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Plasmablastic lymphoma (PBL) is a rare entity, commonly associated with immunosuppressed states such as human immunodeficiency virus (HIV) infection or solid organ transplant. The clinical course is characterized by high relapse rates and a poor prognosis, leading some clinicians to recommend aggressive frontline therapy. However, a specific review of limited stage (LS) PBL patients is not available to evaluate outcomes and justify treatment recommendations. We performed a retrospective review of LS PBL cases to provide insight into this rare disease. Our cohort consisted of 80 stage I or II PBL patients from 13 US academic centers. With a median follow up of 34 months (1-196), the 3-year progression-free survival (PFS) and overall survival (OS) of the entire cohort were 72% (95% CI 62, 83) and 79% (95% CI 70, 89), respectively. The 3-year PFS and OS of patients treated with frontline chemotherapy alone was 65% (95% CI 50, 84) and 71% (95% CI 56, 89), respectively, compared to 85% (95% CI 72, 100) and 96% (95% CI 89, 100), respectively, in patients treated with combined frontline chemotherapy with radiation consolidation. Our data demonstrate favorable outcomes in LS PBL with no improvements in outcome from aggressive frontline treatment including Hyper-CVAD or auto-SCT consolidation. Multivariate regression analysis (MRA) demonstrated improved PFS for patients receiving EPOCH based frontline therapy versus CHOP (HR: 0.23; p = 0.029). Frontline chemotherapy followed by radiation consolidation versus chemotherapy alone appeared to be associated with improved relapse and survival outcomes but did not show statistical significance in MRA.

PURPOSE Primary or acquired resistance to cetuximab, an antiepidermal growth factor receptor monoclonal antibody (mAb), minimizes its utility in recurrent/metastatic head and neck squamous cell carcinoma (HNSCC). Aberrant hepatocyte growth factor/cMet pathway activation is an established resistance mechanism. Dual pathway targeting may overcome resistance. PATIENTS AND METHODS This multicenter, randomized, noncomparative phase II study evaluated ficlatuzumab, an antihepatocyte growth factor mAb, with or without cetuximab in recurrent/metastatic HNSCC. The primary end point was median progression-free survival (PFS); an arm met significance criteria if the lower bound of the 90% CI excluded the historical control of 2 months. Key eligibility criteria were HNSCC with known human papillomavirus (HPV) status, cetuximab resistance (progression within 6 months of exposure in the definitive or recurrent/metastatic setting), and resistance to platinum and anti–PD-1 mAb. Secondary end points included objective response rate (ORR), toxicity, and the association of HPV status and cMet overexpression with efficacy. Continuous Bayesian futility monitoring was used. RESULTS From 2018 to 2020, 60 patients were randomly assigned and 58 were treated. Twenty-seven versus 33 patients were allocated to monotherapy versus combination. Arms were balanced for major prognostic factors. The monotherapy arm closed early for futility. The combination arm met prespecified significance criteria with a median PFS of 3.7 months (lower bound 90% CI, 2.3 months; P = .04); the ORR was 6 of 32 (19%), including two complete and four partial responses. Exploratory analyses were limited to the combination arm: the median PFS was 2.3 versus 4.1 months ( P = .03) and the ORR was 0 of 16 (0%) versus 6 of 16 (38%; P = .02) in the HPV-positive versus HPV-negative subgroups, respectively. cMet overexpression was associated with reduced hazard of progression in HPV-negative but not HPV-positive disease ( P interaction = .02). CONCLUSION The ficlatuzumab-cetuximab arm met significance criteria for PFS and warrants phase III development. HPV-negative HNSCC merits consideration as a selection criterion.

BACKGROUND Management of hypopharynx cancer is often extrapolated from larynx cancer. This report analyses treatment patterns and survival limited to hypopharynx cancer using the National Cancer Database (NCDB). METHODS There are 9314 patients diagnosed with hypopharynx cancer between 2004 and 2016. The association between treatment modality and survival was analyzed using Kaplan-Meier survival curves and multivariable Cox regression. RESULTS Five-year overall survival ranged from 45% for stage I to 21% for stage IVB. Treatment modality did not influence survival in stage I/II. For stage III/IV, chemoradiation and surgery + adjuvant therapy were equivalent. Surgery yielded improved survival for T4 disease. Human papillomavirus (HPV)-positive tumors were present in 21% and were associated with improved hazard ratio of death (0.60, p =

Outcomes for patients with advanced cutaneous squamous cell carcinoma (cSCC) are poor, however recent approvals in programmed death-1 (PD-1) checkpoint inhibition have shown promise. Prior systemic treatments in this patient population included chemotherapy and anti-EGFR directed therapies, with limited long-term benefit. Studies investigating cemiplimab and pembrolizumab have recently revealed significant responses with many cases of sustained benefit in both locally advanced and recurrent and/or metastatic disease. While these treatments have shown improvement in outcomes, there are continued areas of need. This review focuses on clinical evidence for PD-1 directed checkpoint inhibition in advanced cSCC. Excluded populations and new approaches involving immunotherapy are discussed. Immune checkpoint inhibition in advanced cSCC has shown impressive benefit. The clinical trials for both cemiplimab and pembrolizumab demonstrate similar responses and outcomes. Biomarkers for predicting response are an area of need. In addition, these trials excluded immunosuppressed patients due to hematological malignancies or prior organ transplant, which are populations with significantly increased risk of cSCC. Finally, a variety of novel approaches using checkpoint inhibition in cSCC are being investigated, with some encouraging preliminary results.

