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Abstract Background: Venetoclax, a small-molecule inhibitor of B cell leukemia/lymphoma-2, in combination with hypomethylating agents (HMA) has shown improved efficacy and survival benefit compared to HMA alone (DiNardo et al, 2020) in elderly/unfit patients with acute myeloid leukemia (AML). Since FDA-approval of this regimen for elderly/unfit AML patients, it is frequently utilized both in the upfront and relapsed/refractory setting. Cardiac events with venetoclax are not well described. In the VIALE-E trial, which included patients ineligible for standard induction chemotherapy due to congestive heart failure or stable angina, 15% of patients receiving azacitidine plus venetoclax experienced atrial fibrillation as a serious adverse event, vs. 1% in the azacitidine plus placebo group (DiNardo et al, 2020). Our objective was to provide an estimate of the prevalence of and a description of all cardiac events that occurred in AML patients undergoing treatment with venetoclax + HMA. Methods: 170 consecutive patients with AML who received venetoclax +HMA (azacitidine or decitabine) outside the context of a clinical trial between 1/2017-11/2020 at the Mayo Clinic were included. Patients received venetoclax + HMA either as upfront treatment or for relapsed/refractory disease. Patients with relapse following allogeneic stem cell transplant were excluded. We evaluated all cardiac events that occurred while treatment with venetoclax + HMA was ongoing. Baseline patient and treatment characteristics were compared using the Mann-Whitney U-test and the Fisher's exact test. All statistics were computed using EZR (Version 1.53). Results: 1. Patient characteristics A total of 170 patients who received venetoclax + HMA (median age 69 years [range 17-91], 63% males) were included. ELN risk category was either adverse risk (48%, 82/170) or intermediate risk (48%, 82/170) in the majority of patients. 64% (109/170) of patients received venetoclax + HMA as upfront treatment. Characteristics including age, ELN cytogenetic risk, cardiovascular risk factors, and upfront vs relapsed therapy were similar among patients with or without cardiac events. The only exception was a higher incidence of CEBPA mutation amongst those with cardiac events (12% vs 2%, p=0.03). The majority (83%, 141/170) of patients underwent an echocardiogram prior to initiation of therapy. 2. Cardiac events Of 170 patients treated with venetoclax + HMA during the study period, 34 (20%) patients experienced a total of 48 cardiac events. Of patients experiencing cardiac events, 32% (11/34) had no pre-existing cardiac disease and 12% (4/34) had no cardiovascular risk factors (Table 1). The majority of events occurred early in treatment course: 41% during cycle 1, 26% during cycle 2 and 15% during cycle 3 (Table 1). The most frequently occurring cardiac event (21%, 10/48 events) was a decrease in left ventricular ejection fraction on echocardiography, which was associated with symptoms in all ten patients. Second most frequent was atrial fibrillation with rapid ventricular response at 17% (8/48 events), followed by troponin elevation without electrocardiogram changes at 15% (7/46 events). Of patients with troponin elevation, 57% (4/7 events) occurred in the setting of another inciting factor such as severe anemia, while 43% represented a troponin elevation without explanation (Table 1). Other cardiac events included heart failure with preserved ejection fraction (n=4), other symptomatic arrhythmia (n=4), and symptomatic pericardial effusion or pericarditis (n=3). In addition, 2 of 34 (6%) patients experienced fatal cardiopulmonary arrest. The majority (88%) of cardiac events required either inpatient admission (62%, 21/34 patients) or intensive care unit (ICU) care (26%, 9/34 patients). 77% of patients required new cardiac medications or procedural intervention (n=4). In 27% of cases (9/34 patients), the cardiac event directly contributed to death (Table 1). Conclusions: Cardiac complications were observed in one-fifth (20%) of AML patients treated with venetoclax + HMA, despite the absence of preexisting cardiac disease in a third of cases; moreover 27% of events were fatal. Further comparative studies are required to identify salient clinical features predictive of cardiac complications in these patients. Figure 1 Figure 1. Disclosures Al-Kali: Novartis: Research Funding; Astex: Other: Research support to institution. Litzow: Astellas: Research Funding; Amgen: Research Funding; Omeros: Other: Advisory Board; AbbVie: Research Funding; Actinium: Research Funding; Pluristem: Research Funding; Jazz: Other: Advisory Board; Biosight: Other: Data monitoring committee. Patnaik: Kura Oncology: Research Funding; StemLine: Research Funding.

