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The EUROPE phase 2 trial investigated the predictive value of biomarkers on the clinical efficacy of single agent romiplostim (ROM) treatment in patients with lower-risk myelodysplastic neoplasms (LR-MDS) and thrombocytopenia within the ‘European Myelodysplastic Neoplasms Cooperative Group‘ (EMSCO) network. A total of 77 patients with LR-MDS and a median platelet count of 25/nl were included, all patients received ROM at a starting dose of 750 μg by SC injection weekly. Thirty-two patients (42%) achieved a hematologic improvement of platelets (HI-P) with a median duration of 340 days. Neutrophil (HI-N) and erythroid (HI-E) responses were observed in three (4%) and seven (9%) patients, respectively. We could not confirm previous reports that HI-P correlated with baseline endogenous thrombopoietin levels and platelet transfusion history, but SRSF2 mutation status and hemoglobin levels at baseline were significantly linked to HI-P. Sequential analysis of variant allelic frequency of mutations like SRSF2 did not reveal an impact of ROM on clonal evolution in both responders and non-responders. In summary, our study confirms the safety and efficacy of ROM in LR-MDS patients and may allow to better define subgroups of patients with a high likelihood of response.

*UP, LA contributed equally Introduction A significant proportion of lower risk (LR)-MDS patients present with thrombocytopenia, being associated with shortened survival and higher risk of progression to acute myeloid leukemia (AML). Treatment options for patients with LR-MDS and severe thrombocytopenia remain limited apart from transfusion support. Romiplostim (ROM), a thrombopoietin receptor agonist (TPO-RA) has shown safety and efficacy dependent on endogenous TPO levels as well as platelet transfusion history in a poorly defined subset of LR-MDS patients (Giagounidis et al. Cancer 2014, Sekeres et al. BJH 2014). Methods The multicenter phase 2 EUROPE trial investigated potential biomarkers of response (e.g. TPO levels, molecular markers) to single agent ROM in LR-MDS patients with severe thrombocytopenia. Patients were eligible if platelet counts were ≤30 G/L or ≤50 G/L in case of bleeding history. The primary efficacy endpoint was the rate of hematologic improvement of platelets (HI-P, according to IWG 2006 criteria) lasting for at least 8 weeks after 16 weeks of ROM (750µg SC qw) treatment. At the time of screening, patients were assigned into 3 different cohorts based on their previous platelet transfusion events (PTE) as well as centrally assessed TPO serum levels (A: TPO Results From 2015 to 2019, a total of 79 patients were included at 29 trial sites in Germany, France and the Czech Republic. Patients' median age was 74 years (range 42-93), median baseline platelet count was 25.5 G/L (range 3-50 G/L) and they were stratified into cohort A (n=51) or B+C (n=28), respectively. The primary endpoint was met with 34 out of 79 (43%) patients responding (HI-P), with response being markedly higher in cohort A (49%, n=25) vs. cohort B and C (32%, n=9) (p=0.145). Ten (13%) and eight (10%) patients had additional neutrophil (HI-N) and erythroid (HI-E) responses, respectively. During treatment, six patients had transient increases in peripheral blasts to more than 10% and one patient progressed to AML after one month of ROM. Although a higher number of responders was observed in group A, neither TPO level at screening (p=0.21), nor number of pretreatment PTE (p=0.12) were significantly associated with response to ROM treatment. Thus, our findings do not confirm that baseline TPO levels and number of pretreatment PTE alone allow reliable prediction of response to ROM. With the aim to identify new molecular patterns correlating with response, we performed a targeted NGS analysis for somatic variants in 54 candidate genes in 75 patients at baseline and in 44 patients after 16 weeks of ROM. Responders (R) more frequently exhibited mutations like SRSF2 (R=39%, NR=17%), RUNX1 (R=24%, NR=14%) and TET2 (R=30%, NR=29%), whereas non-responders (NR) exhibited mutations like DNMT3A (R=12%, NR=21%), U2AF1(R=9%, NR=14%) or ASXL1 (R=6%, NR 17%) more frequent. The percentages of patients with a response to ROM were similar regardless of total number of baseline somatic mutations. Comparing responders vs. non-responders, we found no significant changes of variant allelic burden of variants detected pre- and post-ROM (Fig. 1). We identified the presence of a SRSF2 mutation as a significant predictor of response to ROM treatment (p=0.031, logistic regression). Mutated SRSF2 was significantly more frequent in responders (39%) compared to non-responders (17%) (p=0.036, Fisher's exact test) (Fig. 2A,B). We used logistic regression with stepwise backward selection to assess the influence of the presence of ASXL1, DNMT3A, RUNX1, TET2 and SRSF2 mutations on response. Our final regression model excludes the non-significant ASXL1, DNMT3A, RUNX1 and TET2 mutations and includes the significant SRSF2 mutation, resulting in an overall accuracy of 64.0% for a correct ROM response prediction in this patient cohort. Conclusion: This prospective study did not confirm a significant association between response to ROM, pretreatment PTE burden and endogenous TPO levels. Instead, patients