BACKGROUND Salvage immunochemotherapy followed by high-dose chemotherapy and autologous stem cell transplantation is the standard-of-care second-line treatment for patients with relapsed/refractory diffuse large B-cell lymphoma after first-line R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone). Outcomes after receipt of second-line immunochemotherapy in patients with aggressive B-cell lymphomas who relapse or are refractory to intensive first-line immunochemotherapy regimens (etoposide, prednisone, vincristine, cyclophosphamide, doxorubicin, and rituximab [R-EPOCH], rituximab, hyperfractionated cyclophosphamide, vincristine, doxorubicin, and dexamethasone alternating with methotrexate and cytarabine [R-HyperCVAD], rituximab, cyclophosphamide, vincristine, doxorubicin, and high-dose methotrexate alternating with ifosfamide, etoposide, and cytarabine [R-CODOX-M/IVAC]) remain unknown. METHODS Outcomes of patients with non-Burkitt, aggressive B-cell lymphomas and relapsed/refractory disease after first-line treatment with intensive immunochemotherapy regimens who received platinum-based second-line immunochemotherapy were reviewed retrospectively. Analyses were performed to determine progression-free survival (PFS) and overall survival (OS) from the time of receipt of second-line immunochemotherapy. RESULTS In total, 195 patients from 19 academic centers were included in the study. The overall response rate to second-line immunochemotherapy was 44%, with a median PFS of 3 months and a median OS of 8 months. Patients with early treatment failure (primary refractory or relapse

Background As the number of indicated malignancies for which immune checkpoint inhibitor therapy such as pembrolizumab grows the descriptions of associated immune-related adverse events (irAEs) increases as well. On rare occasions immunotherapy can lead to development of Hemophagocytic Lymphohistiocytosis (HLH) which is a potentially lethal inflammatory disorder characterized by histiocyte activation and cytokine storm. At this time no cases of HLH developing in head and neck squamous cell carcinoma (HNSCC) patients receiving pembrolizumab have been reported. Case presentation Here we describe the first documented case of pembrolizumab-induced HLH in a 61 year-old male with metastatic HNSCC after having received multiple prior cycles of pembrolizumab without event. Following cycle 14 the patient developed fever associated with new pancytopenia and transaminitis prompting hospital admission. Infectious workup was negative, his metastatic lesions were found to be stable, and there was no evidence of new malignancy. Further workup demonstrated hyperferritinemia and bone marrow biopsy demonstrated hemophagocytosis concerning for pembrolizumab-induced HLH. Etoposide and dexamethasone therapy was initiated leading to clinical improvement and safe discharge. Conclusions Immunotherapy is a groundbreaking therapeutic intervention for patients with malignancy, however by nature of their mechanism carry a risk of inflammatory side effects. In rare circumstances these inflammatory reactions include potentially deadly syndromes such as HLH. As immunotherapeutics such as pembrolizumab become more widely utilized increased awareness of complications such as HLH is clinically relevant.

There is a paucity of data regarding outcomes and response to standard therapy in patients with limited-stage (LS) agressive B-cell lymphoma (LS-ABCL) who harbor MYC rearrangement (MYC-R) with or without BCL2 and/or BCL6 rearrangements. We conducted a multicenter retrospective study of MYC-R LS-ABCL patients who received either rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP), or more intensive immunochemotherapy (IIC) plus or minus consolidative involved-field radiation therapy (IFRT). One hundred four patients from 15 academic centers were included. Forty four patients (42%) received R-CHOP, of whom 52% had IFRT. Sixty patients (58%) received IIC, of whom 40% had IFRT. Overall response rate was 91% (84% complete response [CR]; 7% partial response). Patients with double-hit lymphoma (DHL; n = 40) had a lower CR rate compared with patients with MYC-R only (75% vs 98%; P = .003). CR rate was higher in the IFRT vs no-IFRT group (98% vs 72%; P < .001). Median follow-up was 3.2 years; 2-year progression-free survival (PFS) and overal survival (OS) were 78% and 86% for the entire cohort, and 74% and 81% for the DHL patients, respectively. PFS and OS were similar across treatment groups (IFRT vs no IFRT, R-CHOP vs IIC) in the entire cohort and in DHL patients. Our data provide a historical benchmark for MYC-R LS-ABCL and LS-DHL patients and show that outcomes for this population may be better than previously recognized. There was no benefit of using IIC over R-CHOP in patients with MYC-R LS-ABCL and LS-DHL.