Abstract Background: trALL is an important secondary primary malignancy (SPM) that has recently been appreciated. While patients (pts) with MM have an 8%-17% risk of developing an SPM while on lenalidomide (R) maintenance following autologous stem cell transplant (ASCT), trALL has been rarely observed. Little is known about the characteristics of trALL in pts with MM compared to pts who had other malignancies prior to the development of trALL. We define tALL as any prior exposure to cytotoxic chemotherapy and/or radiation for another malignancy, and herein, we report a comparative analysis of characteristics and outcomes of pts with trALL with and without MM from the Mayo Clinic Cancer Center (MCCC). Methods: We performed a systematic search in the 3-site MCCC registry and included all pts diagnosed and received at least 1 cycle of ALL-directed therapy and/or underwent allogeneic transplantation (AlloHCT) for ALL between 2007-2020. All cases of trALL in this series are B-ALL. Comparisons of characteristics between trALL patients with and without MM were made using a Wilcoxon rank sum test (continuous variables) or Fisher's exact test (categorical variables). Time-to-event variables were compared using unadjusted Cox proportional hazards regression models. Results: 70 trALL pts (14 MM [20%], 56 non-MM [80%]) were identified during the study period. The median age at trALL diagnosis was 63.9 (range 47-71) for MM pts and 63.1 (range 18.2-84) for non-MM pts. Median follow-up from trALL diagnosis was 1.42 years (range 0.02-10.6 years). The most common prior non-MM malignancies among tALL pts were breast (28.6%), lymphoma (17.9%), myeloid (17.9%), and GU/GYN (14.3%). Amongst the 14 MM pts, 100% (n=10) had ISS-I disease, 8 (57%) had IgG K MM, 1 (n=10) had high risk cytogenetics, 8 (57.1%) received R-based induction , 4 (28.6%) received CyBorD induction, 4(28.6%) received VRD induction, 3 (21.4%) received RD induction. 10 (71.4%) pts were actively on R when they developed trALL, 8 (57.1%) pts received prior ASCT. The median time to develop trALL following ASCT for MM was 46.3 months (m), (95% CI 20.4-67.6), 12 (85.7%) pts received R maintenance with a median duration of 53m (95% CI 16.9-121). The median time to develop trALL after initiation of R maintenance was 61.2m (95% CI 16.9-123.4). The most common trALL induction regimen received was HyperCVAD which was used in 71.4% of MM pts and 51.8% of non-MM pts. In comparison to non-MM pts, MM patients had a significantly lower WBC at diagnosis (Median: 2.0 vs. 5.8, P=0.005),no t(9;22) BCR/ABL1 cytogenetics (0.0% vs. 35.7%, P=0.008), a higher frequency of hypodiploid/near-triploid (Ho-Tri) cytogenetics (42.9% vs. 12.5%, P=0.009), and a lower frequency of prior radiation therapy (7.1% vs. 44.6%, P=0.012). MM pts had a higher frequency of AlloHCT for trALL (71.4% vs. 42.9%, P=0.075) and were more commonly in complete response (CR) at transplant (100.0% vs. 70.8%, P=0.078). No trALL in MM pts were Ph-like ALL. There was a statistically significant difference in time to development of trALL between previous malignancy locations (P=0.018), with GU/GYN (Median: 9 years) having the longest time and myeloid (Median: 3 years) having the shortest time; MM was 6 years. In the overall pt cohort, 56 (80%) pts achieved a complete response after induction and 60% (n=25) were minimal residual disease (MRD)+ after induction. Pts with MM had a significantly lower likelihood of being MRD+ after induction (OR=0.09, P=0.015). Overall, 24.3% of pts relapsed after induction therapy for trALL; 39 (55.5%) died after trALL diagnosis including 43% (n=35) who died after AlloHCT. Although pts with MM tended to have better outcomes compared to non-MM trALL pts in terms of overall survival after trALL diagnosis (Figure 1A), survival after AlloHCT (Figure 1B), relapse rate after trALL diagnosis and non-relapse mortality after AlloHCT, none of these findings were statistically significant in this small cohort (Figure 1C). Conclusion: trALL is a unique SPM that can occur in pts with MM. It is associated with Ho-Tri cytogenetics and is BCR/ABL1 negative. The majority of MM pts that developed trALL had undergone prior ASCT and were on R maintenance when they developed trALL. Despite being more likely to have adverse cytogenetics features, MM-associated trALL has similar survival compared to non-MM-associated trALL which speaks to the poor survival outcomes of this SPM. Further research on trALL in MM pts is merited. Figure 1 Figure 1. Disclosures Litzow: Amgen: Research