Abstract: Background: Several studies have indicated that the depth and duration of treatment response in multiple myeloma are both reduced in the relapsed setting. With further lines of therapy, responses continue to weaken in depth and shorten in duration. The National Comprehensive Cancer Network (NCCN) Guidelines suggest that regimens may be repeated in the relapsed setting if there has been a duration of at least 6 months since that regimen was given; however, there is limited information regarding treatment response and duration in the setting of re-treating patients with agents previously utilized. Moreover, preliminary data has suggested that carfilzomib-based regimens in the frontline may be able to attain deeper and longer responses than alternative therapies, which has led to carfilzomib being used more frequently in the frontline. This motivated us to investigate the treatment response, depth, and safety of re-challenging patients with carfilzomib in the relapsed setting. Methods: In this retrospective chart review, we identified all patients who were treated with multiple courses of carfilzomib-based regimens at Memorial Sloan Kettering Cancer Center between January 1, 2014 and November 30, 2018. Our primary objectives were to assess the response, duration of response and treatment, and safety of re-exposure to carfilzomib-based regimens. Responses were assessed as per IMWG 2016 consensus criteria (Lancet Oncol 2016). In this review we describe the clinical course, safety, and efficacy of re-challenging patients with carfilzomib in the relapsed and refractory settings. Results: Fifteen patients were identified as having received multiple, independent lines of carfilzomib-based therapy. The median age of the cohort was 58 years (49-76) with 53% male (8); two patients had R-ISS stage 1, eight stage 2, and five stage 3 disease. Five of these patients received their initial carfilzomib in the frontline as part of KRD; four of whom attained a sCR with the fifth attaining a VGPR. The remaining ten patients received their initial carfilzomib in the second-line (4) or 3rd and subsequent lines (6). Upon re-exposure to carfilzomib, patients were heavily treated with a median of four lines of therapy (2-15). All but three patients had at least one adverse cytogenetic abnormality; eight with 17p-, five with 13q-, three with t4;14, and six with 1q+. Regimens utilized in the relapsed setting included KRD (N=4), KPD (N=3), Cyklone (N=2), KD + HDAC inhibitor (N=3), KD (N=1), KCD (N=1), and KRD + daratumumab (N=1). Four patients received carfilzomib at a dose of 27 mg/m2 while the remaining 10 received 〉 36 mg/m2. Responses were seen in all but four patients (two VGPR, five PR, and four MR), with one patient experiencing progression during carfilzomib with no response; notably, this patient only attained a MR to primary carfilzomib therapy and their second exposure was the 15th line of therapy. The median time to next therapy was 4.8 months (1.9-19.4) with one patient being bridged to autologous hematopoietic cell transplantation (HCT), one to allogeneic HCT, and three are currently receiving ongoing carfilzomib treatment (13.9, 2.8, 2.5 months with VGPR, MR, and PR, respectively). Exacerbation of baseline hypertension was identified in three patients, but these instances were treated successfully with standard medications with no further complications. No additional cardiovascular events were identified in the frontline or re-treatment settings. Conclusions: We report that in a heavily pre-treated, high risk patient cohort, patients previously treated with carfilzomib-based regimens may be safely re-challenged with carfilzomib. Importantly, none of these patients experienced cardiovascular adverse effects other than exacerbation of underlying hypertension, further supporting the ability to safely re-treat a select group of patients with carfilzomib. We conclude that depending on the patient and treatment history, re-challenging with carfilzomib at relapse may be appropriate salvage therapy, particularly as a bridge towards HCT and/or clinical trials. Disclosures Hassoun: Novartis: Consultancy; Janssen: Research Funding; Celgene: Research Funding. Mailankody:Juno: Research Funding; Celgene: Research Funding; Janssen: Research Funding; Takeda Oncology: Research Funding; CME activity by Physician Education Resource: Honoraria. Lesokhin:Genentech: Research Funding; Serametrix Inc.: Patents & Royalties; Janssen: Research Funding; GenMab: Consultancy, Honoraria; BMS: Consultancy, Honoraria, Research Funding; Juno: Consultancy, Honoraria; Takeda: Consultancy, Honoraria. Smith:Celgene: Consultancy, Patents & Royalties, Research Funding; Fate Therapeutics and Precision Biosciences: Consultancy. Landau:Prothena: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding; Caelum: 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; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Karyopharm: Consultancy, Honoraria. Shah:Janssen Pharmaceutica: Research Funding; Amgen: Research Funding. Scordo:Angiocrine Bioscience, Inc.: Consultancy; McKinsey & Company: Consultancy. Giralt:Amgen: Consultancy, Research Funding; Spectrum Pharmaceuticals: Consultancy; Miltenyi: Research Funding; Jazz Pharmaceuticals: Consultancy; Actinium: Consultancy, Research Funding; Takeda: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Novartis: Consultancy; Johnson & Johnson: Consultancy, Research Funding; Kite: Consultancy. Landgren:Karyopharm: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Adaptive: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Theradex: Other: IDMC; Merck: Other: IDMC; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.

