Bristol-Myers Squibb Co.: Consultancy; ImmunoGen, Inc: Consultancy; Pacylex Pharmaceuticals: Consultancy. Martinelli: Incyte: Consultancy; Daichii Sankyo: Consultancy; Jazz Pharmaceuticals: Consultancy; Astellas: Consultancy, Speakers Bureau; Abbvie: Consultancy; Roche: Consultancy; Pfizer: Consultancy, Speakers Bureau; Stemline Therapeutics: Consultancy; Celgene /BMS: Consultancy, Speakers Bureau. Lane: Qiagen: Consultancy, Honoraria; N-of-One: Consultancy, Honoraria; Stemline Therapeutics: Research Funding; AbbVie: Research Funding. Deconinck: Imunogen: Membership on an entity's Board of Directors or advisory committees; Stemline Therapetutics: Membership on an entity's Board of Directors or advisory committees; Chugai: Research Funding; Novartis: Research Funding; Pfizer: Other: Travel Grants, Research Funding; Abbevie: Research Funding. Wang: Jazz Pharmaceuticals: Consultancy, Honoraria, Other: Advisory Board; Kite Pharmaceuticals: Consultancy, Honoraria, Other: Advisory Board; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Other: Advisory Board; Kura Oncology: Consultancy, Honoraria, Other: Advisory board, steering committee, Speakers Bureau; BMS/Celgene: Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Consultancy, Honoraria, Other: Advisory Board; Genentech: Membership on an entity's Board of Directors or advisory committees; Mana Therapeutics: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria, Other: Advisory Board, Speakers Bureau; Stemline Therapeutics: Consultancy, Honoraria, Other: Advisory board, Speakers Bureau; Takeda: Consultancy, Honoraria, Other: Advisory board; DAVA Oncology: Consultancy, Speakers Bureau; Rafael Pharmaceuticals: Other: Data safety monitoring committee; Gilead: Consultancy, Honoraria, Other: Advisory board; Daiichi Sankyo: Consultancy, Honoraria, Other: Advisory board; PTC Therapeutics: Consultancy, Honoraria, Other: Advisory board; Genentech: Consultancy; MacroGenics: Consultancy. Sweet: Bristol Meyers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; AROG: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. Rizzieri: AbbVie: Membership on an entity's Board of Directors or advisory committees; AROG: Membership on an entity's Board of Directors or advisory committees; Bayer: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Teva: Membership on an entity's Board of Directors or advisory committees; Acrotech: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Stemline: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Kite: Honoraria, Speakers Bureau; Karyopharm: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees; Celltrion: Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Mustang: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Jazz: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Honoraria; Pharmacyclics: Honoraria. DeAngelo: Shire: Consultancy; Takeda: Consultancy; Abbvie: Research Funding; Novartis: Consultancy, Research Funding; GlycoMimetics: Research Funding; Agios: Consultancy; Blueprint Medicines Corporation: Consultancy; Amgen: Consultancy; Pfizer: Consultancy; Incyte Corporation: Consultancy; Jazz: Consultancy; Forty-Seven: Consultancy; Autolus: Consultancy. Montesinos: Karyopharm: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Sanofi: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Forma Therapeutics: Consultancy; Stemline/Menarini: Consultancy; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Teva: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Glycomimetics: Consultancy; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Daiichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Tolero Pharmaceutical: Consultancy; Agios: Consultancy; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Astellas Pharma, Inc.: Consultancy, Honoraria, Other: Advisory board, Research Funding, Speakers Bureau. Erba: AbbVie Inc; Agios Pharmaceuticals Inc; Astellas; Bristol Myers Squibb; Celgene, a Bristol Myers Squibb company; Daiichi Sankyo Inc; Genentech, a member of the Roche Group; GlycoMimetics Inc; Incyte Corporation; Jazz Pharmaceuticals Inc; Kura Oncology; Nov: Other: Advisory Committee; AbbVie Inc; Agios Pharmaceuticals Inc; Bristol Myers Squibb; Celgene, a Bristol Myers Squibb company; Incyte Corporation; Jazz Pharmaceuticals Inc; Novartis: Speakers Bureau; AbbVie Inc: Other: Independent review committee; AbbVie Inc; Agios Pharmaceuticals Inc; ALX Oncology; Amgen Inc; Daiichi Sankyo Inc; FORMA Therapeutics; Forty Seven Inc; Gilead Sciences Inc; GlycoMimetics Inc; ImmunoGen Inc; Jazz Pharmaceuticals Inc; MacroGenics Inc; Novartis; PTC Therapeutics: Research Funding. Konopleva: Ascentage: Other: grant support, Research Funding; Sanofi: Other: grant support, Research Funding; Stemline Therapeutics: Research Funding; AbbVie: Consultancy, Honoraria, Other: Grant Support, Research Funding; Genentech: Consultancy, Honoraria, Other: grant support, Research Funding; Forty Seven: Other: grant support, Research Funding; Agios: Other: grant support, Research Funding; KisoJi: Research Funding; Rafael Pharmaceuticals: Other: grant support, Research Funding; AstraZeneca: Other: grant support, Research Funding; Eli Lilly: Patents & Royalties: intellectual property rights, Research Funding; Calithera: Other: grant support, Research Funding; Cellectis: Other: grant support; Ablynx: Other: grant support, Research Funding; Novartis: Other: research funding pending, Patents & Royalties: intellectual property rights; Reata Pharmaceuticals: Current holder of stock options in a privately-held company, Patents & Royalties: intellectual property rights; F. Hoffmann-La Roche: Consultancy, Honoraria, Other: grant support. Kantarjian: Novartis: Honoraria, Research Funding; Jazz: Research Funding; Daiichi-Sankyo: Research Funding; Pfizer: Honoraria, Research Funding; KAHR Medical Ltd: Honoraria; Astellas Health: Honoraria; Astra Zeneca: Honoraria; NOVA Research: Honoraria; Aptitude Health: Honoraria; Immunogen: Research Funding; Ipsen Pharmaceuticals: Honoraria; BMS: Research Funding; Ascentage: Research Funding; Amgen: Honoraria, Research Funding; AbbVie: Honoraria, Research Funding; Precision Biosciences: Honoraria; Taiho Pharmaceutical Canada: Honoraria. Walter: Agios Pharmaceuticals, Inc.: Consultancy, Research Funding; Amgen, Inc.: Consultancy, Research Funding; Amphivena Therapeutics, Inc.: Current equity holder in publicly-traded company; Aptevo Therapeutics, Inc.: Consultancy, Research Funding; Arog Pharmaceuticals, Inc.: Research Funding; Astellas Pharma US, Inc.: Consultancy; BioLineRx, Ltd.: Consultancy, Research Funding; Boston Biomedical, Inc.: Consultancy; Bristol Myers Squibb, Inc.: Consultancy; Celgene, Inc.: Consultancy, Research Funding; Genentech, Inc.: Consultancy; GlaxoSmithKline, Inc.: Consultancy; ImmunoGen, Inc.: Research Funding; Janssen Global Services, LLC: Consultancy; Janssen Research & Development, Inc.: Research Funding; Jazz Pharmaceuticals, Inc.: Consultancy, Research Funding; Kite Pharma, Inc.: Consultancy; Kronos Bio, Inc.: Consultancy; Kura Oncology, Inc.: Research Funding; Macrogenics, Inc.: Research Funding; New Link Genetics: Consultancy; Pfizer, Inc.: Consultancy, Research Funding; Race Oncology Ltd.: Consultancy; Selvita: Research Funding; Stemline Therapeutics, Inc.: Research Funding. Aribi: Seagen: Consultancy. Levy: Beigene: Consultancy, Honoraria, Speakers Bureau; Bristol Myers Squibb: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; TG Therapeutics: Consultancy, Honoraria, Speakers Bureau; Gilead Sciences, Inc.: Consultancy, Honoraria, Speakers Bureau; Janssen Pharmaceuticals: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; Morphosys: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; Seattle Genetics: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; Jazz Pharmaceuticals: Consultancy, Honoraria, Speakers Bureau; Dova: Consultancy, Other: Promotional speaker; AstraZeneca: Consultancy, Honoraria, Speakers Bureau; GSK: Consultancy, Other: Promotional speaker; Karyopharm: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; Epizyme: Consultancy, Other: Promotional speaker; Takeda: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; Amgen Inc.: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; AbbVie: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; Novartis: Consultancy, Other: Promotional speaker. Malcolm: Immunogen: Current Employment. Zweidler-McKay: ImmunoGen: Current Employment. Daver: Astellas: Consultancy, Research Funding; Trovagene: Consultancy, Research Funding; Sevier: Consultancy, Research Funding; Novartis: Consultancy; Bristol Myers Squibb: Consultancy, Research Funding; Gilead Sciences, Inc.: Consultancy, Research Funding; Genentech: Consultancy, Research Funding; Novimmune: Research Funding; FATE Therapeutics: Research Funding; ImmunoGen: Consultancy, Research Funding; Hanmi: Research Funding; Pfizer: Consultancy, Research Funding; Trillium: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Glycomimetics: Research Funding; Abbvie: Consultancy, Research Funding; Daiichi Sankyo: Consultancy, Research Funding; Jazz Pharmaceuticals: Consultancy, Other: Data Monitoring Committee member; Dava Oncology (Arog): Consultancy; Celgene: Consultancy; Syndax: Consultancy; Shattuck Labs: Consultancy; Agios: Consultancy; Kite Pharmaceuticals: Consultancy; SOBI: Consultancy; STAR Therapeutics: Consultancy; Karyopharm: Research Funding; Newave: Research Funding.

Background: Overexpression of CD123 (IL-3Rα receptor) is a hallmark of blastic plasmacytoid dendritic cell neoplasm (BPDCN), thus making this antigen an attractive target for the development of new therapeutics. IMGN632 is a CD123-targeting antibody-drug conjugate (ADC) comprising a novel anti-CD123 antibody coupled, via a highly-stable peptide linker, to a unique DNA-alkylating cytotoxic payload of the recently developed IGN (indolinobenzodiazepine pseudodimer) class. Preclinically, IMGN632 has demonstrated potent activity against BPDCN cells with remarkable sensitivity of patient derived xenografts to IMGN632 (Blood 2018 132:3956). IMGN632 has demonstrated a wide therapeutic index in vitro and in vivo (PMIDs: 29661755, 30361418). Importantly IMGN632 has demonstrated favorable safety profile and has demonstrated evidence of promising efficacy in patients with BPDCN (ASH 2020: Blood 2020, vol 136, suppl 1, 11-13) and AML (ASH 2019: Blood 2019, vol 134, suppl 1, 734). Based on this data, IMGN632 was granted FDA Breakthrough Therapy Designation for BPDCN (Oct 2020). Initial experience with 3 frontline BPDCN patients showed clinical complete remissions (CRc) in all three patients. Subsequently an FDA-aligned pivotal cohort enrolling frontline BPDCN patients has been added to this study. Methods: This study is currently enrolling two expansion cohorts for adults with CD123 positive BPDCN. The pivotal cohort is enrolling patients with frontline/untreated (no prior systemic therapy) BPDCN who do not have CNS involvement and meet other basic eligibility. This cohort is designed to support an application for FDA approval for IMGN632 in patients with BPDCN. An additional cohort is enrolling patients with relapsed/refractory BPDCN, which may have had up to 3 prior lines of therapy, including CD123-targeted therapies and prior hematopoietic stem cell transplant (after 120 days) and may have CNS involvement (if cleared with intrathecals), but who must not have prior history of veno-occlusive disease of the liver, or history of grade 4 capillary leak syndrome or non-cardiac grade 4 edema, and other eligibility. Both cohorts are enrolling patients at the RP2D (0.045 mg/kg IV Q 3 weeks) in the US and EU (NCT03386513, https://BPDCNtrial.com). Disclosures Pemmaraju: Clearview Healthcare Partners: Consultancy; Cellectis S.A. ADR: Other, Research Funding; Novartis Pharmaceuticals: Consultancy, Other: Research Support, Research Funding; Protagonist Therapeutics, Inc.: Consultancy; Celgene Corporation: Consultancy; MustangBio: Consultancy, Other; Plexxicon: Other, Research Funding; Blueprint Medicines: Consultancy; Dan's House of Hope: Membership on an entity's Board of Directors or advisory committees; Abbvie Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding; Affymetrix: Consultancy, Research Funding; ASCO Leukemia Advisory Panel: Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy; Daiichi Sankyo, Inc.: Other, Research Funding; Roche Diagnostics: Consultancy; DAVA Oncology: Consultancy; Aptitude Health: Consultancy; CareDx, Inc.: Consultancy; HemOnc Times/Oncology Times: Membership on an entity's Board of Directors or advisory committees; Stemline Therapeutics, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding; Springer Science + Business Media: Other; Sager Strong Foundation: Other; ASH Communications Committee: Membership on an entity's Board of Directors or advisory committees; LFB Biotechnologies: Consultancy; Bristol-Myers Squibb Co.: Consultancy; Samus: Other, Research Funding; ImmunoGen, Inc: Consultancy; Pacylex Pharmaceuticals: Consultancy. Montesinos: Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Tolero Pharmaceutical: Consultancy; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Forma Therapeutics: Consultancy; Karyopharm: Membership on an entity's Board of Directors or advisory committees, Research Funding; Stemline/Menarini: Consultancy; Sanofi: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Teva: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Glycomimetics: Consultancy; Daiichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Agios: Consultancy; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Astellas Pharma, Inc.: Consultancy, Honoraria, Other: Advisory board, Research Funding, Speakers Bureau. Lane: Qiagen: Consultancy, Honoraria; N-of-One: Consultancy, Honoraria; Stemline Therapeutics: Research Funding; AbbVie: Research Funding. Sweet: AROG: Membership on an entity's Board of Directors or advisory committees; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol Meyers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees. Wang: Kite Pharmaceuticals: Consultancy, Honoraria, Other: Advisory Board; Mana Therapeutics: Consultancy, Honoraria; Kura Oncology: Consultancy, Honoraria, Other: Advisory board, steering committee, Speakers Bureau; Stemline Therapeutics: Consultancy, Honoraria, Other: Advisory board, Speakers Bureau; Pfizer: Consultancy, Honoraria, Other: Advisory Board, Speakers Bureau; DAVA Oncology: Consultancy, Speakers Bureau; GlaxoSmithKline: Consultancy, Honoraria, Other: Advisory Board; Genentech: Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees; BMS/Celgene: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Consultancy, Honoraria, Other: Advisory Board; Novartis: Consultancy, Honoraria, Other: Advisory Board; Takeda: Consultancy, Honoraria, Other: Advisory board; Rafael Pharmaceuticals: Other: Data safety monitoring committee; Gilead: Consultancy, Honoraria, Other: Advisory board; Daiichi Sankyo: Consultancy, Honoraria, Other: Advisory board; PTC Therapeutics: Consultancy, Honoraria, Other: Advisory board; Genentech: Consultancy; MacroGenics: Consultancy. Deconinck: Imunogen: Membership on an entity's Board of Directors or advisory committees; Stemline Therapetutics: Membership on an entity's Board of Directors or advisory committees; Chugai: Research Funding; Novartis: Research Funding; Pfizer: Other: Travel Grants, Research Funding; Abbevie: Research Funding. Rizzieri: AbbVie: Membership on an entity's Board of Directors or advisory committees; AROG: Membership on an entity's Board of Directors or advisory committees; Bayer: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Teva: Membership on an entity's Board of Directors or advisory committees; Acrotech: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Stemline: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Kite: Honoraria, Speakers Bureau; Karyopharm: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees; Celltrion: Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Mustang: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Jazz: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Honoraria; Pharmacyclics: Honoraria. Walter: Agios Pharmaceuticals, Inc.: Consultancy, Research Funding; Amgen, Inc.: Consultancy, Research Funding; Amphivena Therapeutics, Inc.: Current equity holder in publicly-traded company; Aptevo Therapeutics, Inc.: Consultancy, Research Funding; Arog Pharmaceuticals, Inc.: Research Funding; Astellas Pharma US, Inc.: Consultancy; BioLineRx, Ltd.: Consultancy, Research Funding; Boston Biomedical, Inc.: Consultancy; Bristol Myers Squibb, Inc.: Consultancy; Celgene, Inc.: Consultancy, Research Funding; Genentech, Inc.: Consultancy; GlaxoSmithKline, Inc.: Consultancy; ImmunoGen, Inc.: Research Funding; Janssen Global Services, LLC: Consultancy; Janssen Research & Development, Inc.: Research Funding; Jazz Pharmaceuticals, Inc.: Consultancy, Research Funding; Kite Pharma, Inc.: Consultancy; Kronos Bio, Inc.: Consultancy; Kura Oncology, Inc.: Research Funding; Macrogenics, Inc.: Research Funding; New Link Genetics: Consultancy; Pfizer, Inc.: Consultancy, Research Funding; Race Oncology Ltd.: Consultancy; Selvita: Research Funding; Stemline Therapeutics, Inc.: Research Funding. Aribi: Seagen: Consultancy. Levy: Bristol Myers Squibb: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; Amgen Inc.: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; Janssen Pharmaceuticals: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; Takeda: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; Beigene: Consultancy, Honoraria, Speakers Bureau; Novartis: Consultancy, Other: Promotional speaker; AstraZeneca: Consultancy, Honoraria, Speakers Bureau; Jazz Pharmaceuticals: Consultancy, Honoraria, Speakers Bureau; Morphosys: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; Seattle Genetics: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; Karyopharm: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; GSK: Consultancy, Other: Promotional speaker; TG Therapeutics: Consultancy, Honoraria, Speakers Bureau; Gilead Sciences, Inc.: Consultancy, Honoraria, Speakers Bureau; Epizyme: Consultancy, Other: Promotional speaker; AbbVie: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; Dova: Consultancy, Other: Promotional speaker. Martinelli: Pfizer: Consultancy, Speakers Bureau; Stemline Therapeutics: Consultancy; Abbvie: Consultancy; Jazz Pharmaceuticals: Consultancy; Celgene /BMS: Consultancy, Speakers Bureau; Incyte: Consultancy; Roche: Consultancy; Astellas: Consultancy, Speakers Bureau; Daichii Sankyo: Consultancy. Erba: AbbVie Inc; Agios Pharmaceuticals Inc; Bristol Myers Squibb; Celgene, a Bristol Myers Squibb company; Incyte Corporation; Jazz Pharmaceuticals Inc; Novartis: Speakers Bureau; AbbVie Inc: Other: Independent review committee; AbbVie Inc; Agios Pharmaceuticals Inc; ALX Oncology; Amgen Inc; Daiichi Sankyo Inc; FORMA Therapeutics; Forty Seven Inc; Gilead Sciences Inc; GlycoMimetics Inc; ImmunoGen Inc; Jazz Pharmaceuticals Inc; MacroGenics Inc; Novartis; PTC Therapeutics: Research Funding; AbbVie Inc; Agios Pharmaceuticals Inc; Astellas; Bristol Myers Squibb; Celgene, a Bristol Myers Squibb company; Daiichi Sankyo Inc; Genentech, a member of the Roche Group; GlycoMimetics Inc; Incyte Corporation; Jazz Pharmaceuticals Inc; Kura Oncology; Nov: Other: Advisory Committee. Konopleva: KisoJi: Research Funding; Novartis: Other: research funding pending, Patents & Royalties: intellectual property rights; Rafael Pharmaceuticals: Other: grant support, Research Funding; Sanofi: Other: grant support, Research Funding; Ablynx: Other: grant support, Research Funding; Agios: Other: grant support, Research Funding; Eli Lilly: Patents & Royalties: intellectual property rights, Research Funding; Stemline Therapeutics: Research Funding; AstraZeneca: Other: grant support, Research Funding; Ascentage: Other: grant support, Research Funding; Calithera: Other: grant support, Research Funding; Reata Pharmaceuticals: Current holder of stock options in a privately-held company, Patents & Royalties: intellectual property rights; Cellectis: Other: grant support; Forty Seven: Other: grant support, Research Funding; F. Hoffmann-La Roche: Consultancy, Honoraria, Other: grant support; Genentech: Consultancy, Honoraria, Other: grant support, Research Funding; AbbVie: Consultancy, Honoraria, Other: Grant Support, Research Funding. Kantarjian: Aptitude Health: Honoraria; Novartis: Honoraria, Research Funding; Jazz: Research Funding; Immunogen: Research Funding; Pfizer: Honoraria, Research Funding; KAHR Medical Ltd: Honoraria; NOVA Research: Honoraria; Ipsen Pharmaceuticals: Honoraria; Taiho Pharmaceutical Canada: Honoraria; Astellas Health: Honoraria; Precision Biosciences: Honoraria; Daiichi-Sankyo: Research Funding; BMS: Research Funding; Astra Zeneca: Honoraria; Ascentage: Research Funding; Amgen: Honoraria, Research Funding; AbbVie: Honoraria, Research Funding. Wang: Immunogen: Current Employment. Malcolm: Immunogen: Current Employment. Zweidler-McKay: ImmunoGen: Current Employment. DeAngelo: Abbvie: Research Funding; GlycoMimetics: Research Funding; Pfizer: Consultancy; Shire: Consultancy; Incyte Corporation: Consultancy; Blueprint Medicines Corporation: Consultancy; Amgen: Consultancy; Agios: Consultancy; Autolus: Consultancy; Takeda: Consultancy; Jazz: Consultancy; Forty-Seven: Consultancy; Novartis: Consultancy, Research Funding. Daver: Pfizer: Consultancy, Research Funding; Novartis: Consultancy; FATE Therapeutics: Research Funding; Gilead Sciences, Inc.: Consultancy, Research Funding; Sevier: Consultancy, Research Funding; Hanmi: Research Funding; Abbvie: Consultancy, Research Funding; Daiichi Sankyo: Consultancy, Research Funding; Trovagene: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Genentech: Consultancy, Research Funding; Astellas: Consultancy, Research Funding; Glycomimetics: Research Funding; Novimmune: Research Funding; ImmunoGen: Consultancy, Research Funding; Trillium: Consultancy, Research Funding; Bristol Myers Squibb: Consultancy, Research Funding; Jazz Pharmaceuticals: Consultancy, Other: Data Monitoring Committee member; Dava Oncology (Arog): Consultancy; Celgene: Consultancy; Syndax: Consultancy; Shattuck Labs: Consultancy; Agios: Consultancy; Kite Pharmaceuticals: Consultancy; SOBI: Consultancy; STAR Therapeutics: Consultancy; Karyopharm: Research Funding; Newave: Research Funding.