Funding; Pluristem: Research Funding; AbbVie: Research Funding; Actinium: Research Funding; Astellas: Research Funding; Omeros: Other: Advisory Board; Jazz: Other: Advisory Board; Biosight: Other: Data monitoring committee. Bergsagel: Janssen: Consultancy. Fonseca: Scientific Advisory Board: Adaptive Biotechnologies: Membership on an entity's Board of Directors or advisory committees; Caris Life Sciences: Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy; Patent: Prognosticaton of myeloma via FISH: Patents & Royalties; Bayer: Consultancy; Takeda: Consultancy; Celgene: Consultancy; Amgen: Consultancy; BMS: Consultancy; Mayo Clinic in Arizona: Current Employment; Juno: Consultancy; Kite: Consultancy; Aduro: Consultancy; OncoTracker: Consultancy, Membership on an entity's Board of Directors or advisory committees; GSK: Consultancy; Novartis: Consultancy; Merck: Consultancy; Sanofi: Consultancy; Pharmacyclics: Consultancy; Janssen: Consultancy. Dispenzieri: Takeda: Research Funding; Alnylam: Research Funding; Pfizer: Research Funding; Oncopeptides: Consultancy; Sorrento Therapeutics: Consultancy; Janssen: Consultancy, Research Funding. Murthy: CRISPR Therapeutics: Research Funding. Ailawadhi: GSK: Consultancy, Research Funding; Sanofi: Consultancy; Pharmacyclics: Consultancy, Research Funding; Takeda: Consultancy; Medimmune: Research Funding; Xencor: Research Funding; Genentech: Consultancy; Janssen: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Cellectar: Research Funding; Beigene: Consultancy; BMS: Consultancy, Research Funding; AbbVie: Consultancy; Karyopharm: Consultancy; Ascentage: Research Funding. Foran: actinium: Research Funding; taiho: Honoraria; bms: Honoraria; servier: Honoraria; pfizer: Honoraria; novartis: Honoraria; OncLive: Honoraria; abbvie: Research Funding; boehringer ingelheim: Research Funding; takeda: Research Funding; trillium: Research Funding; aptose: Research Funding; revolution medicine: Honoraria; syros: Honoraria; sanofi aventis: Honoraria; certara: Honoraria; gamida: Honoraria; kura: Research Funding; h3bioscience: Research Funding; aprea: Research Funding; sellas: Research Funding; stemline: Research Funding.

Abstract Background: Therapy-related acute myeloid leukemia (AML) is a well-described entity and known to carry a worse prognosis, compared to de novo AML. In the current study, we sought to describe the presenting features and outcome of patients with AML, in the setting of previous history of cancer with or without exposure to chemotherapy or radiotherapy. Methods: A Mayo Clinic database of patients with AML was queried to identify patients with a previous history of cancer, both hematologic and solid tumors. A comparative analysis of presenting features, treatment details and survival were performed between patients with therapy-related AML (Group A) and those with AML and a history of cancer that had been managed with surgery alone (Group B). Results: A total of 250 patients (median age 68 years, range 19-90; 60% males) with AML and a previous history of cancer (both hematologic and solid) were identified; 182 (73%) cases were determined to be therapy-related AML (Group A) while the remaining 68 (27%) did not receive chemotherapy or radiotherapy for their antecedent cancer (Group B) (Table). Among group A patients 106 (58%) were exposed to chemotherapy, 37 (20%) to radiotherapy and 39 (22%) to combination chemotherapy and radiotherapy for their cancer. At the time of AML diagnosis, adverse karyotype was noted in 91 (51%) group A and 12 (19%) group B patients (p<0.0001); the incidence of adverse karyotype in patients exposed to chemotherapy vs radiotherapy alone vs combined chemoradiotherapy was 54% (57/106), 30% (11/37), and 59% (23/39) respectively (p=0.04). Group A patients, compared to those in group B, included more females (46% vs 24%; p=0.001), and more preceding hematologic malignancies (p=<0.0001). Next generation sequencing was performed in 74 patients and the results showed no significant difference between groups A and B (Table). Treatment and outcome in Groups A and B: Intensive and less intensive AML-directed chemotherapy were given to 100 (55%) and 44 (24%) patients in group A and 38 (56%) and 14 (21%) patients in group B (P=0.8). 79 (65%) remissions (complete remission (CR) 42 (29%) and CR with incomplete count recovery (CRi) 37 (26%) were documented in Group A and 37 (71%) remissions (CR: 21 (40%) and CRi=16 (31%) in Group B (P=0.2). After a median follow-up of 8.4 months (range: 0.9-217), 184 deaths were documented: 132 (72.5%) in Group A and 52 (76.5%) in Group B (P=0.5). 