Abstract: Background: Allogeneic hematopoietic stem cell transplantation (HSCT) remains the only curative option for patients with myelofibrosis (MF). Reduced-intensity conditioning (RIC) regimens have been used to extend this therapy to older and sicker patients. Splenectomy prior to HSCT for MF has been shown to enhance neutrophil engraftment and decrease transfusion requirements, but has a reported operative mortality of 9% or higher. Splenic irradiation (sXRT) has been historically used as a palliative treatment in MF. We present our experience with a RIC regimen incorporating extracorporeal photopheresis (ECP) in combination with either pre-HSCT splenectomy or sXRT. Methods: The Tufts BMT database, the Center for International Bone Marrow Transplantation Registry (CIBMTR) database, and chart review were used to gather data. All patients underwent conditioning consisting of ECP administered on days -6 and -5, pentostatin 4mg/m2by continuous infusion over 48 hours on days -4 and -3, and a total dose of 600 cGy total body irradiation (TBI) administered in 3 fractions on days -2 and -1 (PPT). sXRT, when employed, was given in the week prior to start of PPT (days -6 to -11) with total doses ranging from 300 to 500cGy. Cyclosporine and methotrexate were used for GVHD prophylaxis. Patients surviving a minimum of six months were considered evaluable for response assessment. Complete hematologic response was defined as resolution of clinical signs of MF as well as normalization of peripheral blood counts (Hgb 〉 10gm/dL, ANC 〉 1000/µL, Platelets 〉 100K and all counts below upper limit of normal) and the absence circulating blasts. Histological response could not be assessed due to lack of follow-up bone marrow data. Clinical improvement, stable disease, progressive disease, spleen response were defined using revised IWG-MRT guidelines. Overall survival (OS) was estimated using the Kaplan Meier method from time of stem cell transplant to death. Non-relapse mortality (NRM) was estimated from time of transplant to death, treating death due to MF and relapse as competing risks. Results: Ten patients (7 females, 3 males) with MF underwent allogeneic HSCT with PPT conditioning between February 2001 and December 2012. Median age was 54 years (40-60 years). Median time from diagnosis to transplant was 48 months (6-137 months). MF was primary in 8 and secondary to essential thrombocytosis in 2 patients. According to DIPSS scoring, 1, 2, 5 and 2 patients were low, intermediate-1, intermediate-2 and high risk respectively. Donors were equally distributed between matched related and matched unrelated. Bone marrow was used as the source in all but one patient. Nine patients (90%) had palpable splenomegaly. Six underwent splenectomy of which 1 died of a related complication (sepsis from abscess in the splenic bed). Three received sXRT prior to HSCT with no associated complications. All but one patient (who had a prior splenectomy) engrafted successfully. Median time to engraftment was 18 days (sXRT 18 days, splenectomy 19 days) for neutrophils and 26 days for platelets regardless of splenic therapy. Only 2 patients developed acute grade III-IV GVHD and 1 patient developed extensive chronic GVHD. 4/7 patients with a prior splenectomy were evaluable for disease response. Of these 2 had complete hematologic response, 1 had clinical improvement with eventual relapse, and 1 had progressive disease. Among the 3 patients receiving sXRT, 2 patients had complete hematologic response as well as a spleen response and 1 had stable disease.Three patients were alive at last follow-up. Causes of death included disease relapse (n=2), GVHD (=3) and sepsis (n=2). Cumulative incidence of NRM was 40% at 1 year. Five year OS was estimated at 30%. Discussion: Our data demonstrates that splenic XRT is well tolerated and equivalent to splenectomy in terms of engraftment outcomes and disease response. Survival and GVHD outcomes with PPT conditioning were similar to those reported with other RIC regimens. PPT is a reasonable conditioning regimen for these patients. Further study to optimize timing of HSCT and patient selection to reduce NRM is needed. Disclosures Comenzo: Millennium Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Teva: Research Funding; Prothena: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau.