Background A significant portion of diffuse large B-cell lymphoma (DLBCL) patients (35-40%) relapse or are refractory to frontline chemotherapy. The standard of care for relapsed/refractory (R/R) DLBCL patients has been salvage chemotherapy followed by consolidation with autologous stem cell transplant (ASCT) in eligible patients. Epigenetic alterations, such as aberrant DNA methylation patterns, have been linked to chemotherapy resistance in DLBCL. CC-486 is an oral hypomethylating inhibitor that inhibits DNA methyltransferase, and has provided evidence for chemotherapy sensitization in DLBCL (Clozel T, et al. Cancer Discovery, 2013). This provides rationale for addition of CC-486 to standard cytotoxic chemotherapy rituximab, ifosfamide, carboplatin, and etoposide (R-ICE) in R/R DLBCL patients who are candidates for ASCT. Here we report the results of the phase 1 trial investigating this combination. Methods Eligibility included age ≥ 18, a diagnosis of R/R DLBCL, follicular lymphoma grade 3B, or DLBCL transformed from indolent lymphoma who were candidates for salvage chemotherapy and ASCT consolidation. The study was conducted via standard 3+3 dose escalation of CC-486 at 200 mg (dose level (DL) 1), 300 mg (DL 2), and 150 mg (DL -1). A Dose limiting toxicity (DLT) was defined as grade ≥ 3 adverse event (AE) as defined by CTCAE v5 leading to ≥ 7 day delay in cycle (C) 1 or 2 of R-ICE chemotherapy as well as grade ≥ 2 vomiting/diarrhea, persisting 48 hours despite best supportive care. Patients received up to three 21-day cycles. CC-486 was given as a 7 day lead in prior to C1 and then on days 8-21 of C1 and C2 with doses held based on cytopenias/AE's per protocol. G-CSF was mandated with each cycle. The primary objective was to determine the recommended phase 2 dose (RP2D) of CC-486 in combination with R-ICE chemotherapy. Secondary objectives included overall response rate (ORR)/complete remission (CR) per 2014 IWG criteria, peripheral blood stem cell (PBSC) collection feasibility, and proportion of patients receiving ASCT consolidation. Biomarker objectives included assessment of locus specific and global methylation patterns in ctDNA at set time points. Results The study has completed accrual with enrollment of nine patients from two institutions, all of which completed planned therapy. Eight (89%) of the patients had relapsed < 1 year from completion of frontline chemotherapy. Six patients were treated at the DL1 (200 mg), three patients were treated at DL2 (300 mg), and zero patients were treated at DL-1 (150 mg) with baseline characteristics described in table 1. The most common AE's (figure 1) included nausea (78%), thrombocytopenia (78%), anemia (56%), neutropenia (55.6%), fatigue (44%), and constipation (44%). Compared with DL1, DL2 was associated with greater incidence of grade ≥ 3 hematologic AE's/cycle including neutropenia (42% v 6%), anemia (29% v 11%), and thrombocytopenia (42% v 6%); higher incidence of neutropenic fever/cycle (28.5% vs 0%); more frequent delays in day 1 of C2 or C3 of R-ICE chemotherapy (80% vs 0%); and higher rate of CC-486 doses missed in C2 and C3 due to cytopenias (40% and 4%) respectively. One DLT occurred at DL2 in a patient with grade 5 neutropenic sepsis. A planned safety review of the three patients at DL2 established that no further patients would be enrolled at this dose. No DLTs were noted in the six patients enrolled at DL1. The ORR(CR) of the 8 evaluable patients was 50%(50%) and 4/9 patients proceeded to ASCT. With a median follow up of 9.5 months (range 1.2-25.1) the median PFS and OS were 4.0 months (95% CI 2.1-NR) and 10.7 months (95% CI 9.5-NR) respectively. All 4 patients successfully collected PBSCs (defined as ≥ 3.0 x 10^6 CD34 cells/kg) with median of 4.08 x 10^6 cells/kg. Biomarker studies are pending. Discussion Patients enrolled at DL1 (200 mg) tolerated this combination well with expected hematologic AE's, no episodes of neutropenic fever, few missed doses of CC-486, no delays in R-ICE chemotherapy, and no DLTs. The CR rate was 50% and a high proportion of patients (89%) enrolled after relapsing < 1 year from completion of frontline therapy. Biomarker studies may provide information regarding DLBCL populations likely to benefit from combinations of chemotherapy and epigenetic priming. Biomarker studies related to locus specific and global methylation patterns in ctDNA will be presented at the ASH conference. Figure 1 Figure 1. Disclosures Hess: BMS: Speakers Bureau; ADC Therapeutics: Consultancy. Cerchietti: Celgene: Research Funding; Bristol Myers Squibb: Research Funding. Hill: Eli Lilly and Company: Ended employment in the past 24 months.