52 (36%) patients from Group A and 25 (48%) from Group B relapsed (P=0.1). The median (range) overall survival (OS) rates of patients from Group A was 13 (9-17) months and that of Group B was 14 (10-35) months (P=0.6). The 1-, 3- and 5-year OS rates were 52%, 28%, and 24% in Group A; and 62%, 33%, and 24% in Group B patients (Fig 1). Multivariable analysis identified relapse (HR 2.8, 95% CI 1.7-4.7) and failure to achieve CR/CRi (HR 2.8 95% CI 1.9-4.7) as risk factors for inferior survival (Fig 2a and 2b). The median (range) relapse free survival of patients in Group A was 28 (17 -81) and that of Group B was 27 (14 - 76) months (P=0.9) (Fig 2c). 28 patients underwent allogenic stem-cell transplant (25 in CR1 and 3 in CR2), 23 in Group A and 5 in Group B; the 1-, 3-, and 5-year OS of patients who underwent allogenic stem cell transplant were 88%, 72%, and 72% regardless of the group (Fig 2d). Conclusion: The current study did not find significant differences between AML patients with previous history of cancer with or without exposure to chemo/radiotherapy, in terms of either response to AML-directed therapy or overall or relapse-free survival, despite a higher prevalence of adverse karyotype in therapy-related AML. Figure 1 Figure 1. Disclosures Patnaik: Kura Oncology: Research Funding; Stemline Therapeutics: Membership on an entity's Board of Directors or advisory committees; Stemline Therapeutics: Membership on an entity's Board of Directors or advisory committees. Al-Kali: Astex: Other: Research support to institution; Novartis: Research Funding. Litzow: Pluristem: Research Funding; Actinium: Research Funding; AbbVie: Research Funding; Astellas: Research Funding; Amgen: Research Funding; Jazz: Other: Advisory Board; Omeros: Other: Advisory Board; Biosight: Other: Data monitoring committee.

Abstract Background: Relapsed or refractory (R/R) acute lymphoblastic leukemia (ALL) or lymphoblastic lymphoma (LL) remain a therapeutic challenge, especially in elderly patients(pts) or those with T-cell immunophenotype. Inhibition of apoptosis is an increasingly recognized mechanism for resistance to conventional chemotherapy. Recently, the oral bcl-2 inhibitor venetoclax (VEN) has shown remarkable activity in a variety of hematologic malignancies. Preclinical data in both B- and T-ALL suggests synergy of VEN with vincristine(VCR). Liposomal VCR (L-VCR) is FDA approved for relapsed ALL having progressed following 2 or more antileukemia therapies. We designed a phase I/II trial (EA9152) of the combination of L-VCR and VEN for pts with r/r B-or T-cell ALL or LL. Here, we report for the first time the safety and efficacy outcomes of the phase I portion of this trial (NCT03504644). Methods: This open-label phase I/II study enrolled pts age>=18 with ALL or LL who were R/R to multiagent chemotherapy. Subjects could have received prior VCR or VEN . In a standard 3 + 3 dose escalation design, subjects were given a two week lead-in phase of single agent VEN in the following schedule: dose level 1 - 20, 50, 100, 200 mg on days 1, 2, 3, 4 and 400 mg on days 5 ‒ 42; dose level 2 - 50, 100, 200, 400 mg on days 1, 2, 3, 4 and 600 mg on days 5 ‒ 42; and dose level 3 ‒ 100, 200, 400, 600 mg on days 1, 2, 3, 4 and 800 mg on days 5 ‒ 42. Weekly L-VCR 2.25mg/m 2 IV was started on D15 of cycle 1, and starting day 1 for subsequent cycles (cycle 2+ = 28 days). For cycle 2 and beyond, VEN 400mg, 600mg, or 800mg based on dose level was given starting on day 1 of the cycle. Primary objective of the phase I portion was to determine the maximum tolerated dose (MTD) of VEN in combination with L-VCR. Secondary objectives included determining preliminary response rates. Results: EA9152 was activated on April 26, 2018 and the phase I portion closed to accrual on March 2, 2021. Among the 18 pts in dose escalation (Table 1), the median age was 42 years (22-77). The majority of pts were male (56%), white (80%), and with a performance status (PS) of 1 (78%). Among 13 pts with disease diagnosis reported, 9 had ALL and 4 had LL. Seventeen of 18 (94%) reported previous chemotherapy, two of which had previous stem cell transplant. Median treatment cycles received is 1 (range 1-11). One patient, having received 11 cycles, remains on study at the time of data analysis. Grade >=3 treatment-related adverse events were reported in 89% of treated pts, with neutrophil count decreased (67%), white blood cell decreased (56%), and anemia (50%) as the most common. One