with a mutated SRSF2 displayed a significantly higher response to ROM treatment. This may allow personalized treatment approaches in patients with LR-MDS and severe thrombocytopenia. In this study, extended treatment with ROM did not lead to a significant increase in AML cases. Disclosures Kubasch: Shire: Research Funding; Celgene: Research Funding; Novartis: Research Funding. Giagounidis:AMGEN: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees. Götze:Celgene: Research Funding. Cony-Makhoul:Novartis: Consultancy; Pfizer: Consultancy; Incyte Biosciences: Speakers Bureau; BMS: Consultancy; BMS: Speakers Bureau. Laribi:takeda: Research Funding; novartis: Honoraria, Research Funding; amgen: Research Funding; abbvie: Honoraria, Research Funding. Park:Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Other: Travel expenses. Metzeler:Astellas: Honoraria; Otsuka Pharma: Consultancy; Pfizer: Consultancy; Jazz Pharmaceuticals: Consultancy; Novartis: Consultancy; Celgene: Consultancy, Honoraria, Research Funding; Daiichi Sankyo: Honoraria. Thiede:AgenDix GmbH: Other: Co-owner and CEO. Schlenk:PharmaMar: Research Funding; Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accomodations, Expenses, Research Funding, Speakers Bureau; Novartis: Speakers Bureau; Roche: Research Funding; AstraZeneca: Research Funding; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Fenaux:Novartis: Honoraria, Research Funding; Abbvie: Honoraria, Research Funding; Jazz: Honoraria, Research Funding; BMS: Honoraria, Research Funding. Platzbecker:Novartis: Consultancy, Honoraria, Research Funding; Amgen: Honoraria, Research Funding; BMS: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Geron: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Research Funding. Ades:Abbvie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding; takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; novartis: Research Funding; Celgene/BMS: Research Funding; jazz: Membership on an entity's Board of Directors or advisory committees, Research Funding. OffLabel Disclosure: Romiplostim is a thrombopoietin receptor agonist indicated for the treatment of thrombocytopenia in patients with chronic immune thrombocytopenia (ITP). Limitations of Use: Romiplostim is not indicated for the treatment of thrombocytopenia due to myelodysplastic syndrome (MDS) or any cause of thrombocytopenia other than chronic ITP.

2509 Background: TGF-β plays a key role in regulating the tumor microenvironment. Emerging evidence suggests TGF-β is a key activator of cancer-associated fibroblasts, leading to fibrotic network development and immune exclusion. Preclinical data in murine models showed that TGF-β blockade alleviates intratumoral fibrosis, augmenting the efficacy of PD-1 immunotherapy. NIS793 is a human IgG2 mAb that binds to TGF-β. This study investigates NIS793 + spartalizumab in pts with advanced solid tumors. Methods: Pts initially received NIS793 (0.3–1 mg/kg Q3W) monotherapy; following evaluation of two dose levels, dose escalation continued with NIS793 + spartalizumab (NIS793 0.3–30 mg/kg Q3W + spartalizumab 300 mg Q3W; or NIS793 20–30 mg/kg Q2W + spartalizumab 400 mg Q4W) in pts with/without prior anti-PD-(L)1 therapy. In dose expansion, pts with non-small cell lung cancer (NSCLC) resistant to prior anti-PD-(L)1 or pts with microsatellite stable colorectal cancer (MSS-CRC) were treated at the recommended dose for expansion (RDE). Paired tumor biopsies were required from all pts. The primary objectives were to characterize safety and tolerability of the combination and determine the RDE. Results: By December 1, 2020, 60 pts were treated in the dose-escalation phase, mainly with NIS793 + spartalizumab (n = 49), and 60 pts were treated in dose expansion (MSS-CRC: n = 40; NSCLC: n = 20). Two pts were still receiving treatment. No dose-limiting toxicities were observed, and the RDE was established as 30 mg/kg (2100 mg) NIS793 + 300 mg spartalizumab Q3W. Overall 50% pts experienced ≥1 treatment-related AE (TRAE). The most common were rash (n = 15/120), pruritus (n = 10/120), fatigue (n = 9/120), and nausea (n = 8/120). Grade 3/4 TRAEs occurred in 11% pts, with rash (3%) being the most common. Treatment-related serious AEs were reported in 8 pts; 6 were grade 3/4 in severity. No deaths occurred due to AEs; 3 (2.5%) pts discontinued due to AEs. PK for NIS793 was linearly dose proportional with no obvious correlation between exposure and response. Two pts achieved a partial response (PR; one confirmed in clear cell renal cell carcinoma and one unconfirmed in NSCLC) during dose escalation of the combination. Two confirmed PRs were achieved in the MSS-CRC dose-expansion group. Biomarker data showed evidence of target engagement through increased TGF-β/NIS793 complexes and depleted active TGF-β in peripheral blood. Gene expression and protein analyses in tumor biopsies displayed decreased TGF-β target genes, decreased TGF-β signatures and increased immune signatures suggesting modulation of the TGF-β pathway and preliminary evidence of biological activity. Conclusions: Data showing target engagement and TGF-β pathway inhibition supported the proof of mechanism of NIS793. The RDE of the combination was established and well tolerated in pts with advanced solid tumors. Clinical trial information: NCT02947165.