BACKGROUND: Many efforts have been made in the attempt to address the conundrum question of fitness definition ad prognosis prediction in elderly acute myeloid leukemia (AML) patients. Parametric definitions are expected to give an advantage in patient stratification; however, clinical examination remain de facto pivotal to formulate therapy decisions and frequently the comorbidities are empirically evaluated. METHODS: We conducted a multicenter study collecting baseline comorbidity, laboratory data, CTCAE 4.0.3 adverse events (AE), and outcome of elderly patients (>65 years old) with new onset AML who received hypomethylating agents as 1st line therapy. We tested the impact on prognosis of baseline clinical and biological risk factors. Furthermore, we evaluated a score - acute myeloid leukemia-composite model, AML-CM (Mukherjee et al, 2017) - developed in chemotherapy-eligible patients, that accounts for baseline comorbidities, laboratory parameters, age and cytogenetic-molecular risk. The study was approved by local Ethical Authority (316/2019/Oss/AOUBo). RESULTS: We collected data from 131 consecutive elderly patients who received 1 st line HMAs between January 2008 and January 2021. Patients had a median age of 76 years (IQR 72 -79). Seventy-seven out of 131 patients (58.8%) had de novo AML, 32/131 (32.8%) had secondary AML, and 11/131 (8.4%) had therapy-related AML. Out of 123 evaluable patients, 43 (34.9%) had complex karyotype, 1 (0.8%) inv(16), 59 (48.4) normal karyotype, 18 (14.7%) other alterations; 8/108 patients harbored FLT3 ITD mutation (7.4%, 23 not tested), 12/101 NPM1 mutation (11.9%, 30 not tested). Based on these data, 111 patients were evaluable for ELN2010 risk stratification; 9 over 111 patients (8.1%) were stratified in the low risk, 42/111 (37.8%) in intermediate-1 risk, 17/111(15.3%) in intermediate-2 risk, and 43/111 (38.7%) in high-risk class. As expected, most of the patients had at least one comorbidity. Particularly, baseline arrhythmia was present in 29/130 (22.1%, 1 no data), cardiovascular comorbidity in 20/130 (15.4%, 1 no data), diabetes in 20/131 (15.3%), cerebrovascular comorbidity in 11/131 (8.4%), kidney disease in 15/130 (11.5%, 1 no data), lung chronic disease 19/130 (14.6% 1 no data), hypoalbuminemia in 25/111 patients (22.5%, 20 no data). With a median follow up of 28.2 months, median overall survival (OS) of the entire cohort was 15.8 months (95% C.I. 11.2-19.4). We confirmed that patient who obtained a response (complete remission, partial response, hematological improvement) after 2 months of therapy had the best OS (figure A, median OS of 21 months for responders vs 7.4 months for non-responders, p To test the impact of comorbidities combined with cytogenetic and molecular risk, AML-CM was used. Our results indicate that AML-CM score was able to stratify prognosis in elderly patients receiving frontline HMAs (figure B, median OS in score group 1: 29.7 months, score group 2: 16.5 months, score group 3: 11.2 months, score group 4: 6.6 months, p=.038). The worse prognosis of patients with higher AML-CM score, which includes patients with increased baseline comorbidities, may be explained with a higher incidence of AEs (84.55, 116.01, 131.45, 229.3 events for 100 patients per year for score group 1,2,3, and 4, respectively) and infections (53.80, 55.10, 85.95, 140.13 events for 100 patients per year for score group 1,2,3, and 4, respectively), in patients with higher baseline comorbidities. CONCLUSION: In this study we found that baseline comorbidities, captured by AML-CM score, may define prognosis of elderly patients receiving 1st line HMAs; parametric comorbidity scores may improve our ability to predict outcome and tailor interventions. The impact of comorbidity on OS may be increased with novel and more aggressive therapy. For this reason, specific studies on functional fitness tests and geriatric assessments are highly warranted in patients receiving HMAs plus venetoclax. This work was supported by Bologna AIL. CP and AC shared last authorship. Figure 1 Figure 1. Disclosures Martinelli: Daichii Sankyo: Consultancy; Pfizer: Consultancy, Speakers Bureau; Astellas: Consultancy, Speakers Bureau; Roche: Consultancy; Abbvie: Consultancy; Stemline Therapeutics: Consultancy; Celgene /BMS: Consultancy, Speakers Bureau; Incyte: Consultancy; Jazz Pharmaceuticals: Consultancy. Cavo: Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel Accommodations, Speakers Bureau; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Honoraria; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Speakers Bureau; Adaptive Biotechnologies: Consultancy, Honoraria; GlaxoSmithKline: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Bristol-Myers Squib: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Papayannidis: Pfizer, Amgen, Novartis: Honoraria. Curti: Abbvie: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Jazz Pharma: Membership on an entity's Board of Directors or advisory committees.

Introduction In the setting of clinical trials Venetoclax (VEN) combined with hypomethylating agents (HMAs) has shown fair activity in Relapsed/Refractory (R/R) AML and impressive results in newly diagnosed (ND) elderly AML patients. However, no clear guidelines are available on real-life management, especially in the outpatient setting. This study involving AML patients treated with VEN combined with HMAs aims to amelioratate physicians' knowledge about the administration of these regimens. Methods This is a single-center retrospective study involving AML patients treated with Venetoclax combined with HMAs. Data were collected in accordance with GCP and Helsinky declaration. Adverse events (AEs) were graded according to CTCAE v4.03. Survival is estimated with Kaplan-Meyer method. Results A total of 59 AML patients, 43 R/R and 16 ND, have been treated with VEN plus HMAs from March 2018 to June 2021 and completed at least 1 therapy course (range 1-9, median 2, IQR 1.0 - 4.0). The median age was 70 (range 22-88) years and 15.3 % had a documented ECOG score greater than 1. VEN was combined with azacitidine in 35/59 (59.3 %) patients and with decitabine in 22/59 (37.3 %) patients (Table 1: patient and disease characteristics). The majority of patients (40/59, 67.8 %) (28/43 R/R, 12/16 ND) received the first cycle as out-patients, 19 out of 59 (32.2 %) patients were hospitalized and used as control. No significant differences with regards to disease and patients' characteristics were observed between in- and out-patients. During the ramp-up phase only 2 cases of tumor lysis syndrome (TLS) and 5 AEs were documented. During the first course, a total of 54 AEs were recorded and experienced by 16 over 19 hospitalized patients (84.2 %) and 20 over 40 outpatients (50 %). The 30-day and 60-day mortality were 2.5% (1/40) and 20 % (8/40), respectively, among patients receiving first course as out-patents, comparable to those documented in hospitalized patients. Overall, we reported 118 AEs, of which 74 were grade III-IV and the most common were hematological 23/74 (31.1 %) or infective 41/74 (55.4 %). Regarding infections, at least one bacterial infection was experienced in 10/40 (25%) and 12/19 (63.1%) patients of the outpatient and hospitalized cohorts, respectively (p = 0.009, IC 1.37 - 19.74, OR 4.98). Pneumonia and sepsis (13 and 18 cases) were the most frequent infections. Sepsis incidence was higher among hospitalized patients (13/19, 68.4 %, vs 5/40, 12.5 %, p = 0.000029). No significant difference in infective risk was documented between R/R and ND patients (65.1 vs 50 %). Thirty-two out of 59 (54.2 %) patients experienced at least one VEN withdrawal due to treatment toxicity. Twenty out of 43 AEs requiring VEN suspensions occurred during the first cycle. Patients treated in-patient showed the tendency for a higher probability to suspend therapy due to treatment toxicity (10/19 IN vs 10/40 OUT, p = 0.04). While twenty-three out of 59 (38.9 %) patients were hospitalized for treatment complications at least once, the average number of days spent in hospital was significantly different between patients receiving the first course as outpatients as compared to those who were hospitalized (5.9 vs 39.7, respectively, p < 0.0001). With a median follow-up of 117 days (IQR 92 - 173.75) in ND patients the Overall Response Rate (ORR), defined as CR + CRi + HI, was 62.5 % (10/16), with a CR/CRi rate of 50 % (8/16) and a median OS of 247 days (95% C.I. 177.71- 316.58)(Fig 1a). In the R/R setting the ORR rate was 41.8 % (18/43), with a CR/CRi rate of 25.6 % (11/43) and a median OS of 219 days (95% C.I. 91.8 - 346.2) (Fig 2a). No differences in OS were documented between patients who underwent VEN plus HMAs outpatient and patients who underwent the first cycle hospitalized (p = 0,38) (Fig. 1b-2b). Conclusions With the limitations of a single-center retrospective study, our real-life data indicate that VEN plus HMAs is feasible in an outpatient management, with minimal TLS rate and no limiting toxicities. Of note, infections rate was acceptable, bacterial infections and sepsis risk were lower in outpatients than in hospitalized patients. There was no significant impact of the outpatient management on treatment effectiveness, with data in line with published AML cohorts. Further studies evaluating the clinical, social and economic impact of outpatient VEN-based treatments are highly warranted. Figure 1 Figure 1. Disclosures Papayannidis: Pfizer, Amgen, Novartis: Honoraria. Cavo: Adaptive Biotechnologies: Consultancy, Honoraria; GlaxoSmithKline: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel Accommodations, Speakers Bureau; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sanofi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Speakers Bureau; Novartis: Honoraria; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Bristol-Myers Squib: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Curti: Jazz Pharma: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees.