pt experienced grade 3 tumor lysis syndrome. Twelve pts were considered evaluable for MTD determination. Six pts were considered not evaluable for toxicity analysis on account of withdraw of consent for treatment (n=4) or rapid disease progression (n=2). Two pts (2 of 3) at dose level 3 experienced DLTs, one each of hypokalemia and heart failure. Therefore, the MTD of the combination was determined to be dose level 2 - VEN 50, 100, 200, 400 mg on days 1, 2, 3, 4 and 600 mg on days 5 ‒ 42 and for subsequent cycles, with L-VCR 2.25mg/m2 IV weekly. In regards to best overall responses observed (Table 2) 4 of 18 pts (22%) achieved complete response (CR), 4 patients (22%) had stable disease, and 7 (39%) had progressive disease. Two patients in CR were found to be measurable residual disease (MRD) negative as well. Conclusions: In the phase 1 portion of this study, the combination of VEN and L-VCR was found to be safe for patients with ALL and LL. The MTD of the combination was found to be VEN 600mg daily with encouraging preliminary efficacy seen including MRD negative responses. The phase 2 portion of this trial is actively enrolling with VEN 600mg daily starting C1D1. Figure 1 Figure 1. Disclosures Palmisiano: Takeda: Consultancy; Genentech: Research Funding; Foundation One: Consultancy; AbbVie: Consultancy, Research Funding. Claxton: Astellas: Other: Clinical Trial; Novartis: Research Funding; Astex: Research Funding; Cyclacel: Research Funding; Daiichi Sankyo: Research Funding; Incyte: Research Funding. Park: BMS: Consultancy; Amgen: Consultancy; Autolus: Consultancy; Novartis: Consultancy; Minerva: Consultancy; PrecisionBio: Consultancy; Curocel: Consultancy; Artiva: Consultancy; Kite Pharma: Consultancy; Kura Oncology: Consultancy; Affyimmune: Consultancy; Servier: Consultancy; Innate Pharma: Consultancy; Intellia: Consultancy. Podoltsev: Novartis: Honoraria; Incyte: Honoraria; Celgene: Honoraria; Pfizer: Honoraria; Blueprint Medicines: Honoraria; Bristol-Myers Squib: Honoraria; PharmaEssentia: Honoraria; CTI BioPharma: Honoraria. Atallah: Novartis: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Research Funding; BMS: Honoraria, Speakers Bureau; Takeda: Consultancy, Research Funding; Abbvie: Consultancy, Speakers Bureau; Amgen: Consultancy. Dinner: Kite/Gilead: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria. Webster: AmGen: Consultancy; Pfizer: Consultancy. Luger: Syros: Honoraria; Agios: Honoraria; Daiichi Sankyo: Honoraria; Jazz Pharmaceuticals: Honoraria; Brystol Myers Squibb: Honoraria; Acceleron: Honoraria; Astellas: Honoraria; Pfizer: Honoraria; Onconova: Research Funding; Celgene: Research Funding; Biosight: Research Funding; Hoffman LaRoche: Research Funding; Kura: Research Funding. Litzow: AbbVie: Research Funding; Astellas: Research Funding; Amgen: Research Funding; Actinium: Research Funding; Pluristem: Research Funding; Jazz: Other: Advisory Board; Omeros: Other: Advisory Board; Biosight: Other: Data monitoring committee. OffLabel Disclosure: Venetoclax, a BCL-2 inihibitor, is not FDA-approved for use in ALL.

Abstract Introduction: Therapy-related myeloid neoplasm (t-MN) includes acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), and myelodysplastic/myeloproliferative neoplasms (MDS/MPN) that occur as a complication of DNA-damaging therapies. The World Health Organization recommends considering t-MN as a single entity. Whether t-MDS and t-AML have distinct characteristics and outcomes is not known. The aim of this study was to compare clinicopathological characteristics and outcomes of t-MDS and t-AML. Methods: All patients diagnosed with t-MN based on the World Health Organization criteria were identified. Bone marrow biopsies, cytogenetic, and next-generation sequencing (NGS) were obtained at the treating physician's discretion. Pathogenic/likely pathogenic variants (PV) were called based on the standard criteria. Overall survival (OS) was calculated from the time of t-MN diagnosis until the last follow up using Kaplan-Meier analysis using Wilcoxon test. For survival analysis comparing chemotherapy to best supportive care (BSC) only, patients were censored at the time of allogeneic stem cell transplant (SCT). Multivariate analysis was performed using Cox proportional hazard method and corrected using false discovery rate (FDR). Statistical analysis was performed using JMP (v14.1, SAS Institute) and significance was defined as P<0.05. Results: We identified 554 patients, of which 180 (32.4%), 365 (65.8%), and 9 (1.6%) presented as