Background: Plasmablastic lymphoma (PBL) is a rare subtype of Non-Hodgkin Lymphoma with a well-known association with HIV infection. The outcomes of PBL patients are typically described with high relapse rates and poor prognosis. (Loghavi S, J Hematol Oncol. 2015; Morscio J, Am J of Pathol. 2014; Castillo JJ, Clin Lymphoma Myeloma Leuk. 2011; Castillo JJ, Am J Hematol. 2008) There has been a paucity of data suggesting that limited stage disease (Ann Arbor stage I-II) may have a more favorable prognosis. However, due to the rarity of this disease there have been no large-scale reviews to confirm this. Thus, many patients with limited stage disease are subject to the aggressive therapy recommendations based on the poor outcomes of PBL patients as a whole. (Loghavi S, J Hematol Oncol. 2015; NCCN Guidelines, version 2.2020; Al-Malki MM, BBMT. 2014) We attempted to determine the treatment patterns and outcomes of patients with limited stage PBL. Methods: We conducted a multi-center (13 US academic centers) retrospective study of patients with limited stage (Ann Arbor stage I-II) Plasmablastic lymphoma. Determination of limited stage and diagnosis of PBL was determined by the investigators at each individual center. Patients diagnosed between 1/1/1990 and 6/1/2018 were included. Baseline demographic, clinical, laboratory, pathology, and outcomes data were extracted by retrospective chart review. Kaplan Meier was utilized for time to event analysis. Results: Baseline characteristics are included in table 1. A total of 80 patients were identified with limited stage disease. With a median follow up of 34 months the 3-yr Progression free survival (PFS) and overall survival (OS) was 71.9% and 78.7% respectively (Figure 1A and 1B). Patients that received frontline chemotherapy with (n=29) and without RT (n=36) had a 3-yr PFS and OS of 84.6% and 96.2% as compared to 64.5% and 70.8%, respectively (Figure 2A and 2B; Figure 3A and 3B). The Hazard ratio (HR) for PFS and OS for chemo (reference) vs chemo-RT was 0.47 (95% CI 0.18-1.3; P=0.131) and 0.18 (95% CI 0.04-0.84; p=0.029) respectively. The HR for PFS and OS for CHOP (n=14, reference) vs EPOCH (n=33) based regimens was 0.37 (95% CI 0.11-1.2; p=0.106) and 0.36 (95% CI 0.079-1.6; p=0.182) respectively. Patients with stage I/IE disease (n=56) had a 3-yr PFS and OS of 73.1% and 81.2% respectively. Patients with stage II/IIE disease (n=24) had a 3-yr PFS and OS of 69.3% and 73.4% respectively. Patients that received aggressive treatment (n=17) with Hyper-CVAD based regimens and/or Auto-SCT as consolidation had a 3-yr PFS and OS of 63.6% and 72.7% respectively. Patients with concomitant HIV (n=16) had a 3-yr PFS and OS of 80.8% and 77.4% respectively. Seven patients received RT alone and 6 patients had surgical resection alone as frontline therapy; 1 patient received no therapy; 1 patient received HAART therapy only and remains in CR without any other treatment for PBL 29 months after diagnosis. There were 8 deaths (10%) related to PBL, 3 deaths (4%) related to treatment of PBL (2 during frontline chemo and 1 upon relapse with salvage chemo), and 9 deaths (11%) related to other causes. The 3-yr lymphoma free survival (LFS) of the entire cohort, pts receiving chemo alone, and pts receiving chemo-RT (without including treatment related mortality (TRM) as an event) was 89.1%, 85.2%, and 100% respectively. The 3-yr LFS survival of the entire cohort, pts receiving chemo alone, and pts receiving chemo-RT (including TRM as an event) was 85.1%, 80.0%, and 96.2% respectively. Discussion: Here we report the largest review to our knowledge of limited stage PBL. Outcomes appear to be excellent with 3-yr PFS and OS of 71.9% and 78.7% respectively and a 3-yr LFS of 89.1% (85.1% when attributing TRM as an event). There was no obvious benefit to receiving aggressive therapy with H-CVAD based regimens and/or Auto-SCT. Although this is a small, uncontrolled sample size the HR for OS was improved in patients receiving frontline chemo-RT vs chemo alone 0.18 (95% CI 0.04-0.84; p=0.029). However, this did not take into account TRM with or progression while receiving frontline chemotherapy. Patients who were HIV+ had similar PFS and OS outcomes compared to the entire cohort. This retrospective study clearly demonstrates the favorable outcomes in this patient population, especially in those able to receive definitive therapy for their disease. Disclosures Hess: ADC Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees; BMS, AstraZeneca: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Patel:Takeda: Consultancy, Research Funding; Precision Biosciences: Research Funding; Nektar: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Bristol Myers Squibb: Consultancy, Research Funding; Poseida: Research Funding; Cellectis: Research Funding; Oncopeptides: Consultancy; Janssen: Consultancy, Research Funding. Nowakowski:Nanostrings: Research Funding; Seattle Genetics: Consultancy; Curis: Consultancy; Ryvu: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other; Kymera: Consultancy; Denovo: Consultancy; Kite: Consultancy; Celgene/BMS: Consultancy, Research Funding; Roche: Consultancy, Research Funding; MorphoSys: Consultancy, Research Funding. Chavez:Bayer: Consultancy; AbbVie: Consultancy; BeiGene: Speakers Bureau; Morphosys: Consultancy, Speakers Bureau; Merck: Research Funding; AstraZeneca: Speakers Bureau; Celgene: Consultancy; Genentech: Speakers Bureau; Epizyme: Speakers Bureau; Gilead: Consultancy; Novartis: Consultancy; Kite, a Gilead Company: Consultancy, Speakers Bureau; Karyopharm: Consultancy; Verastem: Consultancy; Pfizer: Consultancy. Hill:Beigene: Consultancy, Honoraria, Research Funding; Abbvie: Consultancy, Honoraria, Research Funding; Genentech: Consultancy, Honoraria, Research Funding; Takeda: Research Funding; AstraZenica: Consultancy, Honoraria, Research Funding; Kite, a Gilead Company: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria; BMS: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Pharmacyclics: Consultancy, Honoraria, Research Funding; Karyopharm: Consultancy, Honoraria, Research Funding. Maddocks:Pharmacyclics: Consultancy, Honoraria; Morphosys: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Seattle Genetics: Consultancy, Honoraria; Karyopharm: Consultancy; ADC Therapeutics, AstraZeneca: Consultancy; BMS: Consultancy, Research Funding. Wagner-Johnston:ADC Therapeutics, Regeneron, CALIB-R, Verastem: Membership on an entity's Board of Directors or advisory committees. Kahl:AstraZeneca Pharmaceuticals LP: Consultancy, Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy; Pharmacyclics LLC: Consultancy; Genentech: Consultancy; Acerta: Consultancy, Research Funding; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene Corporation: Consultancy; ADC Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; BeiGene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche Laboratories Inc: Consultancy. Alderuccio:ADC Therapeutics: Membership on an entity's Board of Directors or advisory committees; Forma Therapeutics: Other: Family member; Agios Pharmaceuticals: Other: Family member; Oncinfo: Honoraria; Inovio Pharmaceuticals: Other: Family member; Foundation Medicine: Other: Family member; Puma Biotechnology: Other: Family member; OncLive: Honoraria. Lossos:Janssen Biotech: Honoraria; Verastem: Consultancy, Honoraria; Janssen Scientific: Consultancy, Other; Seattle Genetics: Consultancy, Other; Stanford University: Patents & Royalties; NCI: Research Funding. Portell:Bayer: Consultancy; BeiGene: Consultancy, Research Funding; Kite: Consultancy, Research Funding; Acerta/AstraZeneca: Research Funding; Amgen: Consultancy; Janssen: Consultancy; Pharmacyclics: Consultancy; AbbVie: Research Funding; TG Therapeutics: Research Funding; Infinity: Research Funding; Roche/Genentech: Consultancy, Research Funding; Xencor: Research Funding. Landsburg:Celgene: Membership on an entity's Board of Directors or advisory committees; Triphase: Research Funding; Takeda: Research Funding; Curis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Morphosys: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Speakers Bureau. Castillo:TG Therapeutics: Research Funding; Beigene: Consultancy, Research Funding; Kymera: Consultancy; Janssen: Consultancy, Research Funding; Abbvie: Research Funding; Pharmacyclics: Consultancy, Research Funding.