Background: Inotuzumab-ozogamicin (IO) is one of the drugs of choice for relapse/refractory (R/R) acute lymphoblastic leukemia (ALL). Patients who received IO in a clinical trial had a CR rate of approximately 81% and a median overall survival of approximately 8 months, superior to best available therapy and numerically comparable with blinatumomab. Toxicities were generally manageable, veno-occlusive disease/ sinusoidal obstruction syndrome (VOD/SOS) was reported as a rare adverse event possibly linked to the drug that require attention, especially during hematopoietic stem cell transplant after IO. Data on IO effectiveness in the real-life setting are generally lacking, for the low incidence of the disease and the high number of possible therapies that are emerging. Methods: INO-CD22 (NCT03898128) is a real-life study collecting data on safety, effectiveness and indirect costs of IO therapy in R/R ALL. Twenty-four Italian institutions enrolled patients who received IO in the post-market expanded access program or with national health system reimbursement. This study was approved by the ethical committee (Prot.9296/2018). Here we present preliminary results of effectiveness and treatment emergent toxicity. Results: From 2014, we collected data of 65 patients who received IO and were evaluable for effectiveness and toxicity. Median age at start of IO was 47 years (IQR 27-61), 35 patients (53.9%) were male, 14 (21.5%) had Ph+ ALL. 12 patients (18.5%) received IO after 1 previous line of therapy, 16 (24.6%) after 2 previous lines, and 37 (56.9%) after more than 2 lines. In our patient set, 37 (56.9%) patients received IO after blinatumomab failure and 24 (36.9%) after an allogenic HSCT. Nine patients (13.8%) received IO after an history of mild to moderate liver-related adverse events. Median number of IO courses administered was 1 (IQR 1-2). Three patients do not complete course 1, as they died for infection (2) and cerebral hemorrhage (1). Of the 60 patients who were alive after a course of IO, 56 have evaluable data, 47 (83.9%) obtained a complete remission with IO. Particularly, CR was obtained in 9/11 (81.8%), 11/15 (73.3%), and 27/30 (90.0%) evaluable patients who received IO as a 1 st, 2 nd or >2 nd salvage, respectively. Twenty-four out of 30 (80.0%) evaluable patients who received IO after blinatumomab failure and 17/18 (94.5%) patients who already received an HSCT achieve CR with IO. With a median follow-up of 25.7 months (95% C.I. 19.8-34.3), median OS was 7.5 months (95% C.I. 5.8-10.0). Median OS was 7.5 months (95% C.I. 2.7-18.6), 9.0 months (95% C.I. 5.8-15.8), and 6.4 months (95% C.I. 4.5-12.8) in patients who received one previous line of treatment, two lines of treatment, and more than two lines of treatment, respectively (figure A). Median PFS was 4.1 months (95% C.I. 0.1-13.21), 6.7 months (95% C.I. 0.1-12.4), and 5.0 months (95% C.I. 3.12-7.9) in patients who received one previous treatment line, two previous lines, and more than two lines, respectively. Patients who received IO after blinatumomab failure had a median OS of 6.0 months (figure C, 95% C.I. 4.7-9.3). Patients who received IO after an HSCT had a median OS of 6.4 months (figure C, 95% C.I. 3.1-24.7). Twenty-five patient (38.5%) received an HSCT after IO therapy, of 22 (88.0 %) in CR, and 1 (6.7%) after further salvage therapies (chemotherapy). During IO therapy, 1 treatment related toxic death and 1 treatment related VOD/SOS, 1 grade 5 infection (AE), 9 grade 3-4 AEs, and 25 grade 1-2 AEs were noted. The most common AEs during IO therapy were Thrombocytopenia (reported in 7 (10.8%) of patients), infections (reported in 6 (9.2%) of patients) and liver tox adverse events (reported in 6 (9.2%) of patients). Overall, 7 VOD-SOS were reported, and the incidence was higher during transplant. Conclusions: Our data confirm in the real-life setting the great effectiveness of IO in term of CR. OS was comparable with data reported in clinical trials, even in a patient population that was not selected with inclusion criteria. OS and CR rate was not dramatically diminished in patients who already received HSCT nor in patients who already received blinatumomab. Safety of IO treatment was confirmed. IO is an easy-to-administer and safe therapy with a very high rate of expected CR in all the contexts and that confer promising expectation of survival. Figure 1 Figure 1. Disclosures Papayannidis: Novartis: Honoraria; Pfizer: Honoraria; Amgen: Honoraria; AbbVie: Honoraria; Astellas: Honoraria; Janssen: Honoraria. Fracchiolla: Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Jazz: Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Honoraria, Membership on an entity's Board of Directors or advisory committees. Di Raimondo: Amgen: Honoraria; AbbVie: Honoraria; Pfizer: Honoraria; Jazz Pharmaceutical: Honoraria; Janssen Pharmaceuticals: Honoraria; Bristol Myers Squibb: Honoraria. Lanza: Pfizer: Research Funding; Abbvie: Consultancy; Jazz: Consultancy; Sanofi: Consultancy. Borlenghi: Amgen, Janssen: Consultancy. Sica: Pfizer: Honoraria. Corradini: AbbVie, ADC Theraputics, Amgen, Celgene, Daiichi Sankyo, Gilead/Kite, GSK, Incyte, Janssen, KyowaKirin, Nerviano Medical Science, Novartis, Roche, Sanofi, Takeda: Honoraria; AbbVie, ADC Theraputics, Amgen, Celgene, Daiichi Sankyo, Gilead/Kite, GSK, Incyte, Janssen, KyowaKirin, Nerviano Medical Science, Novartis, Roche, Sanofi, Takeda: Consultancy; KiowaKirin; Incyte; Daiichi Sankyo; Janssen; F. Hoffman-La Roche; Kite; Servier: Consultancy; Amgen; Takeda; AbbVie: Consultancy, Honoraria, Other: Travel and accommodations; Novartis; Gilead; Celgene: Consultancy, Other: Travel and accommodations; BMS: Other: Travel and accommodation; Sanofi: Consultancy, Honoraria; Incyte: Consultancy; Novartis, Janssen, Celgene, BMS, Takeda, Gilead/Kite, Amgen, AbbVie: Other: travel and accomodations. Luppi: Abbvie: Honoraria; Novartis: Honoraria; Sanofi: Honoraria; MSD: Honoraria; Gilead Science: Honoraria, Other: Travel grant; Daiichi-Sankyo: Honoraria; Jazz Pharma: Honoraria. Pane: Novartis Pharma SAS;: Research Funding; AbbVie; Amgen; Novartis: Other: Travel, accommodation, expenses; AbbVie; Amgen; Novartis, GSK, Incyte: Speakers Bureau; AbbVie; Amgen; Novartis, GSK , Incyte: Consultancy. Passamonti: Janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; AbbVie: Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Martinelli: Stemline Therapeutics: Consultancy; Astellas: Consultancy, Speakers Bureau; Roche: Consultancy; Incyte: Consultancy; Celgene /BMS: Consultancy, Speakers Bureau; Abbvie: Consultancy; Pfizer: Consultancy, Speakers Bureau; Daichii Sankyo: Consultancy; Jazz Pharmaceuticals: Consultancy.

BACKGROUND. SEL24/MEN1703 is a first-in-class, orally available, dual PIM/FLT3 kinase inhibitor investigated in unselected AML patients in the First-in-Human, Dose Escalation (DE) and Cohort Expansion (CE) CLI24-001 trial (DIAMOND-01, ClinicalTrials.gov identifier: NCT03008187). The study has completed both the DE and CE part showing an acceptable safety profile up to the recommended dose (RD), with initial evidence of single agent efficacy particularly clustering in patients with IDH mutant disease. Previous studies conducted on a limited number of patients in the DE cohort indicated pS6, a downstream target in the PIM/FLT3 signaling pathway, as a biomarker of target engagement. AIM. To assess the relevance of pS6 as a pharmacodynamic (PD) biomarker in SEL24/MEN1703-treated patients. Moreover, patients were characterized on the basis of genetic profile to identify mutations which might cluster in patients' samples that demonstrated significant target engagement. Finally, longitudinal assessment of Variant Allelic Frequency (VAF) has been implemented. METHODS. S6 phosphorylation has been longitudinally monitored in the DIAMOND-01 study through an optimized assay for multiparametric analysis of phospho-protein activation. The assay allows a quantitative assessment of pS6 at the single cell level among blast cells as well as the identification of blast subpopulations in peripheral blood (PB). CD34+ Blast cells % was monitored to assess whether target engagement translated into blast reduction. Genotype analysis was performed by NGS using the Oncomine Myeloid Research Assay. RESULTS. PB samples from DE and CE patients, treated at 125 mg (RD) were analyzed, for a total of n= 27 assessable patients. At screening, we observed a heterogeneous positivity for pS6 marker in blast cells (range: 0.9%-79%), consistent with the unselected AML patient population recruited in the trial. Overall, 14/27 (51.8%) patients showed pS6 inhibition in blast cells at the end of Cycle 1 in comparison with screening (range: 70%-94%) (Figure 1). When SEL24/MEN1703 treatment continued beyond Cycle 1 (n=11 patients), pS6 inhibition was maintained and long-lasting in 6/11 (54.5%) patients. While pS6 inhibition did not translate into CD34+ blast decrease in all patients, long-lasting pS6 inhibition was observed in 2 out of 3 responding patients (including CRi as best response) evaluable for pS6 levels. Genetic characterization of these two patients treated at 125 mg (RD) showed that they harbored IDH mutations. CONCLUSIONS. The longitudinal PD assessment through the modulation of pS6 activation by flow cytometry confirmed that meaningful target engagement was achieved in more than 50% of patients treated with SEL24/MEN1703 at the RD. In most patients, including 2 out of 3 responders evaluable for pS6, its inhibition was maintained during the entire treatment. Preliminary genotyping showed that responding patients with strong pS6 inhibition harbored IDH mutations. In-depth analysis of genomic profiling and of the longitudinal assessment of VAF is ongoing in order to identify potential correlation with pS6 modulation and blast depletion in specific AML subsets, with the aim to define patient population(s) more likely to respond to SEL24/MEN1703. Figure 1. pS6 (%pS6*MFI) assessment in peripheral blast cells at screening and at C1D14-4H in CE patients treated at RD of 125 mg. Figure 1 Figure 1. Disclosures Paoli: Menarini Group: Current Employment. Bellarosa: Menarini Group: Current Employment. Bressan: Menarini Group: Current Employment. Bertolini: Gilead: Research Funding; Emercell: Research Funding. Montesinos: Teva: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Sanofi: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Stemline/Menarini: Consultancy; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Forma Therapeutics: Consultancy; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Karyopharm: Membership on an entity's Board of Directors or advisory committees, Research Funding; Daiichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Glycomimetics: Consultancy; Tolero Pharmaceutical: Consultancy; Agios: Consultancy; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Astellas Pharma, Inc.: Consultancy, Honoraria, Other: Advisory board, Research Funding, Speakers Bureau. Mukherjee: Eusa Pharma: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Teaching and Speaking; McGraw Hill: Honoraria, Other: Editor of Hematology Oncology Board Review (ongoing); Celgene Corporation: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Research/Independent Contractor, Research Funding; AAMDS in Joint Partnership with Cleveland Clinic Taussig Cancer Institute: Honoraria; Genentech: Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Research Funding; BioPharm: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Research/Independent Contractor, Research Funding; Bristol-Myers Squibb Co.: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Acceleron: Membership on an entity's Board of Directors or advisory committees; Blueprint Medicines: Membership on an entity's Board of Directors or advisory committees; Partnership for Health Analytic Research: Honoraria. Strickland: AbbVie, ArcherDx, Genentech, Incyte, Kura Oncology, Novartis, Pfizer, and Syros: Consultancy; Sunesis: Research Funding. Santoro: Takeda: Speakers Bureau; BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sanofi: Consultancy; Arqule: Consultancy, Speakers Bureau; Roche: Speakers Bureau; AbbVie: Speakers Bureau; Eli-Lilly: Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AstraZeneca: Speakers Bureau; Sandoz: Speakers Bureau; Eisai: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Gilead: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Servier: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Speakers Bureau; Amgen: Speakers Bureau; Novartis: Speakers Bureau; Bayer: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; MSD: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Walter: Jazz: Research Funding; Pfizer: Consultancy, Research Funding; Selvita: Research Funding; Amphivena: Consultancy, Other: ownership interests; Agios: Consultancy; Astellas: Consultancy; BMS: Consultancy; Genentech: Consultancy; Janssen: Consultancy; Kite: Consultancy; Macrogenics: Consultancy, Research Funding; Immunogen: Research Funding; Celgene: Consultancy, Research Funding; Aptevo: Consultancy, Research Funding; Amgen: Research Funding. Fazal: Taiho: Consultancy, Honoraria, Speakers Bureau; Stemline: Consultancy, Honoraria, Speakers Bureau; Sanofi Genzyme: Consultancy, Honoraria, Speakers Bureau; Novartis: Consultancy, Honoraria, Speakers Bureau; Karyopharm: Consultancy, Honoraria, Speakers Bureau; Jazz Pharma: Consultancy, Honoraria, Speakers Bureau; Janssen: Consultancy, Honoraria, Speakers Bureau; Incyte: Consultancy, Honoraria, Speakers Bureau; GlaxoSmithKline: Consultancy, Honoraria, Speakers Bureau; Gilead: Consultancy, Honoraria, Speakers Bureau; Celgene: Consultancy, Honoraria, Speakers Bureau; BMS: Consultancy, Honoraria, Speakers Bureau; Amgen: Consultancy, Honoraria, Speakers Bureau; Agios: Consultancy, Honoraria, Speakers Bureau; Takeda: Consultancy, Honoraria, Speakers Bureau; Tolero: Consultancy. Ravandi: Novartis: Honoraria; AstraZeneca: Honoraria; Xencor: Honoraria, Research Funding; Astex: Honoraria, Research Funding; Jazz: Honoraria, Research Funding; Taiho: Honoraria, Research Funding; Prelude: Research Funding; Agios: Honoraria, Research Funding; AbbVie: Honoraria, Research Funding; Amgen: Honoraria, Research Funding; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Syros Pharmaceuticals: Consultancy, Honoraria, Research Funding. Brzozka: Ardigen: Current Employment, Membership on an entity's Board of Directors or advisory committees; Ryvu Therapeutics: Current Employment, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Selvita SA: Current Employment, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees. Rzymski: Ryvu Therapeutics: Current Employment, Current equity holder in publicly-traded company. Mazan: Ryvu Therapeutics: Current Employment; Selvita SA: Current Employment. Baldini: Menarini Group: Current Employment. Ravenni: Menarini Group: Current Employment. Binaschi: Menarini Group: Current Employment. Laurent: Menarini Group: Current Employment. Pellacani: Menarini Group: Current Employment.

Introduction A large body of evidence has increasingly demonstrated that the immune tumor microenvironment (TME) critically contributes to acute myeloid leukemia (AML) development. However, current AML prognostic classifications only rely on leukemia cell-intrinsic alterations and do not incorporate immunological markers referring to TME. Indoleamine 2,3-dioxygenase 1 (IDO1), which is negatively regulated by the BIN1 proto-oncogene, is a central mediator of immune tolerance in the AML TME. This study aimed to identify IDO1-interacting genes in the AML TME and to develop a prognostic immune gene signature. Methods Biological and clinical data of 732 patients with de novo AML treated with curative intent were retrieved from public TCGA and HOVON datasets. Patients >= 65 years were excluded from survival analyses. Co-expression analysis was performed through cBioPortal on TCGA data aiming at discovering new IDO1-interacting genes. Cox regression analysis was used to identify most survival-predicting genes in order to generate a prognostic score. Differential expression (DE) analysis was performed using the nSolver software package (NanoString Technologies, Seattle, WA). Results BIN1 and IDO1 expression were negatively correlated in HOVON cases (P Conclusions Our data identify PLXNC1 as a novel IDO1-correlated gene. A three-gene immune signature that includes PLXCN1, IDO1 and BIN1 strongly predicted clinical outcome in large AML cohorts. Moreover, IDO1 and PLXNC1 expression-based DE analysis generated an immunological signature highly predictive of prognosis. In light of the emerging role of immunotherapies for AML, our findings support the incorporation of TME-associated immune biomarkers into current AML classification and prognostication algorithms. Figure Disclosures Cavo: Jannsen, BMS, Celgene, Sanofi, GlaxoSmithKline, Takeda, Amgen, Oncopeptides, AbbVie, Karyopharm, Adaptive: Consultancy, Honoraria. Rutella:NanoString Technologies, Inc.: Research Funding; MacroGenics, Inc.: Research Funding; Kura Oncology: Research Funding.