Abstract: 8040 Background: Passive monitoring using wearables can objectively measure sleep over extended time periods. MM patients (PTs) are susceptible to fluctuating sleep patterns due to pain and dexamethasone (dex) treatment. In this prospective study, we remotely monitored sleep patterns on 40 newly diagnosed MM (NDMM) PTs while administering electronic PT reported outcome (ePRO) surveys. The study aim was to establish sleep bioprofiles during therapy and correlate with ePROs. Methods: Eligible PTs for the study had untreated NDMM and assigned to either Cohort A – PTs 〈 65 years or Cohort B – PTs ≥ 65 years. PTs were remotely monitored for sleep 1-7 days at baseline [BL] and continuously up to 6 therapy cycles. PTs completed ePRO surveys (EORTC - QLQC30 and MY20) at BL and after each cycle. Sleep data and completed ePRO surveys were synced to Medidata Rave through Sensorlink technology. Associations between sleep measurement trends and QLQC30 scores were estimated using a linear mixed model with a random intercept. Results: Between Feb 2017 - Sep 2019, 40 PTs (21 M and 19 F) were enrolled with 20 in cohort A (mean 54 yrs, 41-64) and 20 in cohort B (mean 71 yrs, 65-82). Regimens included KRd 14(35%), RVd 12(30%), Dara-KRd 8(20%), VCd 5(12.5%), and Rd 1(2.5%). Sleep data was compiled among 23/40 (57.5%) PTs. BL mean sleep was 578.9 min/24 hr for Cohort A vs. 544.9 min/24 hr for Cohort B (p = 0.41, 95% CI -51.5, 119.5). Overall median sleep trends changed for cohort A by -6.3 min/24 hr per cycle (p = 0.09) and for cohort B by +0.8 min/24 hr per cycle (p = 0.88). EPRO data trends include global health +1.5 score/cycle (p = 0.01, 95% CI 0.31, 3.1), physical +2.16 score/cycle (p 〈 0.001, 95% CI 1.26, 3.07), insomnia -1.6 score/cycle (p = 0.09, 95% CI [-3.47, 0.26]), role functioning +2.8 score/cycle (p = 0.001, 95% CI 1.15, 4.46), emotional +0.3 score/cycle (p = 0.6, 95% CI -0.73, 1.32), cognitive -0.36 score/cycle (p = 0.44, 95% CI -1.29,0.56), and fatigue -0.36 score/cycle (p = 0.4, 95% CI -1.65, 0.93). No association between sleep measurements and ePRO were detected. Difference in sleep on dex days compared to all other days during the sample cycle period for cohort A was 81.4 min/24 hr (p = 0.004, 95% CI 26, 135) and for cohort B was 37.4 min/24 hr (p = 0.35, 95% CI -41, 115). Conclusions: Our study provides insight into wearable sleep monitoring in NDMM. Overall sleep trends in both cohorts do not demonstrate significant gains or losses, and these trends fit with HRQOL ePRO insomnia responses. Upon further examination, we demonstrate objective differences (younger PTs) in intra-cyclic sleep measurements on dex days compared to other cycle days (less sleep by 〉 1 hr). For older patients, less variation in sleep profiles was detected during dex days, possibly due to higher levels of fatigue or longer sleep duration. Sleep is an integral part of well-being in the cancer patient. Future studies should continue to characterize sleep patterns as it relates to HRQOL.

Abstract: Background and Scientific Rationale Solitary plasmacytoma of the bone (SPB) is a rare entity representing 5% of all plasma cell dyscrasias. SPB treated with radiation therapy (RT) has a 10% risk of progression to multiple myeloma (MM) over 3 years if there is no marrow involvement, whereas there is a 60% chance of progression over 3 years in patients with minimal marrow involvement. Median time to progression in the latter group is 26 months. Presently, despite mounting evidence of a significant risk of progression to MM, there is no FDA-approved therapy and patients are usually treated with localized RT. This is an area of unmet need. A similar opportunity exists in the setting of MM patients relapsing with localized disease amenable to RT. This group of patients may not immediately require long-term systemic therapy especially if RT combined with epigenetic modulation and lenalidomide results in therapeutically relevant immune responses. A few studies combining lenalidomide and azacitidine have shown responses even in a lenalidomide refractory population with upregulation of cancer testis antigen (CTA) as well as CTA specific T cell responses (Table 1). These synergistic mechanisms focus on: 1) manipulating antigen expression and enhancing antigen presentation (both neoantigens and cancer testis antigens) with oral azacitidine (CC-486), and 2) augmentation of antigen specific immune responses via increased IL2 production leading to an increase in the proliferation of T cells with lenalidomide. This combination with RT would serve to inflame the tumor microenvironment and potentially lead to therapeutically active systemic immune responses via an abscopal effect. Study Design and Methods This is an open-label, single center, single-arm study of CC-486, lenalidomide plus RT, which will enroll a total of 20 patients in two cohorts. Clinical trial registry number NCT04174196, actively recruiting. Study population and inclusion criteria Each cohort will enroll ten patients - Cohort 1: i) Histologically confirmed newly diagnosed solitary plasmacytoma of the bone or lytic bone lesion ii) Minimal marrow involvement (Detectable clonal bone marrow (BM) plasma cells by multicolor flow cytometry and ≤ 10% clonal plasma cells in a BM biopsy by immunohistochemistry, morphology, or flow cytometry) iii) Secretory M protein & lt; 3 g/dL Cohort 2: i) Relapsed multiple myeloma with plasmacytomas appropriate for RT on imaging ii) Relapsed (reappearance of M-spike/serum FLC) or progressive myeloma defined by a 25% increase from nadir in M-spike or involved serum FLC on 2 separate measurements; or with BM involvement by clonal plasma cells detectable by IHC iii) Any prior number of therapies is permitted, including prior RT iv) Allogeneic transplant patients are permitted Statistical methods We estimate the historical rate of stringent complete response (sCR) is approximately 5% (based on the rate for newly diagnosed myeloma with lenalidomide and dexamethasone on the MAIA study of 7.3% and for relapsed myeloma with Rd based on the POLLUX study of 4.6%). The primary endpoint of the study will be reported separately for the two cohorts. With 10 patients in each cohort, the maximum half-width of the exact 95% confidence interval for the response rate is +/- 0.31. A sCR rate of ≥20% would be considered promising for either cohort. Study treatment In the study, patients will be treated with CC-486 100 mg on day 1-21 and lenalidomide 25 mg on day 1-21 for 6 cycles. RT to the plasmacytoma will be initiated after cycle 2. Total dose may vary between 30-50 Gy (45-50 Gy for cohort 1) based on clinical judgement. (Figure 1) Endpoints Primary To provide preliminary efficacy data based on the rate of sCR by 2016 IMWG Criteria on post-treatment BM biopsy and aspirate specimens with no new lesions by PET. Secondary - To assess the safety of this combination. - To estimate the progression free survival and overall survival Exploratory - To evaluate antigen expression at the tumor site pre and post RT - To further characterize the antigen specific T cell response pre and post RT at the tumor site - To assess changes in epigenetic marks - To assess changes in the tumor microenvironment Disclosures Shah: Physicians Education Resource: Honoraria; Celgene/BMS: Research Funding. Mailankody:Juno Therapeutics, a Bristol-Myers Squibb Company: Research Funding; Allogene Therapeutics: Research Funding; Janssen Oncology: Research Funding; Takeda Oncology: Research Funding; PleXus Communications: Honoraria; Physician Education Resource: Honoraria. Korde:Astra Zeneca: Other: Advisory Board; Amgen: Research Funding. Hultcrantz:GSK: Research Funding; Daiichi Sankyo: Research Funding; Amgen: Research Funding; Intellisphere LLC: Consultancy. Smith:Precision Biosciences: Consultancy; Fate Therapeutics: Consultancy; Bristol Myers Squibb: Consultancy, Patents & Royalties, Research Funding. Shah:Janssen Pharmaceutica: Research Funding; Amgen: Research Funding. Lahoud:MorphoSys: Other: Advisory Board. Scordo:McKinsey & Company: Consultancy; Angiocrine Bioscience, Inc.: Consultancy, Research Funding; Omeros Corporation: Consultancy; Kite - A Gilead Company: Other: Ad-hoc advisory board. Dahi:Kite: Consultancy. Chung:Genentech: Research Funding. Hassoun:Novartis: Consultancy; Celgene: Research Funding; Takeda: Research Funding. Barker:Elekta: Research Funding; Amgen: Research Funding; Alpha Tau Medical: Other: Travel expenses, Research Funding; Merck: Research Funding. Giralt:KITE: Consultancy; MILTENYI: Consultancy, Research Funding; OMEROS: Consultancy, Honoraria; CELGENE: Consultancy, Honoraria, Research Funding; AMGEN: Consultancy, Research Funding; NOVARTIS: Consultancy, Honoraria, Research Funding; JAZZ: Consultancy, Honoraria; ACTINUUM: Consultancy, Research Funding; TAKEDA: Research Funding. Landgren:Adaptive: Consultancy, Honoraria; Takeda: Other: Independent Data Monitoring Committees for clinical trials, Research Funding; BMS: Consultancy, Honoraria; Cellectis: Consultancy, Honoraria; Glenmark: Consultancy, Honoraria, Research Funding; Juno: Consultancy, Honoraria; Seattle Genetics: Research Funding; Pfizer: Consultancy, Honoraria; Merck: Other; Karyopharma: Research Funding; Binding Site: Consultancy, Honoraria; BMS: Consultancy, Honoraria; Cellectis: Consultancy, Honoraria; Juno: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria; Merck: Other; Glenmark: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Other: Independent Data Monitoring Committees for clinical trials, Research Funding; Takeda: Other: Independent Data Monitoring Committees for clinical trials, Research Funding; Karyopharma: Research Funding; Binding Site: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Other: Independent Data Monitoring Committees for clinical trials, Research Funding; Seattle Genetics: Research Funding; Celgene: Consultancy, Honoraria, Research Funding. Lesokhin:Janssen: Research Funding; GenMab: Consultancy, Honoraria; BMS: Consultancy, Honoraria, Research Funding; Juno: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Genentech: Research Funding; Serametrix Inc.: Patents & Royalties. OffLabel Disclosure: CC-486 is an is an oral hypomethylating agent that has been studied in acute myeloid leukemia. This study combines CC-486 with lenalidomide and radiation therapy in plasma cell disorders.