Introduction: Myelodysplastic syndromes (MDS) are characterized by ineffective hematopoiesis and peripheral cytopenia. In about half of patients with lower-risk (LR) MDS, thrombocytopenia is present at the time of diagnosis and associated with shortened survival and an increased risk of progression to acute myeloid leukemia (AML). The thrombopoietin receptor agonist (TPO-RA) romiplostim has shown safety and marked efficacy in a still poorly-defined subset of LR-MDS patients with thrombocytopenia. Methods: The EUROPE multicenter phase 2 trial within the EMSCO network investigated the impact of biomarkers like endogenous thrombopoietin (TPO) level and platelet transfusion events (PTE) on the efficacy of romiplostim (750µg SC qw) treatment in patients with LR-MDS (IPSS low/int-1). Patients were eligible if baseline bone marrow blast count was Results: From 2015 to 2018, a total of 68 patients were included in 20 trial sites in Germany, France and Czech Republic. Patients displayed a median age of 74 years and a median platelet count of 25 G/L (range 1-50 G/L) and were stratified into cohort A (n=47), B (n=17) or C (n=4), respectively. All patients received at least one cycle of romiplostim with a median weekly dose of 750μg and a median of 15 cycles of romiplostim until week 16. Reasons for premature study discontinuation before week 16 were investigator/patient decision (n=8), adverse events (n=5), disease progression (n=4) or death (n=1). There were 9 reported severe treatment-related adverse events in seven patients including pulmonary embolism (n=1), subacute stroke (n=1), mucocutaneous hemorrhage (n=1), asthenia (n=1), suspicion of anti-romiplostim antibodies (n=1), progression to AML (n=1) and varicella zoster infection (n=1). Two patients had transient increases in peripheral blasts to more than 10% and 1 patient progressed to AML after 1 month of treatment. HI-P was observed in 26 of 68 (38%) patients, while response was ongoing in 24 of them beyond week 16. Moreover, rate of HI-P lasting for at least 8 weeks was notably higher in cohort A (45%, n=21/47) compared to patients in cohort B and C (24%, n=5/21) (p=0.11). Median peak increase of PLT count in responding patients was 199 G/L in cohort A and 83 G/L in cohort B (p=0.25) and was observed in median after 7 weeks (range 3-16). In addition, responses occurred also in 2 patients in the neutrophil (HI-N) and in 7 patients in the erythroid (HI-E) lineage according to IWG 2006 criteria (Table 1). Explorative analysis showed a correlation between pretreatment platelet transfusion requirement and endogenous TPO-levels (spearman-test, p=0.034). Median pretreatment endogenous TPO-level was lower in responders compared to non-responders (82 vs. 103 pg/ml, p=0.15). Higher response rates occurred in patients with lower TPO-levels ( Conclusion: This prospective study confirms that romiplostim treatment is highly effective in a subgroup of LR-MDS patients, but neither baseline platelet transfusion requirements nor baseline TPO levels were significantly associated with clinical response to romiplostim. Further translational analyses are ongoing to elucidate potential biomarkers of response. Disclosures Platzbecker: Celgene: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria. Götze:AbbVie: Membership on an entity's Board of Directors or advisory committees. Cony-Makhoul:Pfizer: Consultancy; Novartis: Consultancy; Incyte Biosciences: Honoraria, Speakers Bureau; BMS: Consultancy, Honoraria, Speakers Bureau. Park:Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding. Thiede:Daiichi Sankyo: Honoraria; Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; AgenDix GmbH: Employment, Equity Ownership; Diaceutics: Membership on an entity's Board of Directors or advisory committees. Ades:Helsinn Healthcare: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Silence Therapeutics: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees; Jazz: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding. OffLabel Disclosure: Romiplostim is formally not licensed for the treatment of thrombocytopenia due to myelodysplastic syndrome (MDS).