JN and CP equally contributed Introduction In the setting of clinical trials Venetoclax (VEN) combined with hypomethylating agents (HMAs) has shown fair activity in R/R AML and impressive results in treatment-naïve elderly AML patients. However, no clear guidelines are available on real-life management, especially in the outpatient setting. This study involving R/R AML patients treated with VEN combined with HMAs aims to amelioratate physicians' knowledge about the administration of these regimens. Methods This is a single-center retrospective study involving AML patients treated with Venetoclax combined with HMAs. Data were collected in accordance with GCP and Helsinky declaration. Adverse events (AEs) were graded according to CTCAE v4.03. Survival is estimated with Kaplan-Meyer method. Results Thirty-one R/R AML patients have been treated with VEN plus HMAs from March 2018 to March 2020 and completed at least 1 therapy course (range 1-9, median 2, IQR 1.0 - 5.0) (Table 1: patients' characteristics). Seventeen out of 31 (54,8 %) had received intensive chemotherapy as induction therapy. Twenty-two patients (71 %) had already received HMAs therapy, of which 14/31 (45,2 %) as first and only previous line of therapy. VEN was combined with azacitidine in 13/31 (41,9%) and with decitabine in 18/31 patients (58.1 %). The majority of patients (22/31, 70,9%) received the first cycle as out-patients, special focus of our analysis. For clinical reasons, only 9 out of 31 (29,1 %) patients were hospitalized and were used as control. In the outpatients setting, VEN dose escalation was managed with at least a weekly laboratory and clinical monitoring and the drug was often increased more slowly to carefully prevent tumor lysis syndrome or other complications. Specifically, there has been a trend toward a ramp-up schedule different from that indicated in clinical trials in the outpatient setting in comparison with hospitalized patients (77,2 % vs 33,3 %). In term of safety, no cases of tumor lysis syndrome (TLS) and only 2 AEs were documented during ramp-up phase, both experienced by hospitalized patients. Seventeen AEs were documented during cycle 1, affecting more frequently hospitalized patients (77,9% vs 31,8 %). In the outpatient setting, the early 30-days and 60-days mortalities were 4,5 % (1/22) and 13,6 % (3/22), respectively, comparable to percentages documented in hospitalized subgroup (0% and 11,1%). Overall, with a median follow-up of 138 days (IQR 69 - 285), we reported 48 AEs, of which 28 were grade III-IV and the most common were hematological (13/28, 48,1 %) or infective (14/28, 51,8 %). Twenty out of 31 (64,5 %) patients reduced VEN dosage during treatment, of which 12/20 (60 %) due to occurring AEs, and remaining patients for azole coadministration. Eleven out of 31 (35,5 %) patients required hospitalization, specifically 3 out of 9 hospitalized patients (33,3 %) during the subsequent outpatient phase of treatment, and 8/22 (36,3 %) patients who underwent VEN therapy outpatient, of which only 2 during the first 28 days of treatment. Twenty-four and 5 AEs were followed by a VEN temporary (median duration 14 days, range 5-120) and permanent withdrawn, respectively. As for the rate of response, the Overall Response Rate (ORR) by VEN plus HMAs therapy in our R/R study population, defined as CR + CRi + HI, was 41,9 % (13/31), with a CR/CRi rate of 22,6 % (7/31). The median time to first response was 67.0 days (IQR 37.0 - 133.5) and the median duration of response was 131.0 days (IQR 89.0 - 151.0). Four out of 31 (12,9 %) patients received subsequent HSCT. The median OS was 285 days (95% C.I. 178 - 392), with no difference in OS between patients who underwent VEN plus HMAs outpatient and patients who underwent the first cycle hospitalized (p = 0,38). Conclusions With the limitations of a single-center retrospective study, our real-life data indicate that VEN plus HMAs is feasible in an outpatient management, without TLS or other limiting toxicities and with comparable early-mortality and toxicity profiles, even in the ramp-up phase and first therapeutic cycle. There was no significant impact of the outpatient management on treatment effectiveness, with data in line with published R/R AML cohorts. Further studies evaluating the clinical, social and economic impact of outpatient VEN-based treatments are highly warranted. Disclosures Papayannidis: Abbvie, Janssen, Novartis, Amgen, Pfizer:Membership on an entity's Board of Directors or advisory committees, Patents & Royalties.Cavo:Jannsen, BMS, Celgene, Sanofi, GlaxoSmithKline, Takeda, Amgen, Oncopeptides, AbbVie, Karyopharm, Adaptive:Consultancy, Honoraria. OffLabel Disclosure: In R/R AML, available data regarding the combination of VEN plus HMAs come only from retrospective studies where VEN is administered as an off-label prescription due to its widespread approval for chronic lymphocytic leukemia due to promising results obtained in treatment-naive elderly AML patients

Background: Gilteritinib monotherapy provides a CR/CRh rate of 34% and a median event-free survival of 2.3 months in relapsed FLT3 mutant AML. Many AML patients (pts) who relapse after gilteritinib still express mutant FLT3 receptor and could potentially respond to FLT3 inhibition. Crenolanib is a type I, pan-FLT3 inhibitor which can be given as monotherapy or combined at full doses with standard salvage chemotherapy. Methods: We here report our experience with 7 consecutive pts who received crenolanib on compassionate basis after progressing on gilteritinib. IRB/local ethics approval was obtained prior to treatment for each pt and all pts signed informed consent forms. Results: Prior Treatment history: From Sep 2019 to July 2020, 7 consecutive pts with multiply relapsed FLT3-mutant AML who received compassionate use crenolanib after progressing on gilteritinib were identified. Four pts had relapsed after allogeneic HSCT (one pt had undergone two HSCT) and the other 3 were primary refractory despite multiple prior lines of therapy (range 2-5, median 4). Clinical presentation: At the time of treatment all pts had bone-marrow infiltration or greater than 20% circulating blasts. 1 pt did not undergo BM assessment prior to salvage chemotherapy and crenolanib but had 87% circulating blasts in the peripheral blood. One pt had cranial nerve palsy due to leukemic meningitis, another pt had extramedullary relapse in spleen and lymph nodes. Five pts had FLT3-ITD (1 of whom also had the gate-keeper FLT3-F691L mutations); 1 had FLT3-D835 and 1 had both FLT3-ITD and TKD. Crenolanib treatment: Crenolanib at 100mg TID was administered with intensive salvage therapy in 3 pts (FLAG-IDA in 2, HiDAC in 1). In the other 4 pts crenolanib was given with a palliative intent (with decitabine in 2, with azacytidine in 1 and as monotherapy in 1). Tolerability of crenolanib: Crenolanib has been clinically well tolerated, with mild nausea and vomiting reported in 3 pts which was controlled by antiemetics without causing any drug interruptions. Two pts had elevated transaminases (which resolved as concomitant medications were discontinued). There were no cardiac toxicities, pericardial effusion, fluid retention or weight gain. Response to crenolanib: At the time of this abstract, 5 of the 7 pts remain on crenolanib from a period of 18-160 days. Six of 7 pts reported clinical benefit with crenolanib. Of the 3 pts being treated with curative intent, the pt with extramedullary disease in the spleen and lymph nodes had complete resolution of her AML by PET scan. She also had exhibited clearance of bone-marrow blasts with full count recovery and became FLT3 negative. The pt with FLT3-F691 mutation and cranial nerve palsy due to CNS leukemia had clearance of CNS blasts and improvement in cranial nerve function after HIDAC, crenolanib, and intrathecal cytarabine; this patient achieved morphologic leukemia free state and FLT3 negativity in the BM. A 22-year-old pt treated with FLAG-IDA has only received 18 days of crenolanib at time of data cutoff. All pts treated with curative intent continue on crenolanib. Of the 4 pts treated with palliative intent, the pt with mutant TP53 had no benefit following crenolanib and azacytidine and died within two months. One patient, who had had two prior HSCTs, had 90% reduction in circulating blasts with azacytidine + crenolanib, but chose to discontinue treatment after 9 days. The other 2 pts continue on crenolanib 2 and 5 months after starting treatment. Conclusion: With the widespread availability of gilteritinib, more pts are now in need of treatment options after gilteritinib refractoriness or treatment failure. These pts often have resistant clones due to either acquisition of the gate-keeper FLT3-F691 mutation or RAS mutant clones. In this consecutive case series of 7 post-gilteritinib pts, treated in US and Europe, crenolanib can be given at full doses in combination with intensive salvage chemotherapy or decitabine/azacitidine. The individual-patient-level experience suggests crenolanib could effectively clear FLT3-ITD and variant FLT3-TKD mutations in pts progressing from multiple lines of treatment including gilteritinib. Clinical trials combining crenolanib with salvage chemotherapy in relapsed and refractory AML with FLT3 mutations are ongoing. More information about crenolanib compassionate use program is available by emailing compassionate@arogpharma.com. Disclosures Goldberg: Celgene: Consultancy; Daiichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees; Aptose: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; ADC Therapeutics: Research Funding; Aprea: Research Funding; AROG: Research Funding; Celularity: Research Funding; Dava Oncology: Honoraria; Pfizer: Research Funding. Geyer:Amgen: Research Funding. Pardee:Rafael Pharmaceuticals: Consultancy; AbbVie: Consultancy; Genentech, Inc.: Consultancy; BMS: Consultancy, Honoraria, Speakers Bureau; Karyopharm: Research Funding; Rafael: Research Funding; Celgene: Consultancy, Honoraria, Speakers Bureau; Amgen: Honoraria, Speakers Bureau; Pharmacyclics: Speakers Bureau. Grunwald:Cardinal Health: Consultancy; Amgen: Consultancy; Amgen: Consultancy; Agios: Consultancy; Merck: Consultancy; Merck: Consultancy; Abbvie: Consultancy; Agios: Consultancy; Daiichi Sankyo: Consultancy; Agios: Consultancy; Abbvie: Consultancy; Abbvie: Consultancy; Trovagene: Consultancy; Daiichi Sankyo: Consultancy; Incyte: Consultancy, Research Funding; Celgene: Consultancy; Incyte: Consultancy, Research Funding; Astellas: Consultancy; Astellas: Consultancy; Astellas: Consultancy; Genentech/Roche: Research Funding; Premier: Consultancy; Premier: Consultancy; Janssen: Research Funding; Genentech/Roche: Research Funding; Genentech/Roche: Research Funding; Forma Therapeutics: Research Funding; Merck: Research Funding; Janssen: Research Funding; Forma Therapeutics: Research Funding; Forma Therapeutics: Research Funding; Trovagene: Consultancy; Premier: Consultancy; Merck: Consultancy; Daiichi Sankyo: Consultancy; Trovagene: Consultancy; Incyte: Consultancy, Research Funding; Pfizer: Consultancy; Celgene: Consultancy; Celgene: Consultancy; Cardinal Health: Consultancy; Pfizer: Consultancy; Amgen: Consultancy; Pfizer: Consultancy; Cardinal Health: Consultancy. Wang:Arog Pharmaceuticals: Current Employment. Pathan:Arog Pharmaceuticals: Current Employment. Messahel:AROG Pharmaceuticals: Current Employment.

Rationale: Inotuzumab ozagomicin (IO) has been linked to an increased incidence of veno-occlusive disease (VOD) and liver alterations. Most VOD events occurred during hematopoietic stem cell (HSCT) transplantation after IO therapy. We have previously described that the measurement of liver stiffness can anticipate the diagnosis of VOD in the context of HSCT. The mechanisms underlying the increased risk of VOD and liver damage in patients receiving IO are not well understood; in the pathogenesis endothelial damage, ozagomicin release and on-target off-tumor effects may be involved. Here, we aimed to assess the effects of IO on the changes of liver, vascular and biochemistry parameters. Methods: Intensive monitoring of the liver was incorporated into the standard of care of patients who received IO for relapsed or refractory (R / R) acute lymphoblastic leukemia (ALL). Upper abdomen ultrasound with Doppler was performed at baseline and at the end of therapy; liver stiffness measurement (LSM) by Fibroscan® (Echosens, Paris, France) at every IO course or at every IO infusion. With the exception of ursodeoxycholic acid, the patients did not receive prophylaxis for VOD. Data was collected after anonymous aggregation, in accordance with GCP and Helsinki declaration. Results are reported as median with interquartile ranges (IQR). Results: At data cut-off, 1st Apr 2019, 16 patient received baseline assessment and at least a post-IO assessment in our monitoring program. In our patent set, median age was 44.5 (IQR 30.7 - 64.0); 12/16 (75 %) patients relapsed after the last treatment and 4/16 (25 %) patients were refractory to the last treatment; patients received a median of 3 (IQR 2 - 3.7) lines before IO; 6/16 (37.5 %) patients undergone HSCT before IO, of which a patient had 1st and 2nd HSCT before IO; 5/16 (31.25 %) undergone HSCT after IO therapy (no patients had second HSCT after IO). Patients received a median of 2 (IQR 2.0 - 3.7) IO administration according to the schedule of the phase 3 trial. The median duration of the therapy was 61.5 days (IQR 43.2 - 114.0) and median progression-free survival in our population was 278.0 days (95% C.I. 264.0 - 292.0). In our patient set, we performed 113 biochemistry determination, 30 liver ultrasounds with Doppler and 116 LSM examination. One patient received a liver biopsy. Among the biochemical exams (AST, ALT, GGT and alkaline phosphatase) only the AST values significantly increased after 1st course of IO (from the median value of 21 U/L to 53 U/L after course 3). Liver ultrasound with Doppler revealed portal hypertension signs in half of the patients during IO monitoring program. Among these patients 7/16 (44%), 3/16 (17%), 5/16 (33.3%) and 3/16 (17%) showed splenomegaly, recanalization of the paraumbilical vein, dilatation of portal vein and ascites, respectively. Median LSM significantly increased from a baseline value of 6 kPa to 7.8 kPa after last post-IO assessment (p-value 7.1 kPa). With a median follow up of 387.5 days (IQR 182.8-524.5) we observed one VOD event (7%); the VOD was graded severe and occurred after HSCT post-IO. Conclusions: Our clinical experience represents the first step to better understand the IO-related liver alterations, as we described the frequency and relevance of quantitative markers. Most of the patients in our set developed ultrasound and/or elastography alteration during IO therapy. Furthermore, these alterations do not seem to correlate with biochemistry. Even if most of the patients had sub-clinical vascular and parenchymal alterations of the liver portal-hypertension related, VOD incidence in our set is comparable with literature. Long-term follow-up results are expected to test whether alterations return or evolve over time. Stratifying the tailored risk liver complications with prospective non-invasive and marker-driven strategies in term of IO dosing and HSCT timing could be a great benefit for patients. * FR and GM contributed to this manuscript equally # AC and CP contributed to this manuscript equally Figure Disclosures Martinelli: Roche: Consultancy; BMS: Consultancy; Novartis: Consultancy; Pfizer: Consultancy; ARIAD: Consultancy. Cavo:janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau; bms: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; novartis: Honoraria; takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau. Papayannidis:Amgen: Honoraria; Novartis: Honoraria; Teva: Honoraria; Pfizer: Honoraria; Incyte: Honoraria; Shire: Honoraria.

Background The oral anti-apoptotic B-cell lymphoma 2 protein inhibitor venetoclax has shown strong activity in R/R AML in controlled clinical trials, and recently impressive results in treatment-naïve AML elderly patients with acute myeloid leukemia. However, limited data are available in the real-life setting. Methods This is a multi-center (n=4), retrospective study involving patients with treatment-naïve or Relapsed/Refractory (R/R) AML treated with Venetoclax in combination with HMAs. Data were collected after anonymous aggregation, in accordance with GCP and Helsinky declaration. Adverse events (AEs) were graded according CTCAE v4.03. Survival is estimated with Kaplan-Meyer method. Results Forty-four patients have been prescribed Venetoclax from March 2018 to June 2019 and completed at least 1 course of venetoclax (range 1-8, median 2, IQR 2.0 - 4.0), being evaluable in this analysis. Patients's characteristics are summarized in Table 1. Five/44 (11.4%) patients had a low risk AML, 21/44 (47.7%) had an intermediate risk AML and 14/44 (31.8%) patients had a high risk AML, according to ELN 2017 risk stratification (4 patients had no available ELN risk at baseline). Six out of 44 (13.6%) patients received Venetoclax in combination with HMAs as first line of therapy, whereas 14/44 (31%) as first line rescue for resistant AML, 15/44 (34.1%) at first relapse, 9/44 (20.5%) for second or further R/R AML. Among R/R patients who received Venetoclax, 17/38 (44.7%) and 21/38 (55.2 %) had received chemotherapy or HMAs as induction therapy, respectively. Overall, Venetoclax was combined with azacitidine in 19/44 patients (43.2%), with decitabine in 19/44 patients (43.2%), with Low-dose of Cytarabine in 5/44 (11.4%), and was performed in monotherapy in 1/44 (2.3%) patient. Three out of 44 patients (6.8%) received a maximum dosage of 100 mg daily, 2/44 (4.5%) received 200 mg, 37/44 (84.1%) received 400mg and 2/44 (4.5%) received 600 mg. Fifteen out of 44 (34.1%) patients reduced the dosage of venetoclax for concomitant Azole administration. The median follow-up is 75.5 (IQR 45.2 - 178.5) days for patients who received upfront venetoclax therapy, while 143 (IQR 49.2 - 235.7) days for R/R patients. In the first-line setting, no patients reduced venetoclax dosage for concomitant adverse events; two neutropenia grade IV and two thrombocytopenia grade III have been documented. In the R/R setting, 14/38 (36.6%) patients reduced venetoclax dosage for concomitant adverse events. Specifically, we reported 22 adverse events, of which 10 were grade III-IV (5 neutropenia grade IV, 2 pancytopenia grade IV, 1 neutropenia grade III and 2 febrile neutropenia grade III). The overall CR rate is 16.7 % in newly-onset AML patients and 28.9 % in R/R patients, respectively. Two out of 6 treatment-naive patients had an evaluable response at 2 months after the beginning of Venetoclax treatment, and 2/6 had an evaluable 4-months response: 1 stable disease (SD) and 1 disease progression (PD) at 2 months,1 SD e 1 complete remission (CR )at 4 months. Thirty-one out of 38 R/R patients had an evaluable response at 2 months and 21/38 had an evaluable 4-month response: 10 CR, 1 complete response with incomplete hematologic recovery (CRi), 14 SD and 6 PD at 2 months; 6 CR, 10 SD and 3 PD at 4 months have been documented. After a short follow-up period (75.5 days), no patients who received Venetoclax as upfront therapy underwent an allogeneic hematopoietic stem cell transplantation (HSCT). On the other hand, after a longer follow-up period (143 days), 5 out of 38 patients (13.2%) received a HSCT after Venetoclax therapy among R/R patients. Median Overall Survival was not reached in the newly-onset cohort. In R/R setting, median OS was 253 days (95% C.I. 157-349). Interpretation These data extend to the real-life setting some previous evidence obtained from trials. In particular, our data confirm that venetoclax plus HMAs or LDAC has an acceptable toxicity profile and is safe and manageable. However, especially in the R/R setting, hematological toxicity represents the most frequent adverse event, arising some concerns about the optimal drugs management. Although our data suggest a similar clinical activity of venetoclax combinations to that reported in clinical trials, further studies from the real-life setting are highly warranted to confirm venetoclax efficacy under normal clinical practice. GG and JN equally contributed CP and AC equally contributed Disclosures Boccadoro: Janssen: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding; AbbVie: Honoraria; Mundipharma: Research Funding; Sanofi: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Amgen: Honoraria, Research Funding. Cavo:celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau; janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau; bms: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; novartis: Honoraria; takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Papayannidis:Shire: Honoraria; Pfizer: Honoraria; Incyte: Honoraria; Novartis: Honoraria; Amgen: Honoraria; Teva: Honoraria. OffLabel Disclosure: Venetoclax is not approved to treat Acute Myeloid Leukemia in Italy