Abstract: Background: BCMA targeted CAR T cell therapy has shown promising results in patients with relapsed/refractory multiple myeloma (RRMM), but relapses are common. Additional treatment options with novel therapeutic targets or mechanisms of action are needed. Here we report on the safety and efficacy of MCARH109, the first-in-class G Protein Coupled Receptor Class C Group 5 Member D (GPRC5D) targeted CAR T cell therapy (Smith EL et al. Sci. Trans Med 2019) in RRMM including patients who relapsed post BCMA targeted CAR T cell therapy. Methods: This is a phase I first-in-human, dose escalation trial of MCARH109; patients received lymphodepleting chemotherapy with fludarabine 30 mg/m 2 daily and cyclophosphamide 300 mg/m 2 daily for 3 days followed by a single infusion of MCARH109. The trial followed a standard 3+3 design with the following dose cohorts to date: 25X10 6, 50X10 6, 150X10 6, 450X10 6 viable CAR + T cells. The primary objective is to assess safety of MCARH109; secondary objectives include anti-myeloma efficacy, expansion and persistence of MCARH109 using quantitative polymerase chain reaction (qPCR) on peripheral blood and bone marrow samples. Results: 18 patients with RRMM were enrolled and underwent apheresis between September 15, 2020 and July 14, 2021. 12 patients have completed MCARH109 infusion to date, with 6 patients currently undergoing manufacturing and pending treatment. Of the 12 patients treated, median age was 59 (37-76) years and patients received a median of 8 (4-14) lines of therapy. 11 (92%) were penta-exposed, all patients were triple refractory, and 7 (58%) had prior treatment with BCMA targeted therapy including 6 (50%) who received prior BCMA CAR T therapy. 3 (25%) patients had non-secretory myeloma and 6(50%) patients had extramedullary plasmacytoma at baseline. 11 (92%) were refractory to last line of therapy and 11 (92%) patients received bridging therapy after apheresis prior to MCARH109 infusion; all patients were refractory to bridging therapy. There were no dose limiting toxicities. Cytokine release syndrome (CRS) grade 1-3 occurred in 11 (92%) patients with only one patient with grade 3 event; 4 (25%) patients received tocilizumab and 1 (8%) received dexamethasone for the treatment of CRS (Table). There were no neurologic toxicities reported to date; 3 (25%) patients had grade 1 nail changes possibly related to MCARH109 (Table). As of July 28, 2021, all treated patients have been followed for at least 2 weeks (median: 13.0 weeks; range: 2.0-39.1 weeks) and 10 (83%) had at least a minimal response or better (2 responses unconfirmed): 2 minimal response, 3 partial response, 3 very good partial response, 2 stringent complete response (sCR). 5 (56%) of the first 9 patients were minimal residual disease (MRD) negative in the bone marrow by multicolor flow cytometry (sensitivity: 10 -5). 6 (100%) patients with prior BCMA CAR T therapy had a response with 2 patients achieving sCR. We also noted robust MCARH109 expansion in the peripheral blood using qPCR across the first 3 dose levels with available data (peak expansion vector copy number/mL, median: 404,467; range: 44,670- 3,560,000; Table). With a median follow-up of 13 weeks, 9 (75%) patients are progression free and followed without additional therapy. Conclusions: MCARH109 is the first-in-class GPRC5D targeted CAR T cell therapy for MM and has a very manageable safety profile with no serious or unexpected toxicities; this dose escalation study is ongoing with additional patients planned for treatment at higher doses. Efficacy is promising in heavily pre-treated RRMM, reflected in high rates of clinical response as well as MRD-negativity, including at doses as low as 25x10 6 CAR T cells. Clinically important, all 6 patients who relapsed after BCMA CAR T therapy responded to GPRC5D targeted CAR T therapy, including 2 patients who achieved sCR. Figure 1 Figure 1. Disclosures Mailankody: Allogene Therapeutics: Research Funding; Physician Education Resource: Honoraria; Bristol Myers Squibb/Juno: Research Funding; Takeda Oncology: Research Funding; Fate Therapeutics: Research Funding; Jansen Oncology: Research