t-AML, t-MDS, and t-MDS/MPN respectively. t-MDS/MPN patients were excluded from further analysis due to a small number. Clinical and laboratory characteristics of the t-AML and t-MDS cohorts is shown in Table 1. t-AML patients were significantly more anemic and thrombocytopenic at presentation. As expected, t-AML had a higher peripheral blood and BM blast count. There was no difference in proportion of patients with chromosomal abnormalities, though a statistically significantly higher proportion of t-MDS patients had chromosome 5 abnormality, 5q deletion, monosomy 5, chromosome 7 abnormality, monosomy 7 compared to t-AML patients. On other hand, 11q23 (mixed lineage leukemia, MLL) rearrangement was more common in t-AML compared to t-MDS (9.3% vs. 2.8%, P=0.005). A higher proportion of t-MDS patients had PV detected by NGS compared to t-AML (92.9% vs. 85.6%, P=0.038). A higher proportion of t-MDS patients had PV in TP53 (37.6% vs. 21.4%, P=0.004) and ASXL1 (23% vs. 11.7%, P=0.016) genes; whereas a higher proportion of t-AML patients had PV in RAS (18.9% vs. 9.1%, P=0.013) and WT1 (8.1% vs. 2.9%, P=0.05) genes. One hundred twenty-eight (35%) of 365 t-MDS patients progressed to t-AML. The presence of any chromosomal abnormality at t-MDS diagnosis predicted a higher risk of transformation to t-AML (χ 2 3.9, P=0.03). t-AML patients had a significantly shorter OS compared to t-MDS (9.2 vs. 19.7 months, P<0.0001, Figure A). This difference persisted when stratified by no disease modifying therapies (BSC only) 2 vs. 17 months (P<0.0001, Figure B), as well as among those who received at least one line of chemotherapy (14 vs. 24.6 months, P<0.001). Finally, a higher proportion of patients with t-AML underwent SCT and there was a trend towards improved survival for t-AML patients (vs. t-MDS 52.9 vs. 20.7 months, P=0.07) from the time of transplant. Multivariate analysis for OS performed to control for all the variables that were different at presentation (except for blast count), showed that t-MDS (as opposed to t-AML) phenotype at diagnosis, and undergoing SCT were independent predictors of improved survival (Table 2). Conclusion: t-MDS and t-AML have distinct clinical, cytogenetic, and genetic features at presentation. In the absence of disease modifying therapies, t-AML is a more aggressive phenotype, consistently associated with a shorter survival. Even after controlling adverse risk features, t-AML phenotype had a shorter survival compared to t-MDS. Figure 1 Figure 1. Disclosures Litzow: AbbVie: Research Funding; Astellas: Research Funding; Amgen: Research Funding; Actinium: Research Funding; Pluristem: Research Funding; Jazz: Other: Advisory Board; Omeros: Other: Advisory Board; Biosight: Other: Data monitoring committee. Hiwase: Novartis: Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees.

Abstract Background: DDX41 gene is located on chromosome 5q35 and is believed to be a tumor suppressor gene involved in splicing of mRNA. Mutated DDX41 have been identified as germline mutation (m) in families with cases of myeloid neoplasm and have shown to cause acquisition of other somatic mutations resulting in MDS/AML. At the same time, somatic pathogenic DDX41 mutations are known to occur. Variant of unknown significance (VUS) is an intermediate tier between benign and pathogenic (path) mutations (hence uncertain) and can be re-classified based on their clinical impact. In this report we analyzed the clinical impact and relevance of DDX41VUS in patients (pts) being evaluated for myeloid disorders. Methods: We reviewed 4,524 consecutive pts who underwent NGS (MC OncoHeme 42 genes panel) testing between 2018 and 2021 performed on cases of suspected or known myeloid disorders. We identified 58 (1%) consecutive pts with DDX41VUS, among them one pt had proven concurrent DDX41 germline VUS and 7 pts with DDX41VUS had concurrent DDX41path mutation. We analyze clinical characteristics of pts with DDX41VUS and compared it with cohort of 32 DDX41path mutated pts. Results: Baseline characteristics are summarized in Table 1, and Figure 1 illustrates DDX41VUS per case with variant allele frequency (VAF) and observed concurrent mutations. The median VAF for DDX41 VUS was 48 % (range, 14-91%). Co-mutations were found in 14 (28%) pts with VUS, and the reminder (n=44, 72 %) had isolated DDX41VUS. Among them AML (16 [32%]), MDS (14 [28%]), cytopenia (14 [28%]) MPN (3 [6%]), CNL (1 [2%]) and aplastic anemia (1 [2%]) were the commonly occurring myeloid disorder (Table 1, Figure 1). Eleven of 14 pts with isolated cytopenia had isolated DDX41VUS. Conversely, among 15 evaluable pts with isolated DDX41VUS, 13 (87%) pts had normal cytogenetics and 40% of pts had family history of solid or hematological malignancies. We observed a significant difference in hematologic diagnoses: DDX41VUS patients were significantly less often diagnosed with MDS or CCUS, and more often associated with cytopenias NOS. Recurrent, non-random DDX41VUS sequences were observed; most frequent occurring amino acid change among the 58 pts were Gly173Arg (n=6), Met155lle (n=5), Pro258Leu (n=3) Arg479Gln (n=3), Val303Met (n=2), Lys331del (n=2), Arg479His (n=2) and Tyr33His (n=2) (Figure 1). 