Background Although much efforts have been made to precisely define fitness of AML patients, in patients who are not candidate to chemotherapy, there is no prognostic model and the respective weight of AML biology and patient fitness are not well established. Here we test AML-CM score (Sorror, JAMA 2018), that is validated in fit population, in a set of old AML patients who received HMAs. Methods We retrospectively collected data of consecutive patients who received HMAs in our institution from 1st Jan 2008 with an age > 65 years at AML diagnosis. AML-CM score was applied to all the patients. Patients were divided in 4 groups (score 1-4: group 1, score 5-6: group 2; score 7-9: group 3, score > 9: group 4) and in 2 macro-groups (score 1-6: group A and score > 6 group B) for the analyses. Descriptive data are presented as median with interquartile ranges (IQR). Adverse events are graded according to CTCAE v4.03. Survival analysis was conducted with Kaplan-Meyer and are presented as 95% confidence intervals (C.I.) and differences in overall survival (OS) were tested with 2-side log rank test. Fisher exact test and Person's chi squared test were used whenever appropriate. Results At data cut-off, 1st Jan 2019, 60 consecutive patients received decitabine or azacytidine as 1st line therapy for AML. Median age of the population was 75.94 years (IQR 72.53-80.38). Most of the patients (37/62, 59.7%) had de novo AML, 19/62 (30.6%) had AML secondary to previous myeloid disorders and 6/62 (9.7%) had AML secondary to chemotherapy or radiotherapy. Most of the patients were smokers (19/33, 57.57%, 29 no data), and few were usual drinkers (4/16, 25.00%, 46 no data). In our set, out of 62 patients, 2 patients (3.2%) had inv(3), 1 (1.6%) a translocation involving 11q23, 1 (1.6%) del(5q), 4 (6.4%) mon(7) or del (7q), 1 (1.6%) del(17p), 15 (24.2%) complex karyotype, 27 (43.5%) normal karyotype, 4 (6.5%) other alterations and 5 were not evaluable; 3/17 (17.65%, 45 no data) harbored IDH2 mutation, 1/16 (6.25%) IDH2 mutation, 2/33 FLT3 mutation (6.06%, 29 no data), 1/24 (4.17%, 38 no data), 2/15 (13.33%, 47 no data) TP53 mutation. According to ELN 2017, 3/62 patients (4.83%) had low risk, 34/62 (54.84%) intermediate risk and 23/62 (37.10%) high risk AML. According to AML-CM score, 13/62 patients (20.97%) were in group A, 20/62 (32.36%) in group B, 21/62 (33.87%) in group C, 6/62 (9.68%) in group D, 2/62 (3.23%) were not allocated for incomplete AML-CM score. There was no difference in term of age, ELN risk, secondary AML prevalence, HMA administered, or response to HMA according to ELN criteria between group 1, 2, 3, 4 or between macro-group A and B. Cardiovascular comorbidity, diabetes mellitus, obesity, previous tumor, hypoalbuminemia, elevated LDH were prevalent in higher risk AML-CM groups (3-4) and in macro-group B. Median OS was 658 days (95% C.I. 316-1000) in group 1, 556 days (95% C.I. 463-649 in group 2, 243 days (95% C.I. 153-353) in group 3, 107 days (95% C.I. 47-167) in group 4 (p=.021, figure 1A). Furthermore, we observed a median OS of 589 days (95% C.I. 328-850) in macro-group A and 219 days (95% C.I. 96-342) in macro-group B (p=.003, figure 1B). Reduced survival was correlated with a non-statistical trend toward augmented incidence of infections and adverse events in higher risk AML-CM groups (3-4). Conclusions AML-CM is a useful indicator of prognosis in old patients that receive HMAs. Prognosis in our set is influenced by comorbidity (measured with AML-CM, a quantitative score) more than by disease biology. We identified a group of patients (macro-group A) that has median OS after HMAs outlying OS reported in literature. This brilliant result can be due to lower comorbidity. AML-CM could help in defining candidate patients for therapy intensification and care utilization or for team comorbidity management. GM and RDN equally contributed Figure 1 Disclosures Martinelli: Roche: Consultancy; Novartis: Consultancy; ARIAD: Consultancy; BMS: Consultancy; Pfizer: Consultancy. Baccarani:Novartis: Consultancy, Speakers Bureau; Incyte: Consultancy, Speakers Bureau; Takeda: Consultancy. Papayannidis:Pfizer: Honoraria; Teva: Honoraria; Shire: Honoraria; Novartis: Honoraria; Amgen: Honoraria; Incyte: Honoraria. Cavo:janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau; bms: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; novartis: Honoraria; takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.

Introduction: ELN intermediate-risk AML poses considerable challenges to clinicians both in terms of accurate prognostication and optimal treatment. Indoleamine 2,3-dioxygenase 1 (IDO1) plays a central role as a mediator of immune tolerance in AML through the increase of Treg cells. IDO1 activity is negatively regulated by the BIN1 proto-oncogene. Herein, we analyzed the correlation between BIN1 and IDO1 expression in AML, also focusing on IDO1-interacting genes, with the aim to identify a predictive gene signature for OS. Methods: Biological and clinical data of 732 patients with de novo AML were retrieved from public TCGA and HOVON datasets. Since details on chemotherapy regimens were not available in the HOVON dataset, we decided to exclude patients >= 65 years from survival analyses. IDO1-interacting genes were selected through a co-expression analysis performed on TCGA RNA-sequencing data accessed through cBioPortal. The best genes combination predicting overall survival was plotted in a gene expression score. Patients were split in three different groups using score quartiles as cut-off. Results: In the HOVON dataset, IDO1 and BIN1 mRNA expression were negatively correlated (r = -0.40, P Conclusions: Our study shows a negative correlation between IDO1 and BIN1 in AML, suggesting IDO1 inhibition by BIN1, and identifies for the first time PLXNC1, a receptor for semaphorines, as an IDO1-interacting gene potentially implicated in immune response regulation. This finding corroborates the role of IDO1 and its interacting genes in the promotion of a tolerogenic microenvironment in AML. Lastly, our gene expression score predicted OS in intermediate-risk AML patients not undergoing HSCT, a finding which has clinical implications for accurate patient stratification and for clinical decision making, i.e., bridging these patients to transplant. Figure Disclosures Papayannidis: Pfizer: Honoraria; Amgen: Honoraria; Incyte: Honoraria; Novartis: Honoraria; Shire: Honoraria; Teva: Honoraria. Cavo:celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau; janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau; bms: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; novartis: Honoraria; takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Rutella:MacroGenics, Inc.: Research Funding; NanoString Technologies, Inc.: Research Funding; Kura Oncology: Research Funding.

Background Acute myeloid leukemia (AML) has been considered for a long time exclusively driven by critical mutations in hematopoietic stem cells (HSCs). Recently, the contribution of bone marrow (BM) microenvironment has gained increasing attention, challenging the evidence that AML derives exclusively from leukemic cell-intrinsic defects. Mesenchymal stromal cells (MSCs) are a key component of the BM microenvironment by regulating HSC fate and having a unique immune-modulatory capacity mostly mediated by interferon (IFN)-γ-induced indoleamine 2,3-dioxygenase (IDO)-1 enzyme activity. New studies demonstrated that the alterations of MSCs are able (e.g. by promoting an inflammatory/genotoxic microenvironment) to induce hematological diseases in mice models and humans. Moreover, AML cells seem to exploit MSC-dependent pro-survival signals to their advantage. All these concepts converge to indicate a fundamental bi-directional interaction among malignant cells and BM microenvironment contributing to AML onset and progression. The mechanisms underlying this crosstalk have just been started to get unraveled. Among signals potentially driving the remodeling of the BM microenvironment, inflammation, a hallmark of cancer, seems to play a role. We hypothesize that 'inflammatory features' of leukemic cells can shape MSCs by inducing functional changes able to create a permissive/self-reinforcing niche favorable to escape therapy and immune response. Methods We isolated acute myeloid leukemia (AML) cells and generated AML-MSCs from the BM of AML patients. Gene expression profile (GEP) (AML, N=61; healthy donors, HDs N=7) and NanoString analysis (AML, N=24) on BM-derived cells were also done. Next, we set up AML-MSC/AML cell co-culture experiments and we investigated gene expression in AML-MSCs and AML cells before and after co-cultures. We also set up a murine model in which the IFN-γ expressing C1498 AML cells was knock down (KD) for the IFN-γ gene by RNA interference. BM infiltrate was analyzed in mice and AML patients. Results In a GEP-screening, we found that almost 40% of AML samples showed an IFN-γ expression higher than the median level of IFN-γ expression in HDs. NanoString data and pathway analysis indicated that IFN-γ high AML cells (above the median level) presented an inflammatory/immune modulating signature clearly distinct from IFN-γ low AML cells (below the median level). Moreover, IFN-γ expression in AML samples correlated with the up-regulation of IFN-γ-stimulated genes (ISGs) (e.g. IDO-1, Programmed death-ligand (PDL)-1 and Nitric Oxide synthase (NOS)-2), which are known to regulate immunity and tolerance. Thus, we aimed to gain insights into IFN-γ-dependent modifications in the leukemic milieu. In AML-MSC/AML cell co-culture experiments, we detected that AML cells produced IFN-γ. To gain insight in AML cell-dependent MSC modifications, we analyzed ISG expression in MSCs, after co-cultures with IFN-γ high or IFN-γ low AML cells. We found that IFN-γ high, but not IFN-γ low AML cells, were able to induce IDO-1, PDL-1 and NOS-2 in AML-MSCs. Moreover, ISG upregulation was abrogated by an IFN-γ neutralizing antibody. We also found that AML-MSCs, after co-culture with IFN-γ high AML cells, were able to induce regulatory T cells (Tregs) in an IDO1-dependent manner. In vivo experiments showed a higher percentage of engraftment in immunocompetent mice injected with parental IFN-γ expressing cells compared to mouse injected with the KD counterpart. The take of parental C1498 cells was associated to an increased frequency of Tregs in the BM. Furthermore, the BM microenvironment of mice injected with IFN-γ KD-C1498 cells showed a significant reduction of PD-L1 expressing cells. Consistently, BM infiltrate analysis in AML patients showed that the percentage of Tregs was correlated with the percentage of AML IFN-γ-positive cells in the BM. Conclusion Our data suggest that interferon-γ-dependent inflammatory signals produced by AML cells are able to modify MSC functions, thus favoring an immune modulating and leukemia-supporting milieu. Overall, our results unravel MSC-dependent mechanisms that might promote leukemia resistance to therapy, therefore informing the delivery of novel therapies targeting the AML microenvironment such as IDO inhibitors and immune checkpoint blockade. Disclosures Martinelli: Novartis: Consultancy, Other: trial grant; Daiichi Sankyo: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria, Other: trial grant; Incyte: Consultancy, Other: trial grant; Janssen: Consultancy, Other: trial grant; Roche: Consultancy, Other: trial grant; Amgen: Consultancy, Other: trial grant; Ariad: Consultancy, Other: trial grant; Celgene: Consultancy, Honoraria, Other: trial grant; Pfizer: Consultancy, Other: trial grant. Rutella:Kura Oncology: Research Funding; NanoString Technologies, Inc.: Research Funding; MacroGenics, Inc.: Research Funding. Cavo:bms: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau; amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau; novartis: Honoraria.

Background. The incorporation of tyrosine kinase inhibitors (TKIs) in treatment schemes of Ph+ ALL has remarkably improved survival. In adult patients with Ph+ ALL, ponatinib in combination with chemotherapy showed a 3-year event-free survival rate of 69%, a 3-year overall survival (OS) of 83%, and a higher rate of response when compared with dasatinib plus chemotherapy. However, in unfit or elderly ALL patients, TKIs combined with chemotherapy are associations with higher toxicity. Therefore, we examined the efficacy and safety of steroids plus ponatinib alone for the treatment of elderly or unfit patients with Ph+ ALL in a multi-center Phase II prospective clinical Italian trial, GIMEMA LAL1811 (EudraCT number 2012-002761-35). Methods. From March 2014 to December 2016, we enrolled 44 patients with untreated Ph+ ALL, ≥ 60 years or unfit (i.e. for intensive chemotherapy and stem cell transplantation). Two out of 44 patients were not elegible for the study. Patients received oral administration of 45 mg/day of ponatinib for 8 consecutive courses of 6 weeks (w). Steroids were administered from day -14 to day 29 during course 1. Intrathecal therapy with methotrexate, cytarabine and dexametasone was performed every 28 days for central nervous system (CNS) disease prophylaxis. In patients with CNS disease at diagnosis, intrathecal therapy was administered twice a week until complete remission. Dose reduction of ponatinib was allowed for adverse events. Patient samples were obtained at diagnosis and at every course, BCR-ABL mutational analisys and BCR-ABL/ABL ratio by quantitative real time PCR was performed. Complete molecular response (CMR) was defined as BCR-ABL/ABL ratio below 0.01 or undetectable, and with a sensitivity of at least 30,000 molecules of ABL. Results. Forty-two patients were eligible for the study. Median age was 68 years (range 27-85). Nine out of 42 patients were At week 24, 15/42 patients still received 45 mg of ponatinib daily, only 4/42 patients permanently withdrew study drug. During the study, 75 adverse events (AE) were reported; 36 of the 75 AEs were considered related to ponatinib. Twenty-six of the 75 AEs were considered serious (SAE); 13/26 SAEs were considered related to ponatinib. A death was suspected to be related to ponatinib. We performed BCR-ABL mutational analysis in 22 patients at diagnosis, and 15 patients at 24w. T315L (abundance 100%) was detected in a patient relapsed during ponatinib therapy. We could not identify the emergency of other mutations. Conclusions. Ponatinib and steroid show a high efficacy in newly diagnosed unfit/elderly Ph+ ALL patients. Toxicities were manageable and cardiovascular AEs were limited. In the small cohort of patients relapsed in the study, relapse mechanisms were unclear; only one patient had evidence of mutations that caused resistance to ponatinib. The fast and deep reduction of the disease burden in the majority of patients, the ability of ponatinib to prevent the emergence of clones harboring BCR-ABL mutations, and the synthetic lethality with steroids on the BCR-ABL, FLT3, HCK, CDK6, MCL1 pathway could explain the therapeutic effectiveness. Acknowledgments. GIMEMA, ELN, AIL, AIRC, Regione-Università 2010-12, FP7 NGS-PTL, HARMONY, Fondazione del Monte BO e RA. Disclosures Soverini: Bristol-Myers Squibb: Consultancy; Incyte Biosciences: Consultancy; Novartis: Consultancy. Bocchia: Novartis: Other: Travel grant; Celgene: Other: Travel grant; Roche: Other: Travel grant; Jansen: Other: Travel grant. Cuneo: Abbvie: Honoraria, Other: Advisory Board; Janssen: Honoraria, Other: Advisory Board; Gilead: Honoraria, Other: Advisory Board; Roche: Honoraria, Other: Advisory Board. Bonifacio: Pfizer: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte: Membership on an entity's Board of Directors or advisory committees. Falini: Roche: Research Funding. Galieni: Takeda: Other: Advisory Board; Abbvie: Other: Advisory Board. Foà: Sandoz: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; AbbVie: Consultancy, Speakers Bureau; Roche: Consultancy, Speakers Bureau; janssen: Consultancy, Speakers Bureau; Gilead: Consultancy, Speakers Bureau; Amgen: Consultancy, Speakers Bureau; Celgene: Consultancy, Speakers Bureau; BMS: Consultancy, Speakers Bureau. Baccarani: Pfizer: Honoraria, Speakers Bureau; Bristol-Myers Squibb: Honoraria, Speakers Bureau; Incyte ARIAD: Consultancy, Honoraria, Speakers Bureau; Novartis: Consultancy, Honoraria, Speakers Bureau.