Funding; Evicore: Consultancy; Legend Biotech: Consultancy; Plexus Communications: Honoraria. Shah: Janssen: Research Funding; Celgene/BMS: Research Funding. Lesokhin: pfizer: Consultancy, Research Funding; Iteos: Consultancy; Trillium Therapeutics: Consultancy; Genetech: Research Funding; Serametrix, Inc: Patents & Royalties; bristol myers squibb: Research Funding; Janssen: Honoraria, Research Funding; Behringer Ingelheim: Honoraria. Korde: Medimmune: Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding. Hassoun: Celgene, Takeda, Janssen: Research Funding. Hultcrantz: GlaxoSmithKline: Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Research Funding; Daiichi Sankyo: Research Funding; Intellisphere LLC: Consultancy; Curio Science LLC: Consultancy. Shah: Amgen: Research Funding; Janssen: Research Funding. Landau: Takeda, Janssen, Caelum Biosciences, Celgene, Pfizer, Genzyme: Membership on an entity's Board of Directors or advisory committees; Takeda: Research Funding; Genzyme: Honoraria. Scordo: Angiocrine Bioscience: Consultancy, Research Funding; Omeros Corporation: Consultancy; Kite - A Gilead Company: Membership on an entity's Board of Directors or advisory committees; i3 Health: Other: Speaker; McKinsey & Company: Consultancy. Roshal: Auron Therapeutics: Other: Ownership / Equity interests; Provision of services; Celgene: Other: Provision of services; Physicians' Education Resource: Other: Provision of services. Landgren: Janssen: Other: IDMC; Janssen: Honoraria; Janssen: Research Funding; Amgen: Honoraria; Celgene: Research Funding; Amgen: Research Funding; Takeda: Other: IDMC; GSK: Honoraria. Dogan: Physicians' Education Resource: Honoraria; Seattle Genetics: Consultancy; Peer View: Honoraria; Takeda: Consultancy, Research Funding; Roche: Consultancy, Research Funding; EUSA Pharma: Consultancy. Giralt: Actinnum: Membership on an entity's Board of Directors or advisory committees; JENSENN: Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees; AMGEN: Membership on an entity's Board of Directors or advisory committees; CELGENE: Membership on an entity's Board of Directors or advisory committees; PFIZER: Membership on an entity's Board of Directors or advisory committees; JAZZ: Membership on an entity's Board of Directors or advisory committees; SANOFI: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees. Park: Autolus: Consultancy; Kite Pharma: Consultancy; PrecisionBio: Consultancy; Minerva: Consultancy; Curocel: Consultancy; Intellia: Consultancy; Amgen: Consultancy; Affyimmune: Consultancy; Innate Pharma: Consultancy; Novartis: Consultancy; Servier: Consultancy; Kura Oncology: Consultancy; Artiva: Consultancy; BMS: Consultancy. Rivière: FloDesign Sonics: Other: Provision of Services; Juno Therapeutics: Patents & Royalties; The Georgia Tech Research Corporation (GTRC): Other: Provision of Services (uncompensated); Centre for Commercialization of Cancer Immunotherapy: Other: Provision of Services; Fate Therapeutics: Other: Provision of Services, Patents & Royalties. Brentjens: BMS: Consultancy, Patents & Royalties, Research Funding; Gracell Biotechnologies, Inc: Consultancy, Ended employment in the past 24 months; sanofi: Patents & Royalties; Caribou: Patents & Royalties. Smith: Eureka Therapeutics: Consultancy; Fate Therapeutics: Research Funding; Chimeric Therapeutics: Consultancy; Novarits: Consultancy; Sanofi: Patents & Royalties: GPRC5D antibody based therapies; BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties: CAR T cells for MM. OffLabel Disclosure: MCARH109 is an experimental GPRC5D targeted CART therapy