5 of 6 pts with Gly173Arg had isolated DDX41VUS, and among them 4 were diagnosed with MDS suggesting this could be a clonal event, and possible driver mutation, notable in Figure 1. The median overall survival (OS) of pts with high risk MDS/AML harboring DDX41VUS was not reached (60% alive at 2 years). Between pts with DDX41path and DDX41VUS, proportion of pts with co-mutations (p >0.99), cytogenetic abnormalities (p >0.99), family history of malignancies (p 0.52), time to treatment (p >0.99), MDS progression to AML (p 0.36) and OS (among high risk MDS/AML pts) (p 0.55) was not significantly different, suggesting that phenotypic features of DDX41VUS are similar to DDX41path , and that both carry a similar, more indolent prognosis (Table 1). Conclusion: Our reports demonstrated that DDX41VUS occurs in 1% of patients with myeloid disorders and shares distinct diagnostic features but comparable prognostic features vs. DDX41path, including family history of hematological malignancies. It is possible that many of the cases with 'cytopenias' and DDX41VUS would meet criteria for CCUS if the variant was isolated classified as pathogenic, confirming the importance of extending our understanding of DDX41 variants. Further analysis to characterize the biological impact of DDX41VUS is underway. Figure 1 Figure 1. Disclosures Badar: Pfizer Hematology-Oncology: Membership on an entity's Board of Directors or advisory committees. Al-Kali: Novartis: Research Funding; Astex: Other: Research support to institution. Patnaik: Kura Oncology: Research Funding; Stemline Therapeutics: Membership on an entity's Board of Directors or advisory committees; Stemline Therapeutics: Membership on an entity's Board of Directors or advisory committees. Litzow: Astellas: Research Funding; Omeros: Other: Advisory Board; Jazz: Other: Advisory Board; Pluristem: Research Funding; Amgen: Research Funding; Biosight: Other: Data monitoring committee; Actinium: Research Funding; AbbVie: Research Funding. Foran: boehringer ingelheim: Research Funding; abbvie: Research Funding; takeda: Research Funding; trillium: Research Funding; revolution medicine: Honoraria; bms: Honoraria; servier: Honoraria; novartis: Honoraria; pfizer: Honoraria; aptose: Research Funding; taiho: Honoraria; certara: Honoraria; sanofi aventis: Honoraria; syros: Honoraria; actinium: Research Funding; gamida: Honoraria; OncLive: Honoraria; kura: Research Funding; h3bioscience: Research Funding; aprea: Research Funding; sellas: Research Funding; stemline: Research Funding.

Abstract Background: The DEAD-box helicase 41 (DDX41), an RNA helicase, have been described as a component of the RNA spliceosome (Cheah et al. International Journal of Hematology 2017). Although DDX41 mutations predispose to late-onset higher grade myeloid neoplasms (MN), these patients may have a trend toward favorable prognosis and outcomes. In this work, we describe the clinical characteristics and survival outcomes of isolated and co-mutated DDX41 patients (pts). Methods: We retrospectively analyzed 4,524 consecutive pts who underwent next-generation sequencing (NGS) (OncoHeme 42 genes panel, Mayo Clinic) testing and included 32 pts harboring pathogenic DDX41 mutation and one pt with proven DDX41 germline variant of unknown significance (VUS). Chart review of DDX41-mutated (m) cases between 2009 and 2021 was conducted after IRB approval. We compared overall survival (OS) of unmatched 27 t(8;21)AML and 40 inv(16) AML pts with 10 m DDX41-AML pts. JMP® Pro 14.1.0 Software was used for statistical analysis. Results: DDX41 mutations characteristics: Our cohort included 19 (58%) myelodysplastic syndromes (MDS), 10 (30%) acute myelogenous leukemia (AML), 2 (6%) myeloproliferative neoplasms (MPN), one clonal cytopenia of undetermined significance (CCUS) (3%) and one (3%) germline carrier. Germline testing was carried out in 