In Philadelphia-positive (Ph+) Acute Lymphoblastic Leukemia (ALL) patients (pts), resistance to tyrosine kinase inhibitors (TKIs) is frequently associated with the selection of one or more mutations in the BCR-ABL1 kinase domain (KD). The swift emergence of mutant clones as early as during induction therapy supports the hypothesis that, at least in some cases, mutations may already be present at diagnosis. Next Generaton Sequencing (NGS) has been proposed as an alternative to Sanger sequencing (seq) for BCR-ABL1 KD mutation screening because of its greater sensitivity and accuracy, but no studies have so far evaluated its prospective use in Ph+ ALL. Between 2015 and 2018, we have used NGS in parallel to Sanger seq to analyze a consecutive series of 126 Ph+ ALL pts who were newly diagnosed (n=39) or who had relapsed/refractory disease (n=87) on TKI therapy. In 22 cases, both bone marrow and peripheral blood were analyzed and compared. NGS of ≈400bp amplicons generated by nested RT-PCR was performed on a Roche GS Junior (until April 2017) or on an Illumina MiSeq (from May 2017 on). Read alignment and variant calling (with a lower limit set to 3%) were done with the AmpSuite software (SmartSeq srl). When multiple mutations mapped within the same sequence reads, assessment of cis vs trans configuration was done correcting for the probability of PCR recombination. Three out of 39 (7.7%) de novo Ph+ ALL pts had low burden point mutations detectable by NGS: one had a V289A (variant frequency, 3.4%); one had a D276G (4.0%) and a F359V (3.5%); one had an E255K mutation (3.3%). The first pt was enrolled in the GIMEMA LAL1811 study of frontline ponatinib; the second and the third pts were enrolled in the GIMEMA D-ALBA study of frontline sequential treatment with dasatinib and blinatumomab. All pts achieved molecular remission, consistently with the mutations being sensitive to the TKIs received. The 35INS insertion/truncation mutant was detected in 27 (69%) pts, who all have so far achieved molecular remission. This is in line with the report by O'Hare et al (Blood 2011) suggesting that the 35INS variant is kinase-inactive and does not contribute to TKI resistance. For this reason, the 35INS was excluded from subsequent analyses. Relapsed/refractory pts positive for mutations by Sanger seq were 57 (65%); those positive for mutations by NGS were 69 (79%). Fifty-six out of 87 (49%) pts had >1 mutation (up to 13) detected by NGS. NGS identified low burden mutations (i.e., mutations present in a proportion of transcripts between 3 and 20%) in 12 pts who were negative for mutations by Sanger seq. Most importantly, NGS provided a more accurate picture of BCR-ABL1 mutations status in 40 (46%) pts who turned out to have one or more low burden mutations in addition to the dominant mutation(s) detectable by Sanger seq. In all cases, each low burden mutation detected by NGS could be recognized as poorly sensitive either to the TKI the pt was receiving at the time of testing, or to the previous TKI. The clonal nature of NGS-based analysis further proved its utility i) in 4 pts where Sanger seq had shown 2 base substitutions in the same codon so that the actual amino-acid change(s) were impossible to infer (a ponatinib-resistant pt with a T315M mutation, 2 dasatinib-resistant pts with various combinations of F317I, F317C and/or F1317L, a dasatinib-resistant pt with 2 different nucleotide substitutions both leading to the V299L), and ii) in 48/56 pts who had ≥2 mutations whose clonal configuration could not be resolved. Twenty-eight out of these 48 pts were found to carry one or more (up to 3) compound mutants. Compound mutants were more common in pts who had failed ≥2 lines of therapy, whereas polyclonality was more common in pts who had failed first line therapy. The most frequent compound mutants were T315I+E255K and T315I+E255V. Interestingly, the latter was associated with poor or no response to ponatinib. Our results in a relatively large series of Ph+ ALL pts suggest that an NGS-based approach provides a more accurate characterization of the complexity of BCR-ABL1 KD mutation status, including compound mutants some of whom may be poorly sensitive even to ponatinib. Mutations may already be detected at the time of diagnosis. It remains to be assessed whether more sensitive techniques like digital PCR may identify a greater number of pts with pre-therapy mutations and whether the detection of pre-therapy mutations may be used to guide 1st-line treatment selection. Disclosures Soverini: Incyte Biosciences: Consultancy; Bristol Myers Squibb: Consultancy; Novartis: Consultancy. Pagano:Gilead: Speakers Bureau; Basilea: Speakers Bureau; Merck: Speakers Bureau; Janssen: Speakers Bureau; Pfizer: Speakers Bureau. Abruzzese:Ariad: Consultancy; BMS: Consultancy; Novartis: Consultancy; Pfizer: Consultancy. Martinelli:Roche: Consultancy; Celgene: Consultancy, Speakers Bureau; Jazz Pharmaceuticals: Consultancy; Pfizer: Consultancy, Speakers Bureau; Novartis: Speakers Bureau; Abbvie: Consultancy; Janssen: Consultancy; Ariad/Incyte: Consultancy; Amgen: Consultancy. Cavo:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Introduction. Mesenchymal stromal cells (MSCs) substantially contribute to the creation of hematopoietic niche by regulating hematopoietic stem cell (HSC) fate and have a unique immune-modulating capacity. In the leukemic milieu, the presence of MSCs constitutes a side effect, since MSCs not only favor leukemic cell survival, but they can also generate an immune-tolerant environment. Although recent findings have outlined a putative MSC role in hematological malignancy development, MSC-dependent mechanisms potentially supporting leukemia remain unclear. We hypothesize that leukemic cells can shape bone marrow (BM) MSCs by inducing functional changes, able to convert the BM microenvironment from hostile to permissive for leukemia. Methods. We isolated acute myeloid leukemia (AML) cells and generated AML-MSCs from the BM of AML patients. Next, we set up AML-MSC/AML cell co-culture experiments and we investigated gene expression in AML-MSCs and AML cells before and after co-cultures. Results. Our microarray data on BM isolated cells (AML patients, N=61; healthy donors, N=7) indicated Interferon(IFN)-γ as un up-regulated gene in almost 40% of AML samples. Furthermore, multivariate analysis, showed that IFN-g-positive AML patients had a better overall survival. Thus, we decided to deepen IFN-ϒ-dependent modifications in leukemic milieu through in vitro studies. In AML-MSC/AML cell co-culture experiments, we confirmed microarray data and we found that AML cells produced IFN-γ. We next demonstrated that indoleamine 2,3-dioxygenase (IDO)1 enzyme, a master regulator of MSC immune suppressive functions, is up-regulated in AML-MSCs after co-culture with IFN-γ-producing AML cells. Such effect was abrogated by adding to cell cultures an IFN-γ neutralizing antibody. Finally, we found that AML-MSCs, after co-culture with IFN-γ-producing AML cells, were able to induce regulatory T cell in a IDO1-dependent manner. To gain further insight in AML cell-dependent MSC modifications, we analyzed MSC expression of IFN-γ-stimulated genes (ISGs) such as Programmed death-ligand (PDL)-1 and Nitric Oxide synthase (NOS)-2 which are known to regulate immunity and promote tolerance. In particular, we tested the ISG expression in MSCs after co-cultures with IFN-ϒ positive or IFN-γ negative AML cells. We found that IFN-γ positive, but not IFN-γ negative AML cells, were able to induce PDL-1 and NOS2 in AML-MSCs. Thus, ISG expression profile in AML-MSCs after co-cultures with IFN-γ positive AML cells was similar as that observed in MSCs after exposure to recombinant IFN-γ. Conclusions. Our data suggest that inflammatory signals produced by AML cells are able to modify MSC functions, thus favoring an immune-tolerant and leukemia supporting milieu. Overall, our results would likely contribute to unravel MSC-dependent mechanisms promoting leukemia and will help to provide novel applications for drugs already under experimentation (e.g. IDO-inhibitors, Checkpoint inhibitors) to translate into more effective therapies in AML patients. Disclosures Cavo: AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Next-Generation Sequencing (NGS)-based BCR-ABL1 kinase domain (KD) mutation screening has been shown to enable greater accuracy and sensitivity and straightforward identification of compound mutants (CM) as compared to Sanger sequencing (seq). However, the prevalence of CMs has never been assessed in prospective studies, and although in vitro data suggest that many of them may be challenging for all tyrosine kinase inhibitors (TKIs) including ponatinib, attempts to correlate such data with in vivo responses have never been made. To address these issues, we have reviewed the results of routine NGS-based BCR-ABL1 KD mutation screening performed over the past 3 years. Between 2015 and 2018, we have prospectively used NGS to analyze a consecutive series of 751 Ph+ leukemia patients (pts) on TKI therapy who were eligible for BCR-ABL1 KD mutation screening according to ELN/NCCN/ESMO recommendations. The study population included 664 chronic myeloid leukemia (CML) pts with failure or warning response (chronic phase [CP], n=593; accelerated or blastic phase [AP/BP], n=71) and 87 Ph+ acute lymphoblastic leukemia (ALL) pts with relapsed/refractory disease. NGS of ≈400bp amplicons generated by nested RT-PCR was performed on a Roche GS Junior (until April 2017) or on an Illumina MiSeq (from May 2017 on) using custom protocols whose accuracy, sensitivity and reproducibility was checked by national and international (EUTOS) control rounds. Read alignment and variant calling was done using the AmpSuite software (SmartSeq srl), with a lower detection limit set to 3%. Cis or trans configuration of mutation pairs, indicating CMs or polyclonality, respectively, was determined correcting for the likelihood of PCR recombination. The 35INS insertion/truncation mutant was excluded from the analysis. NGS identified mutations in the BCR-ABL1 KD in a total of 313/664 (47%) CML pts (255/593 [43%] CP-CML and 58/71 [82%] AP/BP-CML) and 69/87 (79%) Ph+ ALL pts. Ninety-one percent of the mutations could be recognized as conferring resistance to at least one TKI on the basis of publicly available IC50 data or published reports. In 42/593 (7%) CP-CML, 6/71 (8.5%) AP/BP-CML and 12/87 (14%) Ph+ ALL pts, low burden mutations (i.e., mutations carried by a proportion of transcripts 15% - hence detectable by Sanger seq). Fifty-five (9.2%) CP-CML, 51 (72%) AP/BP-CML and 56 (49%) Ph+ ALL pts had ≥2 mutations (CP-CML: 1-5 mutations; AP/BP-CML: 1-6 mutations; Ph+ ALL: 1-13 mutations). Identification of CMs in pts with ≥2 mutations was fully possible (i.e., all the candidate pairs mapped within a distance of 400bp) in 71% of cases and partially possible (i.e., some, but not all the candidate pairs mapped within a distance of 400bp) in another 12% of cases. A total of 86 CMs (85 double and 1 triple) in 73 pts (21 [3.5%] CP-CML, 23 [32%] AP/BP-CML and 29 [37%] Ph+ ALL pts) could be catalogued (Figure 1A). All but two (T315I+D276G, M244V+E255K) were detected in pts who had received ≥2 TKIs and all included at least a 2nd-generation TKI-resistant mutation. The most frequent CMs were T315I+E255K, T315I+E255V, T315I+F359V, F317L+Y253H (Figure 1A). The triple CM, detected in a ponatinib-resistant pt, was F317I+Y253F+Q252H. Correlation of IC50 data with in vivo responses (the TKIs pts were clinically resistant to) confirmed only partially in vitro predictions (Figure 1B). In particular, although ponatinib was shown in vitro to be poorly effective against several CMs, only the T315I+E255V was consistently found to be associated with ponatinib failure. In conclusion, our results in a large unselected series of TKI-resistant pts analyzed by NGS show that:CMs are relatively infrequent in CP-CML, but may be a relevant issue in AP/BP-CML and Ph+ ALL;among pts with multiple mutations, those who have failed 1 line of therapy have most often polyclonality, whereas those who have failed ≥2 lines of therapy may have CMs or polyclonality;in vitro predictions of sensitivity and insensitivity based on IC50 data should be regarded with caution. In particular, the only compound mutant that we consistently found to be associated with ponatinib failure was the T315I+E255V. Supported by EUTOS 2016. Disclosures Soverini: Novartis: Consultancy; Incyte Biosciences: Consultancy; Bristol Myers Squibb: Consultancy. Pagano:Pfizer: Speakers Bureau; Gilead: Speakers Bureau; Basilea: Speakers Bureau; Merck: Speakers Bureau; Janssen: Speakers Bureau. Gugliotta:Pfizer: Honoraria; Bristol-Myers Squibb: Honoraria; Incyte: Honoraria; Novartis: Honoraria. Castagnetti:Incyte: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria; Bristol Meyers Squibb: Consultancy, Honoraria; Novartis: Consultancy, Honoraria. Angelucci:Roche Italy: Other: Local (national) advisory board; Novartis: Honoraria, Other: Chair Steering Comiittee TELESTO Protocol; Celgene: Honoraria, Other: Chair DMC; Jazz Pharmaceuticals Italy: Other: Local ( national) advisory board; Vertex Pharmaceuticals Incorporated (MA) and CRISPR CAS9 Therapeutics AG (CH): Other: Chair DMC. Martinelli:Abbvie: Consultancy; Ariad/Incyte: Consultancy; Janssen: Consultancy; Novartis: Speakers Bureau; Jazz Pharmaceuticals: Consultancy; Roche: Consultancy; Pfizer: Consultancy, Speakers Bureau; Celgene: Consultancy, Speakers Bureau; Amgen: Consultancy. Cavo:Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; GlaxoSmithKline: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Introduction. Inhibition of Bromodomain and extraterminal (BET) proteins was effective against different acute myeloid leukemia (AML) subtypes in preclinical studies (Dawson et al. Nature 2011; Zuber et al. Nature 2011; Dawson et al. Leukemia 2013; Chen et al. Cancer Cell 2014; Gröschel et al. Cell 2014; Zhao et al. Cell Reports 2016). However, the drug had limited clinical activity, suggesting the need of ad hoc combination therapies able to target leukemia stem cells (LSCs) in their microenvironment. Hypoxia is an integral component of the bone marrow microenvironment and plays a crucial role in survival and chemoresistance of LSCs. Aims. The study aims to elucidate the consequences of BETi treatment in AML under hypoxic conditions and identify novel potential combination strategies. Methods. AML cell lines (OCI-AML3: NPM1- and DNMT3A-mutated, Kasumi-1: t(8;21), HL60: MYC-amplified, MOLM-13, NOMO-1: MLL-driven, KG-1: TP53-mutated) were treated with the BET inhibitor (i) GSK1215101A (250/500 nM, 48h) or the NRF2 activator omaveloxolone (NRF2a, 0.2-1 mM, 48h) and with the drug combination (72h) at 1% or 20% O2 concentration. Cell viability, apoptosis and cell cycle were evaluated by trypan blue dye exclusion assay, AnnexinV and PI staining, respectively. Gene expression profiling (HTA2.0, Affymetrix) was carried out on actively translated mRNAs isolated by polysome profiling after 16h of BETi treatment and on 61 primary AML. The TCGA AML dataset was analyzed on the cBioPortal. Gene expression correlation and enrichment analysis were performed by Pearson coefficient and GSEA, respectively. Kaplan-Meier survival curves were compared by Logrank test. Glutathione was quantified by mass spectrometry (Metabolon). Results. BETi induced a dose-dependent reduction of cell viability in AML cells lines under hypoxia (25%-65% decrease at 500 nM) except for HL-60. Under the same conditions, the treatment caused a significant arrest in the G0/G1 phase of the cell cycle in OCI-AML3, Kasumi-1, HL-60 and KG-1 models (p Conclusions. BET protein activity drives alternative NRF2 or MYC overexpression in AML, which defines a subgroup of patients with poor prognosis. NRF2 activation is finely tuned in AML, as both inhibition and activation of the pathway induce cell death. However, NRF2 activation specifically potentiates BETi treatment under hypoxia and normoxia, suggesting a novel combination therapy against AML LSCs. Supported by: EHA Non-Clinical Junior Research Fellowship, ELN, AIL, AIRC, project Regione-Università 2010-12 (L. Bolondi), FP7 NGS-PTL project, Fondazione del Monte BO e RA project. Figure. Figure. Disclosures Cavo: Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Martinelli:Celgene: Consultancy, Speakers Bureau; Amgen: Consultancy; Pfizer: Consultancy, Speakers Bureau; Abbvie: Consultancy; Roche: Consultancy; Ariad/Incyte: Consultancy; Jazz Pharmaceuticals: Consultancy; Janssen: Consultancy; Novartis: Speakers Bureau.