Abstract: Background: Patients treated with cytotoxic chemotherapies and/or autologous stem-cell transplantation (ASCT) are at risk for therapy-related myeloid neoplasms (tMN). As these agents yield increased mutation burden in relapsed malignancies and leave evidence of exposure via mutational signatures, we studied the genomic and temporal relationship between chemo exposure and progression of clonal hematopoiesis (CH) to tMN. Methods: We analyzed 32 tMN whole genomes (WG) from 31 patients [27 acute myeloid leukemias (AML), 4 myelodysplastic syndromes]. For 7 patients with tMN post-high-dose melphalan/ASCT, we investigated the presence of antecedent CH using targeted sequencing (MSK-IMPACT; Bolton et al. Nat Gen 2020) on pre-melphalan blood mononuclear cells, granulocytes, or CD34+ apheresis samples. Results: TMN was diagnosed a median of 4.2 years (IQR, 2.6-6.6) following primary treatment. When compared to data from 200 de novo AML from TCGA (NEJM, 2013), tMNs had fewer mutations in FLT3 (9.7% v 28.0%; p = 0.028) and NPM1 (3.2% v 27.0%; p = 0.003). TP53 loss was enriched in tMNs (25.8% v 10.5%; p = 0.035 ). Mutational signature analysis revealed 5 known single base substitution (SBS) signatures in tMN: the hematopoietic stem-cell (SBS-HSC), aging (SBS1), melphalan (SBS-MM1), and platinum signatures (E-SBS1, E-SBS20) (Rustad et al. Nat Comm 2020, Pich et al. Nat Gen 2019). Complex structural variants (SV), defined as ≥3 breakpoint pairs involved in simultaneous copy number changes (Rustad et al. Blood Can Disc 2020), were observed in 7 tMNs; including chromothripsis in 6 tumors (19.4%), chromoplexy in 2 (6.5%), templated insertion in 1 (3.2%), and unspecified complex SV in 2 (6.5%). Chromothripsis has not been previously reported in de novo AML and, in 4 cases, involved chromosome 19 with hyper-amplification of the SMARCA4 locus (≥5 copies). CH variants that became clonal in tumor were seen in 5/7 pre-melphalan/ASCT samples and included mutations in TP53, RUNX1, NCOR1, NF1, CREBBP, DNMT3A, and PPM1D. Chemotherapy introduces hundreds of mutations, leaving each exposed cell with a unique catalogue (i.e., barcode). In fact, TMNs with evidence of chemo signatures had a higher mutation burden (median 1574 single nucleotide variants) than those without (median 938; p = 0.004). Detection of chemo signatures in bulk genome sequencing relies on one cell, with its catalogue of mutations, to expand to clonal dominance (Fig 1a, Landau et al. Nat Comm 2020). Given the long latency between exposure and tMN diagnosis, this single-cell expansion model was expected for all samples exposed to melphalan or platinum-based regimens (i.e., agents with a measurable signature). Strikingly, all patients with pre-tMN platinum exposure (n=7) had evidence of platinum SBS signatures whereas only 2 of 7 patients with prior melphalan/ASCT had a melphalan signature (SBS-MM1). As all platinum-exposed tMN had mutational evidence of exposure, a CH clone must have existed prior to exposure, supporting a single-cell expansion model. Absence of a chemo signature for 5/7 post-melphalan/ASCT tumors despite exposure implies tumor progression driven either by multiple clones in parallel (Fig 1b) or by an unexposed clone. As latency largely excludes the former, this suggests pre-tMN CH clones were re-infused during SCT, thus avoiding chemo exposure (Fig 1c). This is supported by two lines of evidence: 1) tMNs from 2 patients exposed to sequential platinum and melphalan/ASCT had platinum but not melphalan signatures confirming single-cell expansion of the pre-tMN CH clone post-platinum but with escape from exposure to melphalan in the ASCT (Fig 1d); 2) targeted sequencing of pre-tMN samples from melphalan/ASCT patients identified tMN genomic mutations at the CH level in 5/7 cases, including in all 3 tested apheresis samples - one of which (TP53) expanded to dominance without a melphalan signature. Conclusion: WG sequencing identified novel features of tMN revealing the key driver role of complex SV. Mutational signature analyses and targeted sequencing of pre-tMN samples can increase our understanding of tMN pathogenesis and demonstrate that tMNs arising post-ASCT are often driven by CH clones that re-engraft after escaping melphalan exposure. This mode of expansion suggests that a permissive, immunosuppressed, post-transplant environment might play a more important role than chemotherapy-induced mutagenesis in tMN pathogenesis. Figure 1 Figure 1. Disclosures Diamond: Sanofi: Honoraria; Medscape: Honoraria. Watts: Rafael Pharmaceuticals: Consultancy; Genentech: Consultancy; Bristol Myers Squibb: Consultancy; Takeda: Consultancy, Research Funding; Jazz Pharmaceuticals: Consultancy; Aptevo