6015 Background: Cetuximab (C), an anti-EGFR monoclonal antibody (mAb), is approved for advanced HNSCC but benefits a minority. Crosstalk between the EGFR and hepatocyte growth factor (HGF)/cMet pathways is a known resistance mechanism. HGF is also immunosuppressive within the tumor microenvironment. A Phase I study confirmed the safety of C and ficlatuzumab (F), an IgG1 anti-HGF mAb, with preliminary efficacy and biomarker data suggesting that dual pathway inhibition may overcome tumor-intrinsic or immune cetuximab resistance. Methods: The primary objective of this phase II randomized, non-comparative trial was to evaluate the efficacy of F (20 mg/kg every 2 wks), with or without C (500 mg/m2 every 2 wks), in pan-refractory, advanced HNSCC. Eligibility criteria included recurrent/metastatic HNSCC, performance status (PS) 0-1, C resistance (defined as progression on or within 6 months of exposure), and resistance to or ineligibility for platinum and anti-PD1 mAb. Randomization was stratified by HPV status and center. The primary endpoint was median progression-free survival (mPFS). An arm was deemed worthy of further study if the lower bound of the 90% 1-sided confidence interval (CI) excluded the historical control of 2 months. Secondary objectives included overall response rate (ORR) in the overall and HPV-stratified populations. A Bayesian continuous monitoring rule for futility was applied. Results: 60 patients were randomized and 58 treated between Jan 2018 and Dec 2020 (27 to F; 33 to FC). Baseline characteristics were balanced across major prognostic variables including age, PS, HPV status, platinum resistance, and PD1 mAb exposure. Median time since prior cetuximab was 3.5 months (range 0-48 months). Grade ≥3 adverse events attributed to F included: pneumonitis (2); edema (3); diarrhea (1); LFT elevation (1); rash (2); electrolyte abnormality (2). The Table presents efficacy data. The F arm stopped for futility after 26 evaluable subjects accrued. The FC arm completed accrual and met the primary endpoint; 32 evaluable subjects had mPFS of 3.6 months (lower bound 90% 1-sided CI: 2.3 months) and ORR of 19% (6/32). All responses were in HPV- subjects, including 2 complete (CR) and 4 partial responses (PR) to the FC combination and 1 PR to F monotherapy. The mPFS and ORR for the HPV- population (n = 16) on FC were 3.8 months and 38% (6/16). Mechanistic signaling and immune biomarkers are under analysis. Conclusions: The well-tolerated FC combination met the primary PFS endpoint in pan-refractory, advanced HNSCC with notable activity in HPV- HNSCC, warranting phase III investigation. Clinical trial information: NCT03422536. [Table: see text]

Introduction Non-Small Cell Lung Cancer (NSCLC) is an aggressive malignancy with poor overall survival that accounts for up to 85% of lung cancer diagnoses. The use of immunotherapy in the form of checkpoint inhibition, to enhance the immune system's ability to attack malignant cells, has been a promising addition to treatment options in advanced NSCLC. Results Such therapeutic agents aimed at the Programmed Death 1 (PD-1) receptor or Programmed Death Ligand 1 (PD-L1) have revealed promising results against many types of cancer including NSCLC. Examples of these agents include nivolumab, pembrolizumab, BMS-936559, atezolizumab, and MEDI4736, of which the first two are approved by US FDA in the second line treatment of advanced NSCLC. Discussion Impressive improvements in objective responses from PD-1 blockade were found in both first line therapy as well as treatment after progression on platinum based therapy. In addition, the safety profile is favorable with significantly lower grade 3-4 adverse events compared to standard of care. The optimal selection criteria and factors that show an increased response to therapy are still being determined.

TPS6594 Background: Patients with pan-refractory R/M HNSCC, with clinical resistance to cytotoxic therapy, anti-EGFR molecular targeting, and immunotherapy, have poor survival. An established tumor-intrinsic resistance mechanism to cetuximab, an anti-EGFR IgG1 monoclonal antibody (mAb), is activation of the hepatocyte growth factor (HGF)/cMet pathway, which converges with the EGFR network at both the PI3K/Akt and MAPK nodes allowing for reciprocal compensation. Moreover, over-expression of HGF in the tumor microenvironment is immunosuppressive. Convergent data suggest that HGF/cMet pathway inhibition concurrent with EGFR blockade may overcome cetuximab resistance. We previously reported a Phase I study of ficlatuzumab, a humanized anti-HGF IgG1 mAb, with cetuximab in cetuximab-resistant R/M HNSCC. The combination showed promising safety, overall response rate (ORR) and progression-free survival (PFS). Preliminary biomarker analyses showed that high circulating cMet was associated with poor PFS whereas serum Veristrat, a proteomic classifier associated with worse prognosis in the setting of anti-EGFR monotherapy, was not. An increase in total peripheral T cells, particularly the CD8+ subset, was associated with treatment response while progression was associated with expansion of a unique myeloid population. We designed a follow-on randomized phase II trial evaluating ficlatuzumab with or without cetuximab in pan-refractory, R/M HNSCC with signaling and immune correlatives. Methods: This is a multicenter phase II trial with a randomized, non-comparative, two-arm design (ficlatuzumab 20 mg/kg with or without cetuximab 500 mg/m2 every 2 weeks) in patients with pan-refractory R/M HNSCC. Key eligibility criteria include: R/M HNSCC; cetuximab resistance (progression during or within 6 months of cetuximab-radiation or palliative cetuximab); platinum resistance; prior exposure to anti-PD1 mAb; ECOG 0-1; consent to baseline research biopsy. The primary objective is to evaluate the efficacy of each arm as measured by PFS. To test the hypothesis that either regimen improves historical PFS from 2 to 3.33 months requires 66 eligible patients. Key secondary endpoints are ORR and survival. Mechanistic biomarkers include tumor HGF/cMet pathway activation, tumor and peripheral immune profiles, soluble cMet, and serum Veristrat. Thirty-five of 66 subjects have enrolled at 6 centers. A Bayesian continuous monitoring rule for futility has not been triggered for either arm. Clinical trial information: NCT03422536 .

The advent of new oral anticoagulants (NOAC) has increased the armamentarium against thromboembolic diseases but has given rise to a conundrum on their reversal. NOAC's have comparable efficacy to traditional vitamin K antagonists with similar rates of major bleeding. However there is no standardized method for reversal of these agents and no specific antidote. This is of concern not only in acute bleeding episodes but also in clinical scenarios where emergency surgery is required. Recent studies have investigated reversal of dabigatran, rivaroxaban, and apixaban using prothrombin complex concentrates (PCC), recombinant factor VIIa, and in the case of dabigatran, a monoclonal antibody. These studies have been encouraging in showing improvement of bleeding times and blood loss in most models, especially with the use of PCCs and the dabigatran antibody. Of note the majority of common currently used coagulation assays may not correlate with clinical reversal. The management of overt bleeding with NOACs is difficult due to the lack of clinical trials. Current animal trials, case reports and hemostatic testing on human blood have shown some promise; provide guidance but warrant further investigation.