Introduction Indoleamine 2,3-dioxygenase (IDO) is an intracellular heme-containing enzyme that catalyzes the initial rate-limiting step in tryptophan degradation along the kynurenine pathway. IDO is physiologically expressed by a wide variety of human cells in response to several stimuli and it is known to have a crucial role in the induction of immune tolerance during pregnancy, infections, transplantation, autoimmunity and tumors. IDO-mediated tryptophan degradation results in inhibition of T-cell proliferation, increase of T-cell apoptosis and T-reg induction. Several studies demonstrated that IDO production can induce the increase of Regulatory T-cells (Tregs) directly through the conversion of CD25- into CD25+ T cells, even in acute myeloid leukemia (AML) patients. IDO expression can be considered a novel mechanism of leukemia escape from immune control and its inhibition may represent an antileukemia therapeutic strategy. Aim of our work is to analyze IDO mRNA expression in a cohort of AML patients and to investigate the presence of any significant correlation between IDO expression and standard prognostic factors or clinical outcome. Methods We analyzed a cohort of 68 adult patients aged 18 years or older, who were diagnosed with de novo or secondary AML. IDO mRNA expression was evaluated by Real-Time (RT)-PCR in blood bone marrow and peripheral blood samples at diagnosis. Patients were then retrospectively stratified according to standard risk factors at diagnosis and to IDO mRNA expression levels. Results Median age of analyzed patients was 57 years (range 21-76). Fifty-nine out of 68 patients (87%) had de novo AML, whereas 9 out of 68 patients (13%) had secondary AML. A comprehensive risk assessment was available for 61 patients. Among these 61 patients who were evaluable for risk stratification, 13 patients (21%) resulted to have a favorable risk AML, 30 (49%) had an intermediate risk AML and 17 patients (30%) were stratified as high-risk AML. Sixty out of 68 patients received intensive, standard, induction chemotherapy regimens. The remaining 8 patients were not candidate to receive intensive chemotherapy mainly because of comorbidities. Twenty-three out of 68 patients (34%) were considered eligible for allogeneic stem cells transplantation (alloSCT) as consolidation therapy, after obtaining complete remission with standard chemotherapy. IDO expression in peripheral blood (PB) samples was between 0.07 and 4272.26 (median 5.60). Conversely, IDO expression in bone marrow (BM) samples was between 0.17 and 243.16 (median 1.21). Our data did not establish any significant correlation between IDO expression and leukemia risk factors at diagnosis, in particular cytogenetics, de novo or secondary AML, leukocytosis. Among the 60 patients who received induction chemotherapy, 35 achieved morphological complete remission (CR), 24 did not respond and 1 patient was not evaluable for response. Response to induction chemotherapy was not influenced by IDO mRNA expression levels. Interestingly, among patients undergoing alloSCT, high levels of IDO mRNA expression in PB samples negatively correlated with patients' overall survival. In particular, high IDO expression of more than 10 was associated with worse overall survival after alloSCT even when adjusted by patients' age and disease status at transplant (log rank P=0.02) (Fig.1). With the limitations of the low number of patients, these results from the group of transplanted patients were not likely due to differences in the incidence and severity of graft-versus-host-disease, whereas high IDO mRNA expression level was predictive of increased incidence of relapse. Conclusions This work suggests that IDO mRNA expression levels can be considered as predictive of AML outcome, independently from other risk factors at diagnosis. In our set, higher level of IDO mRNA expression at diagnosis was correlated with worse clinical outcome in patients undergoing alloSCT. Larger studies are warranted in order to establish the real predictive role of IDO mRNA expression in influencing AML outcome. Disclosures Cavo: Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau.

Background - Partner and localizer of BRCA2 (PALB2) plays a key role in the DNA damage repair (DDR). Genomic alterations of DDR genes rarely occur in AML, while their deregulation at transcriptional level is a known mechanism exploited by leukemic cells in order to sustain the high genetic instability and to continue proliferation. Aim - We aimed to characterize the role of PALB2 in AML by investigating its expression levels and its prognostic value, in order to evaluate its potential as target of therapies based on a synthetic lethality approaches. Methods - Gene expression profiling (GEP, Affymetrix) was performed on bone marrow cells of 7 healthy donors (HD) and 60 AML patients with more than 80% blast cells. K-means clustering of patients according to the expression of PALB2 was performed and differences in survival were assessed d by Kaplan-Meier survival analysis. Results - Our cohort was characterized by a median age at diagnosis of 60 years-old. Twelve out of 43 patients harbored a mutation in FLT3 (27.9%, 17 patients not tested); 8 patients were NPM1 mutated (27.6%, 31 patients not tested); 2 patients were TP53 mutated (3%, all patients tested). According to ELN2017 guidelines, 17 cases were high-risk AML, 38 cases were intermediate, 3 cases had low-risk classification and 2 cases were not classified due to the lack of prognostic markers. We detected variable levels of PALB2 mRNA (range 52.90-244.37) in AML patients and its median expression was higher compared to HD (129.26 vs 67.85, respectively; p=.019). We clustered our patients according to PALB2 expression and we defined 2 groups of patients: cluster H and L with higher and lower expression levels of PALB2, respectively (cluster centers 158.86 and 105.41, respectively; figure A). Notably, HD revealed PALB2 expression values comparable with the cluster L (range 52.90-99.60). No differences were detected in term of incidence mutations in FLT3 and NPM1, white blood cell count at diagnosis, age at diagnosis and prevalence of karyotype alterations. Patients were treated with best supportive therapy (n=11/58, therapy data missing for 2 patients), hypomethylating agents (n=2/58) and intensive chemotherapy ( n=45/58). Within patients treated with intensive chemotherapy, we compared complete remission rate after induction and we found no differences between H and L. However, patients with higher expression of PALB2 had worst overall survival than patients in cluster L (median survival group H=397 days; CI 95%=288.9-505.0, L=not reached; p=.045; figure B). Notably, we confirmed worst prognosis in patients in cluster H when considering 33 out of 45 patients with intermediate/low risk karyotype (i.e. normal karyotype, t(8;21) or less than 3 aberrations according to ELN2017; p=.026). Conclusion - We identified a subgroup of AML patients with higher expression of PALB2, which predicted poorer prognosis in patients treated with curative intent and it associated with poorer prognosis in patients with low/intermediate risk. While patients carrying mutations in PALB2 (and BRCA1/2) are candidate for PARP inhibitors (PARPi) therapies in breast cancers, few clinical trials with PARPi are available in AML and the frequency of mutations is very low. Our data opens a new scenario in which PALB2 may be a target of therapies in AML based on synthetic lethal approaches targeting the DDR pathway. However, a better understanding of the biological role of PALB2 in AML and its interaction with other alterations is needed. Supported by Fondazione Del Monte Figure. Figure. Disclosures Cavo: Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; GlaxoSmithKline: Honoraria, Membership on an entity's Board of Directors or advisory committees. Soverini:Novartis: Consultancy; Bristol Myers Squibb: Consultancy; Incyte Biosciences: Consultancy. Martinelli:Roche: Consultancy; Celgene: Consultancy, Speakers Bureau; Janssen: Consultancy; Ariad/Incyte: Consultancy; Amgen: Consultancy; Pfizer: Consultancy, Speakers Bureau; Abbvie: Consultancy; Jazz Pharmaceuticals: Consultancy; Novartis: Speakers Bureau.

Introduction Monosomy 7 (-7) and interstitial deletions of chromosome 7 (7q-) are among the most recurrent chromosomal aberrations found in myeloid neoplasms. Patients carrying these cytogenetical alterations present a poor overall survival (OS), mainly due to a low sensitivity to standard chemotherapy and a high incidence of relapse. In our study, we aimed to disentangle the biology of patients with -7/7q- and find new candidate therapeutic targets for a disease with such a dismal prognosis, by integrating wide genomic approaches. Methods We collected bone marrow samples from 487 adult patients at diagnosis, treated in 3 institutions: Institute L. & A. Seragnoli (Italy, n = 213), CEMM (Austria, n = 160), University of Michigan (US, n = 114, GSE23452). Three hundred ninety-five samples were analyzed by SNP arrays (Affymetrix™), 51 samples by mass spectrometry (Metabolon™) and 57 samples by GEP (Affymetrix™) approaches. Chi-squared, fisher's exact test and ANOVA were used to test differences in proportion and distributions. False discovery rate, Bonferroni correction, and Welch's correction were calculated whenever appropriate. Results Among the 474 patients with evaluable karyotype, 65 (13.7%) had -7/7q-; 47 (9.9%) had -7, while 18 (3.8%) had 7q-. In our sets, the median age at AML diagnosis was 64 years (21-86) and most of the subjects had a de novo AML (65.1%). WBC count at diagnosis was significantly lower in -7/7q- patients (10.4 vs 35.2 k/mm3 p Within patients tested for FLT3, NPM1 and TP53 mutation at diagnosis, 1/50 among -7/7q- patients vs 59/300 controls harbored FLT3 ITD mutation (350 patients tested, 2% vs 19.7%, p In terms of outcome, -7/7q- AML had a median of overall survival of 10.3 months (95% C.I 5.8-14.8), which accounted for 49.5 months (95% C.I. 40.5-58.4) in other AML cases. GEP data of a cohort of 57 patients (8 with -7/7q- and 49 controls) revealed that 24 genes were under-expressed in -7/7q- AML (with e-4 significance threshold, Figure 1A). Twenty-three out of 24 genes mapped on chromosome 7; one gene, COX17, mapped on chromosome 3 (Figure 1A). COX17 plays a role in the recruitment of copper to mitochondria. By metabolomic analyses, we considered quantitative data of 300 different metabolites in 32 patients (4 with -7/7q- vs 28 controls, 19 patients were excluded because samples at diagnosis were not available). In -7/7q- AML, fatty acids (sphingomyelin, 1-linoleoylglycerol), β-cytrilglutamate and the UDP were overrepresented if compared with other AML cases; on the other hand, galactiol and 1-(1-enyl-palmitoyl)-2-linoleoyl-GPC were underrepresented in -7/7q- patients. Furthermore, -7/7q- AML cells seem to accumulate 3-hydroxy-3-methylglutarate and to have lower levels of 2-Hydroxyglutarate (Figure 1C). With SNP arrays, we considered copy number alterations in 395 patients (52 -7/7q- patients vs 343 controls, Figure 1B). 5q was the most recurrent concurrent deletion, with a minimal common deleted region (MCDR) in q31.3-q33.3. Additionally, 17p (MCDR p11.2 - p13.1), 12p (MCDR p12.3-p13.1), 16q (MCDRs q11.2-q12.1, q21-q22.1 and q24.2-q24.3), 16p (MCDR p11.2) and chromosome 4 (MCDRs q34.1 and q35.2) deletions also co-occurred in -7/7q-, listed per frequencies (Figure 1B). These regions are enriched for genes controlling cell signaling, DNA transcription, post-transcriptional modifications (such as SUMOylation), mRNA splicing and cellular senescence. Conclusions SNP, GEP and metabolomic approaches gave new insights on -7/7q- AML biology, identifying 24 new genes differentially expressed in -7/7q-, and 6 MCDR associated with -7/7q- AML. Deletion of chromosome 16q and 4 were never reported in literature associated to AML. Furthermore, for the first time, we described metabolites associated with -7/7q- AML. These data may represent a useful backbone to search for candidate targets in the setting of one of the most aggressive AML subtypes. Supported by:EHA Non-Clinical Junior Research Fellowship,HARMONY,Fondazione del Monte,FP7-NGS-PTL,AIRC. *MCF and MO equally contributed &CP and GS shared the last authorship Disclosures Haferlach: MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Kralovics:MyeloPro Diagnostics and Research GmbH: Equity Ownership. Soverini:Incyte Biosciences: Consultancy; Bristol Myers Squibb: Consultancy; Novartis: Consultancy. Martinelli:Ariad/Incyte: Consultancy; Celgene: Consultancy, Speakers Bureau; Novartis: Speakers Bureau; Pfizer: Consultancy, Speakers Bureau; Amgen: Consultancy; Janssen: Consultancy; Abbvie: Consultancy; Roche: Consultancy; Jazz Pharmaceuticals: Consultancy. Cavo:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; GlaxoSmithKline: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau.

Background: The heterogeneous and poor survival group of Philadelphia negative (Ph-) B-ALL patients (pts) that doesn't have the most recurrent adult rearrangements (BCR-ABL1 t(9;22); TCF3-PBX1 t(1;19); MLL-AF4 t(4;11)) are collectively referred to as "triple negative" (Ph-/-/-) ALL. CRLF2 is frequently altered in adult B-ALL, especially in Ph-like pts (50-75% of cases). Alterations that lead, in the majority of cases, to a CRLF2 overexpression. Adult pts with CRLF2 upregulated have poor outcome and novel strategies are needed to improve it. Aims: Clustering and biological characterization of Ph-/-/- ALL (that represents 61% of adult B-ALL; Roberts KG, J Clin Oncol. 2016), considering CRLF2 overexpression event, in order to define and assess biomarkers in this subgroup to test new drugs. Patients and Methods: Gene Expression Profiling (GEP; HTA 2.0 Affymetrix) were performed on 55 Ph-/-/- ALL, 29 B-ALL Ph+ at different time point of the disease and on 7 mononuclear cell of healthy donors. Data were normalized with the Expression Console Software. Successively we cluster triple negative GEP data with our validated pipeline, based on CRLF2 upregulation and in the top ten-gene list. Ph-/-/- ALL samples were then characterized for the presence of gene fusions, Copy Number Alterations (CNAs) and mutations using different approaches (TruSight Pancancer-Illumina; MLPA and/or dMLPA-MRC-Holland; SNP Array-Affymetrix; 454 Junior-Roche and PCR). Results: Clustering our Ph-/-/- gene expression data using the impact of the 10 single genes in our cohort, we could identify a defined 2-clusters-subdivision (Gr1 and Gr2; Fig 1A). The Gr2 is characterized by CTGF, CRLF2 and CD200 (Gr2=3C-up; Fig 1B) overexpression and it represents 14.1% of all B-ALL. The Gr2 GEP is similar to Ph+ one. Fusion copy number alteration and mutational screening done, detected that 3C-Up group has a higher frequency of Ph-like associated lesions (primarily CRLF2, JAK2, IL7R mutations or deletion), that mainly affect JAK-STAT pathway. Also IKZF1 and EBF1 deletions are significantly associated to Gr2 (p=0.003; p=0.016). RAS pathway genes are highly affected in Gr1. Molecular characterization shed light on a very heterogeneous scenario especially in the group 1, suggesting the need of a more discerning clustering for this group. In spite of the small number of cases is required, preliminary Gr1 subclustering discerns MLLr and ZNF384 gene expression subgroups. Notably p53 pathway is enriched in both groups but with different deregulated genes: CHEK2 is upregulated in the group1 and CDK6 in the Gr2. CRLF2 and CD200 immunoblotting and CD200 immunohistochemistry preliminary analyses suggest that protein expression of CRFL2 and CD200 are higher in Gr2 in comparison to Gr1. Conclusions: we identified a new signature, related to CRLF2 high expression, to classify Ph-/-/- ALL B-based on 10 genes. 3C-up represents 14.1% of all B-ALL and it is characterized by a) high co-expression of three main genes: CRLF2, CTGF and CD200; b) IKZF1 deletion; c) JAK-STAT pathway mutations/fusions/deletions. Gr1 represents 46.9% of all B-ALL. Gr2 GEP similarity to Ph+ one, suggests that this Gr2 could contain Ph-like pts. This new Ph-/-/- subclassification identify new potential therapeutic targets with available drug (α-CTGF, α-CD200, CDK2, CHK2 and CDK6 inhibitors; tyrosine kinase inhibitors already effective on Ph+ and Ph-like) to test. Supported by: ELN, AIL, AIRC, project Regione-Università 2010-12 (L. Bolondi), FP7 NGS-PTL project, HARMONY project, Fondazione del Monte BO e RA project. Figure. Figure. Disclosures Cavo: Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Martinelli:Novartis: Speakers Bureau; Abbvie: Consultancy; Jazz Pharmaceuticals: Consultancy; Janssen: Consultancy; Pfizer: Consultancy, Speakers Bureau; Roche: Consultancy; Celgene: Consultancy, Speakers Bureau; Ariad/Incyte: Consultancy; Amgen: Consultancy.