Therapeutices: Research Funding. Kazandjian: Arcellx: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees. Bradley: AbbVie: Consultancy, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Bolli: Amgen: Honoraria; Takeda: Honoraria; Janssen: Consultancy, Honoraria; Celgene/BMS: Consultancy, Honoraria. Papaemmanuil: Isabl Technologies: Divested equity in a private or publicly-traded company in the past 24 months; Kyowa Hakko Kirin Pharma: Consultancy. Scordo: Kite - A Gilead Company: Membership on an entity's Board of Directors or advisory committees; i3 Health: Other: Speaker; Omeros Corporation: Consultancy; Angiocrine Bioscience: Consultancy, Research Funding; McKinsey & Company: Consultancy. Lahoud: MorphoSys: Membership on an entity's Board of Directors or advisory committees. Stein: Jazz Pharmaceuticals: Consultancy; Foghorn Therapeutics: Consultancy; Blueprint Medicines: Consultancy; Gilead Sciences, Inc.: Consultancy; Abbvie: Consultancy; Janssen Pharmaceuticals: Consultancy; Genentech: Consultancy; Celgene: Consultancy; Bristol Myers Squibb: Consultancy; Agios Pharmaceuticals, Inc: Consultancy; Novartis: Consultancy; Astellas: Consultancy; Syndax Pharmaceuticals: Consultancy; PinotBio: Consultancy; Daiichi Sankyo: Consultancy; Syros Pharmaceuticals, Inc.: Consultancy. Sauter: Precision Biosciences: Consultancy; Kite/Gilead: Consultancy; Bristol-Myers Squibb: Research Funding; GSK: Consultancy; Gamida Cell: Consultancy; Celgene: Consultancy, Research Funding; Genmab: Consultancy; Novartis: Consultancy; Spectrum Pharmaceuticals: Consultancy; Juno Therapeutics: Consultancy, Research Funding; Sanofi-Genzyme: Consultancy, Research Funding. Hassoun: Celgene, Takeda, Janssen: Research Funding. Mailankody: Bristol Myers Squibb/Juno: Research Funding; Physician Education Resource: Honoraria; Plexus Communications: Honoraria; Takeda Oncology: Research Funding; Jansen Oncology: Research Funding; Fate Therapeutics: Research Funding; Allogene Therapeutics: Research Funding; Legend Biotech: Consultancy; Evicore: Consultancy. Korde: Medimmune: Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding. Hultcrantz: Daiichi Sankyo: Research Funding; Intellisphere LLC: Consultancy; Curio Science LLC: Consultancy; GlaxoSmithKline: Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Research Funding. Shah: Bristol Myers Squibb: Research Funding; Janssen: Research Funding. Shah: Janssen Pharmaceutica: Research Funding; Amgen: Research Funding. Park: Servier: Consultancy; Affyimmune: Consultancy; Autolus: Consultancy; Minerva: Consultancy; PrecisionBio: Consultancy; BMS: Consultancy; Novartis: Consultancy; Kura Oncology: Consultancy; Curocel: Consultancy; Artiva: Consultancy; Innate Pharma: Consultancy; Intellia: Consultancy; Amgen: Consultancy; Kite Pharma: Consultancy. Landau: Genzyme: Honoraria; Takeda, Janssen, Caelum Biosciences, Celgene, Pfizer, Genzyme: Membership on an entity's Board of Directors or advisory committees; Takeda: Research Funding. Sekeres: BMS: Membership on an entity's Board of Directors or advisory committees; Takeda/Millenium: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees. Ho: Blueprint Medicine: Membership on an entity's Board of Directors or advisory committees. Roshal: Celgene: Other: Provision of services; Auron Therapeutics: Other: Ownership / Equity interests; Provision of services; Physicians' Education Resource: Other: Provision of services. Lesokhin: pfizer: Consultancy, Research Funding; Janssen: Honoraria, Research Funding; Iteos: Consultancy; Serametrix, Inc: Patents & Royalties; Genetech: Research Funding; Trillium Therapeutics: Consultancy; bristol myers squibb: Research Funding; Behringer Ingelheim: Honoraria. Morgan: BMS: Membership on an entity's Board of Directors or advisory committees; Jansen: Membership on an entity's Board of Directors or advisory committees; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees. Landgren: Janssen: Other: IDMC; Janssen: Research Funding; Amgen: Honoraria; Celgene: Research Funding; Janssen: Honoraria; Amgen: Research Funding; Takeda: Other: IDMC; GSK: Honoraria. Maura: OncLive: Honoraria; Medscape: Consultancy, Honoraria.