Introduction: Patients (pts) with limited stage (LS) aggressive large B-cell lymphoma (ALBCL) comprise 30-40% of ALBCLs and are usually treated with R-CHOP with or without consolidative involved field radiation therapy (IFRT). In pts with ALBCL, cytogenetic studies have identified a subset with high-risk disease who harbor MYC rearrangement (MYC-R) with or without BCL2 (BCL2-R) and/or BCL6 (BCL6-R) rearrangements. This has led to the adoption of intensive induction strategies in this population; however, it is unclear if such an approach is necessary in limited stage disease. Methods: We conducted a multi-center (15 US academic centers) retrospective study of MYC-R LS-ALBCL pts with diffuse large B-cell lymphoma (DLBCL) and high-grade B-cell lymphoma (HGBL) morphology. LS was defined by stage I and II confined to a single radiation field as determined by the treating center. Pts diagnosed between 1/1/2005 and 3/1/2017 were included. All pts received either R-CHOP or more intensive immuno-chemotherapy (IIC) (i.e. R-DA-EPOCH, R-hyperCVAD/MA, or R-CODOX-M/IVAC) with or without IFRT. Baseline demographic, clinical, laboratory, pathology and outcomes data was collected by retrospective chart review. Stage-modified IPI (sm-IPI) score was calculated [stage II (vs 1), age >60, elevated LDH, and ECOG performance status ≥ 2]. Differences in overall response rate (ORR), complete remission (CR) rate, 2-year progression-free survival (PFS) and overall survival (OS) were compared in pts treated with R-CHOP vs IIC and in pts treated with IFRT vs no IFRT. Results: A total of 142 pts with MYC-R LS-ALBCL were identified, of which 105 fulfilled the inclusion criteria. Baseline characteristics included: median age 65 yrs (range 21-85), 66% male; 14% stage I, 32% stage IE, 28% stage II, 26% stage IIE disease; 17% bulky, 58% extra-nodal, 15% transformed disease, 40% elevated LDH. The majority of pts (70%) had germinal center B-cell phenotype. Eighty-two pts had data on BCL2-R and BCL6-R, of which 41 (50%) had double-hit lymphoma (DHL), including 4 pts with triple-hit lymphoma. Forty-five pts (43%) received R-CHOP, of which 56% had IFRT. Sixty pts (57%) received IIC, of which 42% had IFRT. R-DA-EPOCH was the most common IIC regimen used (85%), followed by R-hyperCVAD/MA (12%). Age (p=0.38), stage (p=0.32), extra-nodal disease (p=0.84), LDH (p=0.09), sm-IPI (p=0.24), morphology (p=0.44) and double-hit status (p=1.00) were similar between pts receiving R-CHOP and IIC. Median no. of cycles (NOC) (6 vs 6) and proportion of pts who received IFRT (56% vs 42%, p=0.17) did not differ in the 2 groups. Median NOC were lower in IFRT vs no IFRT group (4 vs 6; p=0.02). Pts receiving IIC (vs. R-CHOP) were more likely to undergo CNS prophylaxis (CNS-P) (75% vs 29%, p ORR was 90% (83% CR, 7% PR). Pts with DHL were less likely to achieve a CR compared to pts with MYC-R only (73% vs 98%; p=0.011). CR rate was higher in the IFRT vs no-IFRT group (92% vs. 75%, p=0.028). In the 27 pts who had relapsed/refractory disease, distant relapses were more common in the IFRT vs no-IFRT group (87% vs 33%, p=0.007). Median follow-up was 3.2 yrs; 35 (33%) pts progressed or died. Of the 23 deaths, 15 were due to progressive lymphoma, 1 due to treatment-related toxicity and 7 due to unrelated causes. 2-year PFS and OS were 78% and 86% for the entire cohort and 72% and 82% respectively for DHL pts. Sm-IPI ≥ 2 (HR: 2.81, p=0.02) and age ≥ 70 (HR: 4.07, P Conclusions: Outcomes of MYC-R LS-ALBCL pts are excellent with 2-year PFS and OS of 78% and 86% respectively. There was no benefit of choosing IIC over R-CHOP or using CNS prophylaxis in pts with MYC-R LS-ALBCL and LS-DHL in our study. While IFRT was effective in inducing CRs and preventing local relapses, distant relapses limited its benefit. Pts with LS-DHL had lower CR rates with similar PFS and OS when compared to those with MYC-R as the sole cytogenetic abnormality. Longer follow up is needed to assess the impact of upfront treatment strategies on late relapses. Disclosures Landsburg: Takeda: Consultancy; Curis: Consultancy, Research Funding. Maddocks:Teva: Honoraria; AstraZeneca: Honoraria; Pharmacyclics/Janssen: Honoraria; Novartis: Research Funding; Pharmacyclics: Research Funding; Merck: Research Funding; BMS: Research Funding. Advani:Bayer Healthcare Pharmaceuticals: Other: Consultancy/Advisory Role; Cell Medica: Other: Consultancy/Advisory Role; Janssen Pharmaceutical: Other: Institutional Research Support; Regeneron Pharmaceuticals, Inc.: Other: Institutional Research Support; Merck: Other: Institutional Research Support; Kyowa: Other: Consulting/Advisory Role; Celgene: Other: Institutional Research Support; Roche/Genentech: Other: Consultancy/Advisory Role, Institutional Research Support; Takeda: Other: Consultancy/Advisory Role; Gilead/Kite: Other: Consultancy/Advisory Role; Autolus: Other: Consultancy/Advisory Role; AstraZeneca: Other: Consultancy/Advisory Role; Seattle Genetics: Other: Consultancy/Advisory role, Institutional Research Support; Bristol Myers Squibb: Other: Consultancy/Advisory role and Institutional Research Support; Forty Seven, Inc: Other: Institutional Research Support; Pharmacyclics: Other: Institutional Research Support; Agensys: Other: Institutional Research Support; Kura: Other: Institutional Research Support; Infinity: Other: Institutional Research Support; Millenium: Other: Institutional Research Support. Barta:Janssen: Membership on an entity's Board of Directors or advisory committees; Merck, Takeda, Celgene, Seattle Genetics, Bayer: Research Funding. Vose:Seattle Genetics, Inc.: Research Funding; Merck Sharp & Dohme Corp.: Research Funding; Novartis: Honoraria, Research Funding; Abbvie: Honoraria; Roche: Honoraria; Epizyme: Honoraria; Kite Pharma: Research Funding; Celgene: Research Funding; Incyte Corp.: Research Funding; Bristol Myers Squibb: Research Funding; Acerta Pharma: Research Funding; Legend Pharmaceuticals: Honoraria. Cohen:Takeda: Research Funding; Seattle Genetics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Millennium: Consultancy, Membership on an entity's Board of Directors or advisory committees; Janssen: Research Funding; Pharmacyclics: Consultancy, Membership on an entity's Board of Directors or advisory committees; BioInvent: Consultancy; Novartis: 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; Bristol-Myers Squibb: Research Funding; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Infinity Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees. Karmali:AstraZeneca: Speakers Bureau; Gilead: Speakers Bureau. Mehta:Seattle Genetics: Research Funding; Kite: Consultancy, Speakers Bureau; Bristol-Myers Squibb: Consultancy, Research Funding; AstraZeneca: Consultancy, Speakers Bureau; Merck: Research Funding; Spectrum: Consultancy; Epizyme: Research Funding; F. Hoffmann-La Roche Ltd: Research Funding; Incyte: Research Funding; Gilead: Consultancy, Speakers Bureau; Celgene: Consultancy; Carevive: Other: Patient engagement; Medpage: Other: Medical website. Olszewski:Spectrum Pharmaceuticals: Consultancy, Research Funding; TG Therapeutics: Research Funding; Genentech: Research Funding. Hill:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: 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; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Genentech: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics: 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; Abbvie: Honoraria, 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; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding; Seattle Genetics: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Introduction: Salvage immunochemotherapy (IC), followed by high-dose chemotherapy with autologous stem cell transplantation if chemosensitive is standard-of-care second-line (2L) therapy (tx) for fit patients (pts) with relapsed/refractory (R/R) diffuse large B cell lymphoma (DLBCL) when treated with first-line (1L) R-CHOP as shown in the CORAL study. Outcomes following receipt of salvage IC in the 2L setting for pts with DLBCL or high grade B cell lymphoma/B cell lymphoma unclassifiable (HGBL/BCLU) receiving intensive 1L tx remain unknown, and may be worse than those reported in CORAL given prior exposure to higher-dose IC in 1L setting. Here we report the results of a multicenter retrospective analysis of R/R DLBCL and HGBL/BCLU pts treated with intensive 1L tx who receive standard salvage 2L tx. Methods: Inclusion criteria were histologic diagnosis of DLBCL or HGBL/BCLU, R/R disease following 1L tx with R-EPOCH, R-HyperCVAD or R-CODOX-M/IVAC and receipt of 2L tx with R-ICE, R-DHAP, R-DHAC, R-ESHAP or R-GDP. Exclusion criteria were HIV positivity, post-transplant lymphoproliferative disorder, prior chronic lymphocytic leukemia and inadequate data. Therapy was given at the discretion of the treating physician. Progression free survival (PFS) was defined as the interval between time of first relapse or primary refractory disease and disease progression, change in therapy if no disease response or last follow-up in remission, and overall survival (OS) between time of first relapse or primary refractory disease and death or last follow-up while alive. Pts were treated from 2007-2017 and data were censored on 10/15/17. Results: A total of 195 pts treated at 20 US and Canadian academic medical centers were included. Clinicopathologic characteristics at time of R/R disease were 39% age >60 years, 62% male, 77% stage III-IV, 72% elevated LDH, 24% bone marrow (BM) involvement, 28% B symptoms present, 44% extranodal (EN) disease at >1 site, 19% ECOG performance status (PS) >1, 49% with International Prognostic Index score (IPI) ≥3, 46% HGBL/BCLU histology, 49% Ki67 ≥90%, and 61% germinal center (GCB) cell of origin (COO) by Hans algorithm. Of pts with available fluorescence in situ hybridization (FISH) data, 51%, 45% and 30% demonstrated MYC, BCL2 and BCL6 rearrangements (-R), respectively, and 37% were double hit lymphoma (DHL). Tx received in 1L were R-EPOCH in 82%, R-HyperCVAD in 16% and R-CODOX-M/IVAC in 2% of pts. R-ICE was received by 64% and other platinum-containing regimens by 36% as 2L tx. Most (86%) pts relapsed within 12 months (mo) of completion of 1L tx (early) and 58% of pts had primary refractory disease. For all pts, the median length of follow-up was 25.0 mo with a median PFS of 3.0 mo and median OS of 8.0 mo. Overall response rate to 2L tx among all pts was 44% (23% complete response [CR] and 21% partial response [PR]), and 48% with progressive disease. Pts achieving CR had significantly longer median PFS (32.0 vs 4.0 mo, p = 0.0001) and OS (not reached vs 13.0 mo, p = 0.0004) as compared to pts achieving PR. In pts who achieved CR or PR following 2L tx, 64% received consolidative transplant (42 autologous and 13 allogeneic) and achieved a median PFS and OS of 18.3 mo and 62.0 mo, respectively. As compared to pts relapsing ≥12 mo after completion of 1L tx (late), pts relapsing early were less likely to achieve CR (17% vs. 61%, p=0.0001) and experienced significantly shorter median PFS (2.8 vs. 23.0 mo, p1 site, B symptoms, ECOG PS >1 and Ki67 ≥90%, but not BCL2-R, demonstrated a statistically significant increased HR for death. Multivariate analysis demonstrated only early relapse to have a statistically significant increased HR for progression (HR 2.47, p=0.024) and death (HR 5.90, p=0.001). Conclusion: Relapse Figure. Figure. Disclosures Maddocks: Pharmacyclics: Research Funding; BMS: Research Funding; Teva: Honoraria; AstraZeneca: Honoraria; Novartis: Research Funding; Pharmacyclics/Janssen: Honoraria; Merck: Research Funding. Wagner-Johnston:Novartis: Research Funding; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; ASTEX: Research Funding; ADC Therapeutics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Research Funding; Merck: Research Funding; JUNO: Honoraria, Membership on an entity's Board of Directors or advisory committees. Karmali:Gilead: Speakers Bureau; AstraZeneca: Speakers Bureau. Kahl:Genentech: Consultancy; Juno: Consultancy; Celgene: Consultancy; Seattle Genetics: Consultancy; ADC Therapeutics: Consultancy; Gilead: Consultancy; Acerta: Consultancy; CTI: Consultancy; Abbvie: Consultancy; AstraZeneca: Consultancy. Cohen:AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Research Funding; Infinity Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Research Funding; Millennium: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics: Consultancy, Membership on an entity's Board of Directors or advisory committees; BioInvent: Consultancy; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Janssen: Research Funding; Seattle Genetics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Reddy:MEI Pharma: Research Funding. Ramchandren:Seattle Genetics: Consultancy, Research Funding; Pharmacyclics LLC an AbbVie Company: Consultancy, Research Funding; Bristol-Myers Squibb: Consultancy; Merck: Research Funding; Janssen: Consultancy, Research Funding. Diefenbach:Merck: Consultancy, Research Funding; Seattle Genetics: Consultancy, Research Funding; Incyte: Research Funding; Trillium: Research Funding; Millenium/Takeda: Research Funding; Denovo: Research Funding; Acerta: Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding; Genentech: Consultancy. Olszewski:TG Therapeutics: Research Funding; Genentech: Research Funding; Spectrum Pharmaceuticals: Consultancy, Research Funding. Barta:Janssen: Membership on an entity's Board of Directors or advisory committees; Merck, Takeda, Celgene, Seattle Genetics, Bayer: Research Funding. Hill:Novartis: 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; Genentech: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding; Seattle Genetics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, 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; Pfizer: 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; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees. Assouline:Roche: Honoraria, Research Funding, Speakers Bureau; Novartis: Research Funding; BMS: Honoraria, Research Funding, Speakers Bureau; Pfizer: Honoraria, Research Funding, Speakers Bureau; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Landsburg:Curis: Consultancy, Research Funding; Takeda: Consultancy.