Introduction Relapsed/refractory (R/R) AML patients continue to be a formidable clinical challenge, mainly in consideration of associated very poor outcome, with a median overall survival (OS) of less than 12 months. SCT represents the only curative option for these patients. Although, there is no standard-of-care approach which may serve as a bridge to SCT. Our study aims to investigate the effectiveness of MEC regimen as a rescue therapy for R/R AML patients by specifically addressing the CR rate, including minimal residual disease (MRD) negativity, the number of patients who subsequently underwent SCT and the presence of predictive factors of response. Methods Fifty-five consecutive adult AML patients were treated with MEC regimen in our Institution. In patients under 66 years old, we administered mitoxantrone 6 mg/sqm/die from day 1 to day 6, etoposide 100 mg/sqm/die from day 1 to day 6 and cytarabine 1000mg/sqm/die from day 1 to day 6, whereas in patients over 66 years old, the treatment schedule was reduced to 4 consecutive days. Data were retrospectively collected by using RedCap in accordance with Helsinki declaration and GCP. We used Kaplan-Meyer to estimate survival, and log rank to test differences in survival. Chi-squared, fisher's exact test and linear-by-linear correlation were used to test differences in proportions and distributions. Response was defined in accordance with 2017 ELN recommendations. CTCAE 4.03 was used to grade adverse events. MRD was assessed with WT1 or specific fusion transcripts. Results Fifty-five patients received MEC from 2008 to 2018. Age at diagnosis ranged from 17 to 72 years, with a median age of 51 years. Our set was enriched for high-risk patients. Interestingly, twenty percent of patients harbored FLT3-ITD at diagnosis (table 1). Two main groups were included: resistant AML, 28/55 patients (50,9%), and relapsed AML, 27/55 patients (49,1%). At induction, almost half of patients received "3+7" (n=25, 45,5%), while fludarabine-based regimens were administered to 14 patients (25,5%). In our set, after MEC median duration of hospitalization was 30 days (14-78); PMN >500/mm3 was reached after 26 days (range 18-67). Fever and febrile neutropenia was the most recurrent adverse events (AE). AEs were low in grade; out of 80 graded AEs, 38 (47,5%) were grade 2, 27 (33,8%) were grade 3, 9 (11,3%) were grade 4 and only 3 events resulted in death (3,8%). E. coli was the most recurrent cause of infection (10 cases). Overall, 25/55 patients (45,5%) achieved a complete remission (CR) after one course of MEC chemotherapy. Twelve patients (21.9%) achieved MRD negativity and 13 patients (23,6%) obtained an MRD+ CR or had no MRD test. Six patients (10,9%) had a partial response (PR) and 1 patient (1,8%)had hematological improvement (HI). Four patients (7.3%) died during post-MEC aplastic phase. Disease risk at diagnosis and R/R status did not influence the chance to obtain CR (figure 1 A). In 12 patients, a second MEC was administered. Four out of 12 patient improved their response with the 2nd MEC (2 patients obtained MRD - from MRD+ CR, 1 patient obtained PR and 1 patients obtained CR from hematological improvement). MEC was an effective bridge to SCT, 32/55 patients (58,2%, figure 1 B), received SCT; 15/32 patients (46,9%) received SCT directly after the 1st course of MEC, 9/32 patients (28,1%) after the 2nd course of MEC and 2 patients (6,3%) after an additional course of post-remission chemotherapy. Of note, only 6 patients (18,8%), who were not responsive to MEC, underwent SCT after an alternative rescue therapy. Median overall survival (OS) from MEC was 455 days (95% C.I. 307-602 days.); 1-year OS, 3-year OS and 5-years OS were 57,9%, 33,2% and 23,1%, respectively (std. error ± 0,067). Patients who responded to MEC (CR MRD+ or CR MRD- after 1 or 2 courses) had better OS than non-responders (median OS 1389 vs 160 days, p=.003). Stepwise multiple logistic regression analysis with COX-HR model established that pre-MEC R/R status, diagnosis class risk, response to one or two courses of MEC, and SCT were independent predictors of survival in the optimal model. Conclusions Taken together, our data indicate that MEC is an effective salvage regimen with affordable toxicity, and gives a high chance to obtain CR. MEC is particularly useful as a bridge to SCT, and has to be considered as a rescue therapy whenever a clinical trial is not available. *GM and AT equally contributed Disclosures Martinelli: Ariad/incyte: Consultancy; Pfizer: Consultancy; Celgene: Consultancy; Amgen: Consultancy; Janssen: Consultancy; Roche: Consultancy. Cavo:Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Introduction: Novel array-based technique-single-nucleotide polymorphism (SNP) microarray can detect cytogenetic lesions mostly involving structural alterations with losses or gains of chromosomic material. These abnormalities are predictive of response and can help define therapeutic strategies. SNP microarray can also detect copy-neutral loss of heterozygosity (CN-LOH), which has a described role in Acute Myeloid Leukemia (AML) by inducing oncogene duplication, tumor suppressor inhibition and epigenetic reprogramming. Aim: To improve conventional cytogenetic analysis and identify new genes relevant to leukemogenesis by SNP array-based genotyping. Materials and Methods: We analyzed 279 AML patients (pts) at diagnosis by SNP Array 6.0 or Cytoscan HD Array (Affymetrix). Thirty-four samples were also analyzed by Whole Exome Sequencing WES (HiSeq 2000,Illumina). SNP Array data were analyzed by Nexus Copy Number™ v7.5 (BioDiscovery) and R Development Core Team, while WES data were analyzed by GATK and MuTect. Results: Copy Number Alterations (CNAs) were scattered across all chromosomes (chrs). All pts showed CNA events: 44.4% of CN gain, 21% of CN loss and 34.6% of CN-LOH. Single copy gains mainly affected chrs X, 1, 2, 4, 9 and 8. Duplications occurred at chrs 2, 3, 5 and 14. Heterozygous loss events were detected in chrs 3, 5 and 14, while regions of deletion were located in chrs 6, 7 and 22. The CN-LOH event was the most common event and involved chrs 1, 2, 3, 4, 5, 6 and 8. We studied the deletome profile in our cohort (Fig. 1) pf pts in order to define the minimal common deletion region. SNP array analysis showed that several genes were preferentially deleted, including ADAM5 (12,9%), PHF6 (12,2%), AGPS (10%), SOX6 (7,9%), WT1 (6,5%), CRLF2 (5,4%) and LRRK1 (4,3%); while the genes preferentially amplified were GPC3 (70,25%), FLT3 (44,8%), FGF13 (36,2%), KIT (31,54%), AFF2 (31,5%), ETS1 (26,52%), MITF (22,2%), CASK (16,5%), CDY1 (14,33%), MECP2 (14,33%), FOXP2 (14%) and SMAD4 (12,9%). Single-copy losses and deletions were enriched (p Concerning single copy gain and amplified genes, the functional pathways significantly represented in our cohort were: cancer-related (103 genes), regulation of actin cytoskeleton (60 genes), MAPK signaling (64 genes), metabolic (171 genes) and cell adhesion molecules pathways (CAMs, 5 genes). Regarding gain events, 24 genes were shared by at least 42 pts (15%), 184 genes were shared by at least 14 pts (5%) and 58 genes by at least 28 pts (10%); whereas 15 genes have duplication events (in homozygosis) shared by at least 14 pts (5%). Significant CN-LOH events included genes mapping to metabolic pathways (249 genes), pathways in cancer (103 genes), regulation of actin cytoskeleton (67 genes), calcium signaling pathways (57 genes), WNT signaling pathways (51 genes) and protein digestion and absorption (34 genes). CN-LOH events in 119 genes were shared by at least 14 patients (5%). Finally, we could distinguish 3 clusters of pts, each one characterized by a peculiar pattern of amplified or deleted genes. In order to define relevant pathogenic mechanisms in our cohort, we combined the deletome profile with WES data obtained from 34 pts. Interestingly, we found deletion of genes which are also targeted by mutations (BRCA2, LRRK1). Moreover, some deleted genes, as CASK, CDK6 and MAPT, were involved in pathways affected by genomic mutations (CASK deletion and MPP6 mutation, CDK6 deletion and PPM1B mutation, MAPT deletion and SPAG5 mutation). Conclusion: By SNP array we have identified CNAs involving novel potential leukemia-related genes. Our results suggest that the comparison between SNP and WES data could provide important findings on the prognosis of AML pts. Minimal deleted regions deserve further investigation in order to identify new candidate oncogenes which could be relevant AML biomarkers. Acknowledgment: ELN, AIL, AIRC, PRIN, progetto Regione-Università 2010-12(L. Bolondi), FP7 NGS-PTL project. MCF and VG equally contributed to this work. Figure 1. Figure 1. Disclosures Soverini: Novartis, Briston-Myers Squibb, ARIAD: Consultancy. Cavo:JANSSEN, CELGENE, AMGEN: Consultancy. Kralovics:AOP Orphan: Research Funding; Qiagen: Membership on an entity's Board of Directors or advisory committees. Martinelli:BMS: Speakers Bureau; MSD: Consultancy; Roche: Consultancy; ARIAD: Consultancy; Novartis: Speakers Bureau; Pfizer: Consultancy.

Aneuploidy causes a proliferative disadvantage, mitotic and proteotoxic stress in non-malignant cells ( Torres et al. Science 2007). Chromosome gain or loss, which is the hallmark of aneuploidy, is a relatively common event in Acute Myeloid Leukemia (AML). About 10% of adult AML display isolated trisomy 8, 11, 13, 21 (Farag et al. IJO 2002), or either an isolated autosomal monosomy or monosomal karyotype (Breems et al. JCO 2008). This evidence suggests that tumor-specific mechanisms cooperate to overcome the unfitness barrier and maintain aneuploidy. However, the molecular bases of aneuploid AML are incompletely understood. We analyzed a cohort of 166 cytogenetically-characterized AML patients (80 aneuploid (A-) and 86 euploid (E-)) treated at Seràgnoli Institute (Bologna). Aneuploidy was significantly associated with poor overall survival (median survival: 13 and 26 months in A-AML and E-AML respectively; p=.006, Fig.1). To identify AML-specific alterations having a causative and/or tolerogenic role towards aneuploidy, we integrated high-throughput genomic and transcriptomic analyses. We performed 100 bp paired-end whole exome sequencing (WES, Illumina Hiseq2000) of 70 samples from our A-AML and E-AML cohort of 166 patients. Variants where called with MuTect or GATK for single nucleotide variant and indels detection, respectively. AML samples were genotyped by CytoScan HD Array (Affymetrix). Gene expression profiling (GEP) was also conducted on bone marrow cells from 24 A-AML, 33 E-AML (≥80% blasts) and 7 healthy controls (HTA 2.0, Affymetrix). We detected a significantly higher mutation load in A-AML compared with E-AML (median number of variants: 31 and 15, p=.04) which was interestingly unrelated to patients' age (median age: 63.5 years in A-AML and 62 years in E-AML, Xie et al, Nat. Med. 2014). C>A and C>T substitutions, which are likely mediated by endogenous 5mCdeamination, were the most frequent alterations (Alexandrov et al. Nat. 2013). However, aneuploidy associated with an increased variability in terms of mutational signatures, with the majority of A-AML displaying 3 or more signatures compared to few E-AML cases (p=.04). WES analysis also revealed a specific pattern of somatic mutations in A-AML. A-AML had a lower number of mutations in signaling genes (p=.04), while being enriched for alterations in cell cycle genes (p=.01) compared with E-AML. The mutated genes were involved in different cell cycle phases, including DNA replication (MCM6, PURB, SSRP1), centrosome dynamics (CEP250, SAC3D1, HEPACAM2, CCP110), chromosome segregation (NUSAP1, ESPL1, TRIOBP), mitotic checkpoint (ANAPC7, FAM64A) and regulation (CDK9, MELK, ZBTB17, FOXN3, PPM1D, USP2). Moreover, genomic deletion of cell cycle-related genes was frequently detected in A-AML. Notably, ESPL1 which associated with aneuploidy, chromosome instability and DNA damage in mammary tumors (Mukherjee et al. Oncogene 2014) was mutated and also upregulated in A-AML compared with E-AML (p=.01), the latter showing expression levels comparable to controls. Among the top-ranked genes differentially expressed between A-AML and E-AML, we identified a specific signature characterized by increased CDC20 and UBE2C and reduced RAD50 and ATR in A-AML (p Our data show a link between aneuploidy and genomic instability in AML. Deregulation of the cell cycle machinery, DNA damage and repair checkpoints either through mutations, copy number and transcriptomic alterations is a hallmark of A-AML. The results define specific genomic and transcriptomic signatures that cooperate with leukemogenic pathways, as KRAS signaling, to the development of the aggressive phenotype of A-AML and suggest that a number of A-AML patients may benefit frompharmacological reactivation of TP53pathway (e.g. MDM2 inhibitor, clinical trial NP28679). Supported by: FP7 NGS-PTL project, ELN, AIL, AIRC, PRIN, progetto Regione-Università 2010-12 GS & AP: equal contribution Disclosures Soverini: Novartis, Briston-Myers Squibb, ARIAD: Consultancy. Cavo:JANSSEN, CELGENE, AMGEN: Consultancy. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Martinelli:MSD: Consultancy; BMS: Speakers Bureau; Roche: Consultancy; ARIAD: Consultancy; Novartis: Speakers Bureau; Pfizer: Consultancy.

Introduction. Autologous Bone Marrow Transplantation (Auto-BMT) is currently rarely used in the treatment of Acute Myeloid Leukemia (AML). However, it may represent a good therapeutic option in a specific subset of patients, mainly in consolidation of both low risk (LR) and MRD negative AML without an available HLA matched donor. Aims. To review our database of AML patients who received Auto-BMT from 2005 to 2014 and who were referred to Bologna Institution, in order to assess the efficacy of the procedure in terms of Overall Survival (OS) and Disease Free Survival (DFS). Patients and methods: From 2005 to 2014, 98 AML patients underwent Auto-BMT in several Italian Institutions. 89/98 patients are evaluable for survival and outcome data. The 89 patients considered (42 female, 47 male), had a median age of 49 years (range 15-70). Cytogenetics was performed in all patients by conventional karyotype (22 patients were also analyzed by Single Nucleotide Polymorphisms Array); molecular analysis (FLT3 TKD and ITD, and NPM1 mutational analysis) was available for 51/89 patients. Molecular monitoring by specific fusion transcripts (CBF-MYH11 and AML1-ETO) was performed in CBF positive leukemias (inv(16) and t(8;21)) at the time of diagnosis, after induction, consolidation courses, and every 3 months in the first 2 years of follow-up. Based on this data, and according to ELN guidelines, a risk stratification identified 41 patients with a LR AML (t(8:21), inv(16) or NPM1+/FLT3- with normal karyotype), 4 patients with a high risk (HR) AML (complex karyotype or FLT3 ITD mutated or inv(3) or t(6;9)) and 44 patients with a standard risk (SR) AML (normal karyotype, other alterations). Results. All the patients received an induction chemotherapy treatment, as follows: a "3+7-like" course in 48 cases, a Fludarabine-based regimen in 20 patients and a Gemtuzumab-ozogamicin (GO)-based regimen in 21. 83/89 (93.3%) patients received a median of 2 consolidation courses of chemotherapy (range 1-4) before proceeding to Auto-BMT, performed in 1st CR. 6/89 (6.7%) patients received Auto-BMT in first relapse. 41 patients relapsed after auto-BMT and were treated with a re-induction chemotherapy, or were enrolled in clinical trials. 24 patients reached a 2nd complete remission, and 12 patients underwent an allogeneic BMT in 2nd CR. With a median follow up of 6 years, the median Overall Survival (OS) of the entire population was 64.3 months (range 5.8-294.2 months); the 1 year OS and the 5 years OS were, 97.1%, and 67.9%, respectively. The median Disease Free Survival (DFS) of the 83 patients treated with Auto-BMT in 1st CR was 36 months (range 1.3-293 months). The 1-year DFS and the 5-years DFS were 85% and 56.7%, respectively. Transplant related mortality (TRM, death in 100 days after BMT) was 1.2% for auto-BMT and 6.5% for allogeneic BMT. First, to assess the role of the number of consolidation courses we compared patients who received none or 1 consolidation course with patients who received 2 or more cycles, who showed a better OS (p= 0.0061, Figure 1). There was no statistical difference in terms of OS between young and elderly patients (cut off=65 years). Second, we compared patients who achieved a negative minimal residual disease status before auto-BMT (n=37) with patients who did not (n=9). MRD negativity offered a significantly better outcome in terms of 5-years OS (83.4% and 50% respectively); the median OS of MRD neg was not yet reached; the median OS of MRD pos was 27 months (p= 0.0130) (Figure 2). Conclusions: Auto-BMT offers a chance to achieve long-term DFS and OS if used as a consolidation therapy both in patients with LR and SR AML. The major role could be played in MRD negative patients, offering the best chances to achieve a long-term OS. Auto-BMT can be also a good choice as consolidation therapy for elderly patients, in which allo-BMT could induce high morbidity and mortality rates. The small patients cohort and the retrospective analysis don't allow us to define the best induction therapy to be used before auto-BMT. However, based on our findings we suggest a therapy schedule including two or more consolidation courses in patients who obtain a first CR, and to proceed then to auto-BMT. Acknowledgments: work supported by ELN, AIL, AIRC, Progetto Regione-Università 2010-12 (L.Bolondi), Fondazione del Monte di Bologna e Ravenna, FP7 NGS-PTL project. Figure 1. Figure 1. Figure 2. Figure 2. Disclosures Soverini: Novartis, Briston-Myers Squibb, ARIAD: Consultancy. Rodeghiero:Celgene Corporation: Honoraria, Research Funding. Cavo:Janssen-Cilag, Celgene, Amgen, BMS: Honoraria. Martinelli:AMGEN: Consultancy; Novartis: Consultancy, Speakers Bureau; Ariad: Consultancy; BMS: Consultancy, Speakers Bureau; ROCHE: Consultancy; Pfizer: Consultancy; MSD: Consultancy.