Introduction: Patients (pts) with acute myeloid leukemia (AML) who are refractory to intensive frontline treatment have a dismal outcome. In case of ineligibility for allogeneic stem cell transplantation (HSCT), the median survival of chemo-refractory AML is about 2 months and less than 5% of these pts are alive after 1-year (retrospective analysis from the AMLSG database). To date, there is no universally accepted standard approach for the treatment of chemo-refractory AML in older pts. Several retrospective studies have assessed the role of hypomethylating agents in this patient group, but complete remission (CR) rates were disappointingly low (≤10%) when compared to first line treatment. The presented study represents a novel approach focusing on hematopoietic tissue reprogramming (i.e. anakoinosis) (ClinicalTrials.gov Identifier: NCT02942758). Methods: The initial dose-finding phase I of the study evaluated the combination of azacitidine (AZA) 75 mg/d s.c. for 7 days, repeated every 28-days, pioglitazone 45 mg/d p.o. continuously from day 1 and all-trans retinoic acid (ATRA). A modified 3+3 design has been used to establish the maximum-tolerated dose of ATRA. Patients have been enrolled at an ATRA dose of 45 mg/m²/d from day 1 to day 28 and 15 mg/m²/d continuously thereafter if no dose limiting toxicity (DLT) occurred until start of next cycle on day 29. The safety DLTs were defined as toxicities attributable to ATRA, expected or unexpected, except if these are likely associated with another cause. Eligible patients had confirmed diagnosis of AML refractory to induction therapy and were not eligible for further intensive induction therapy or were not immediate candidates for allogeneic HSCT. The severity of adverse events was graded using the Common Terminology Criteria for Adverse Events (CTCAE) V. 4.03. The response to treatment was evaluated using standard criteria defined by the expert panel on behalf of the European LeukemiaNet and international working group (IWG) response. Results: Ten pts were enrolled in the safety-run-in phase I (one pt withdrew informed consent on day 9 of cycle 1). Among all treated pts, the median age was 67 years (range, 62-76 years), and the majority of pts (70%) had an ECOG PS of 1 (see table 1). Two pts had secondary AML; another two pts had therapy-related AML (t-AML). Eight pts had a complex karyotype. Concerning safety, hematological adverse events (AEs) were the most common toxicities observed. Because pts with baseline cytopenia were included (leukopenia n=8; 80%; thrombocytopenia n=9; 90%), occurrences of many hematological AEs began before study drug initiation and were attributed to underlying hematologic disease. Common 3°/4° AEs included neutropenia (50%), anemia (50%), thrombocytopenia (30%), and infections (40%). 50% of pts experienced a serious AE; one 5° AE (gastric hemorrhage) occurred. No DLTs were observed. Five pts discontinued the study, with progressive disease (PD) or relapse being the most common reason for discontinuation. Concerning efficacy, 3 pts (30%) achieved a CR and one pt a long-lasting stable disease (14 months). Morphologic review showed signs of differentiation of blasts in responding pts, which has already been shown in in-vitro analysis. In line with this observation, one pt demonstrated resolution of fungal pneumonia during the study. Conclusions: In summary, the low-intensity, biomodulatory regimen of low-dose AZA, pioglitazone, and ATRA demonstrated a tolerable safety profile and encouraging signals for efficacy in pts with AML refractory to standard induction chemotherapy warranting further investigation. S.T. and A.R. contributed equally to this abstract as senior co-authors. Disclosures Paschka: Novartis: Membership on an entity's Board of Directors or advisory committees, Other: Travel expenses, Speakers Bureau; Astellas: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees, Other: Travel expenses, Speakers Bureau; Abbvie: Other: Travel expenses; Amgen: Other: Travel expenses; Otsuka: Membership on an entity's Board of Directors or advisory committees; BMS: Other: Travel expenses, Speakers Bureau; Astex: Membership on an entity's Board of Directors or advisory committees, Travel expenses; Pfizer: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Jazz: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Other: Travel expenses; Takeda: Other: Travel expenses; Sunesis: Membership on an entity's Board of Directors or advisory committees. Döhner:Celgene, Novartis, Sunesis: Honoraria, Research Funding; AROG, Bristol Myers Squibb, Pfizer: Research Funding; AbbVie, Agios, Amgen, Astellas, Astex, Celator, Janssen, Jazz, Seattle Genetics: Consultancy, Honoraria. Thomas:Celgene: Consultancy, Other: Travel support, Research Funding, Speakers Bureau; Gilead: Membership on an entity's Board of Directors or advisory committees, Other: Travel support; Medigene AG: Consultancy, Other: Travel support; Novartis: Membership on an entity's Board of Directors or advisory committees, Other: Travel support, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Medac: Other: Travel support; Janssen: Other: Travel support.