This review focuses on the recent patents and use of small-molecule inhibitors (SMIs) of Bcl-2 family proteins as therapeutic agents against cancer. Bcl-2 members are crucial regulators of apoptotic cell death. Apoptosis is an evolutionarily conserved process of programmed cell death that plays an essential role in organism development and tissue homeostasis. Several mechanisms exist allowing cells to escape programmed cell death among them is the overexpression of the antiapoptotic proteins. Cancer cells are often found to overexpress many of these members such as Bcl-2, Bcl-X(L), Mcl-1, Bcl-w and A1/Bfl1 and are usually resistant to a wide range of anti-cancer drugs and treatments. Many groups have been working to develop anti-cancer drugs that block the function of anti-apoptotic Bcl-2 members, thus favoring cell death. Methods include the downregulation of Bcl-2 expression or the use of peptides or small organic molecules to the Bcl-2 binding pocket, preventing its sequestration of proapoptotic proteins such as Bid and Bim. One of the most promising aspects of SMIs in treating cancer is that their targets and mechanisms of action are different from those of cytotoxic drugs and radiation. This makes it feasible to combine SMIs with other treatments, creating a synergistic therapy, without likely development of cross-resistance or increased toxicity. A broad-spectrum or "pan" SMI which targets multiple Bcl-2 family proteins is the goal.