10 pts, 9 of whom (90%) were confirmed to be germline). The start-loss variant (p.M1I) was the most common mutation type (N=10, 31%). Other types were frameshift (N=9, 28%), missense mutation (N=8, 25%), nonsense (N=3, 9%), and splice site mutation (N=2, 2%). Twenty-one (65.6%) DDX41 mutations clustered in the N-terminus (NT), 7 (22%) in the helicase-C domain (HCD), and 4 (12.5%) in the DEAD-box domain. Compared to NT mutations, patients with HCD mutation had no family history of solid tumors and were more likely to have an accompanying additional DDX41-VUS (0% vs 70%; p=.001) and (N=6, 86% vs. N=2,10%; p=.0001); respectively. I solated vs. co-mutated DDX41: Twenty (60%) pts were isolated-DDX41 and 13 (40%) were co-mutated. The median DDX41-VAF was 48% vs. 45% (p= .2) in the isolated compared to the co-mutated cases, respectively. The median number of co-mutations in the 13 co-mutated cases was 1 (range,1-3) with DNMT3A (38%), ASXL1 (30%), JAK2 (N=3, 23%), and EZH2 (N=2, 15%) were the most common co-mutations detected. Isolated DDX41 had more males (85% vs. 54%, p=.05), the p.M1I variant (47% vs. 8%, p=.02), normal cytogenetics (100% vs. 91%, p= .02), and less family history of solid tumors (77% vs. 33%, p= .02) compared to their co-mutated counterparts. However, there was no difference in OS (p=.99). Comparison of clinical characteristics and hematological features of isolated and co-mutated DDX41 pts are reported in (Table 1). Treatment and survival outcomes in DDX41-MDS/AML : Twenty-three (80%) patients were treated, MDS pts received hypomethylating agents (HMA) (N=10, 71%), HMA plus Venetoclax (HMA+VEN) (N=1, 7%), erythropoiesis-stimulating agents (N=2, 14%) and lenalidomide (N=1 ,7%). AML pts were treated with induction chemotherapy (N=6, 67%) and HMA+VEN (N=3, 33%). Overall response rate of MDS/AML patients was 77% and 100% of AML pts achieved complete remission (CR) when treated with induction chemotherapy or HMA+VEN regimen. There was no significant difference in OS between responders vs. non-responders 2-yr-OS (90% vs. 50%; p=.38) and treated vs. untreated 2-yr-OS (83% vs. 100%; p=.52). Comparing m DDX41-AML vs. core binding factor-AML: After a median follow-up of 33.3 months, all m DDX41-AML patients were alive. There was a significantly better OS in mDDX41-AML patients compared to pts with t(8;21) AML with 2-yr-OS (100% vs. 51%; p=.024) and a trend of better survival when compared to inv(16) AML 2-yr-OS (100% vs. 84%; p=.2). Conclusion We describe the characteristics and outcomes of m DDX41 patients. We demonstrated that isolated and co-mutated m DDX41 patients have different features. Isolated DDX41 patients had male predominance, more p.M1I variant, normal cytogenetics and less family history of solid tumors. In this study we found that m DDX41 AML has high response to treatment and has comparable (if not possibly better) OS compared to other "favorable risk" AML. This study, although limited by the small number of patients, supports the universal testing for DDX41 mutation in adults with MN diagnosis. Figure 1 Figure 1. Disclosures Al-Kali: Astex: Other: Research support to institution; Novartis: Research Funding. Foran: abbvie: Research Funding; OncLive: Honoraria; boehringer ingelheim: Research Funding; trillium: Research Funding; pfizer: Honoraria; takeda: Research Funding; revolution medicine: Honoraria; bms: Honoraria; gamida: Honoraria; actinium: Research Funding; aptose: Research Funding; novartis: Honoraria; servier: Honoraria; taiho: Honoraria; syros: Honoraria; sanofi aventis: Honoraria; certara: Honoraria; kura: Research Funding; h3bioscience: Research Funding; aprea: Research Funding; sellas: Research Funding; stemline: Research Funding. Badar: Pfizer Hematology-Oncology: Membership on an entity's Board of Directors or advisory committees. Salama: Mayo Clinic: Current Employment, Other: Mayo Clinic had the contractual work for the central pathology review for this study and I was one of the reviewing pathologists; Constellation Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees. Litzow: Astellas: Research Funding; Biosight: Other: Data monitoring committee; Amgen: Research Funding; AbbVie: Research Funding; Actinium: Research Funding; Pluristem: Research Funding; Jazz: Other: Advisory Board; Omeros: Other: Advisory Board. Patnaik: Stemline Therapeutics: Membership on an entity's Board of Directors or advisory committees; Kura Oncology: Research Funding; Stemline Therapeutics: Membership on an entity's Board of Directors or advisory committees.