Control of the intrinsic apoptotic pathway is exercised through the interplay of a 20-member family of proteins related to the founding member, Bcl-2. These proteins are confined to the vicinity of two membrane surfaces, the endoplasmic reticulum and the mitochondrial outer membrane. Like most of cellular biochemistry, reactions are confined in nano time and space which do not allow the approach to equilibrium seen at the macro level of the test tube, motivating us to initiate a dynamic systems biology approach to these non-equilibrium reactions. Our laboratory has investigated the mechanism of action of a non-peptide small molecule TW-37, which represents a new chemical class of compounds like ABT-737 (Abbott) useful in the induction of apoptosis in tumor cells. The drug induces apoptotic death in lymphoma cells with an observed EC50 of 290 nM (Mohammad et al., Clin. Cancer Res.13, 2226 (2007)). TW-37 binds with nanomolar affinity to the hydrophobic groove on the surface of the pro-survival Bcl-2 proteins which can accommodate the hydrophobic face of the amphipathic α-helix of BH3-only family members such as Bid. To model how the drug perturbs the Bcl-2 system, we have immobilized a highly-helical 24-mer Bid-derived BH3-domain peptide via its N-terminus to the surface of a CM5 chip (ligand) and analyzed peptide-protein interaction with flowing analyte proteins Bcl-2, Bcl-XL, Mcl-1, Bcl-w, and Bfl-1/A1 using the Biacore 3000. Using an analysis of Langmuir binding, we observe that the analyte proteins bind Bid with ON-rates (ka) varying modestly (3.01–7.72 E+05 1/Ms), but dissociate from Bid with 17-fold variation in OFF-rate (kd). The Bcl-w complex with Bid is the slowest to dissociate with a kd of 0.0015 (1/s); the most rapid dissociation is seen with Bcl-2 and Bid, where the kd is 0.0385. We find that Bid interacts with the multidomain proteins with dissociation constants (KD) between 4 and 82 nM, intermediate between earlier determinations (J. Med. Chem.49, 6139 (2006)); Molec. Cell17, 393 (2005)), but significantly lower than the KD for the drug TW-37 and the multidomain proteins (260–1100 nM reported previously; 79-333 nM measured here). Contrary to the suggestion of Shangary and Johnson (Biochemistry41, 9485 (2002)), our BH3-mimetic TW-37 is unable to disrupt already-formed Bid heterodimers with the mutidomain survival proteins; when heterodimers on the Biacore chip are challenged with doses of TW-37 up to 10000 nM. Consequently, the only opportunity the drug might have to perturb the Bcl-2 system is to locate the hydrophobic groove before Bid. Thus, a new picture emerges of drug action in which the dynamics of pre-apoptotic protein-protein interactions creates a temporal window for drug binding to the hydrophobic groove. In this light, attempts to develop small molecule inhibitors of protein-protein interaction (Current Topics in Medicinal Chem7(10), 922–927 (2007)) should incorporate surface plasmon resonance measurements of ka and kd into preclinical drug discovery programs in addition to KD estimates of drug binding to target. Figure Figure