Citations

Abstract Introduction: Therapy-related myeloid neoplasm (t-MN) is defined as the development of a myeloid neoplasm in the context of prior DNA damaging therapies. t-MN is an aggressive disease with no effective therapies. BCL2-inhibitor venetoclax (VEN) represents a novel treatment for acute myeloid leukemia (AML) patients including those with high-risk features. Available VEN studies included only a small portion of t-AML patients, and its efficacy in t-MDS is not known. Our aim was to study the efficacy and outcomes of VEN in t-MN. Methods: Patients diagnosed with t-MN based on the WHO criteria who received VEN were identified. Minimal residual disease (MRD) assessment was performed in a subset of patients by multiparametric flow cytometry or molecular marker as available. Best response to VEN was divided into 3 categories: 1) MRD(-) complete remission (CR); 2) other CR [including complete morphological remission, MRD(+) CR, and CR with incomplete count recovery]; and 3) partial response/progressive disease/stable disease (PR/PD/SD). Progression-free (PFS) and overall survival (OS) were calculated from the time of initiation of VEN therapy using Kaplan-Meier analysis using Wilcoxon test. Logistic regression analysis was performed using Cox Proportional Hazard method. Statistical analysis was performed using JMP (v14.1, SAS Institute) and significance was defined as P<0.05. Results: Of 332 t-MN patients identified (248 at Mayo Clinic, 84 at the Central Adelaide Health Network), 65 (19.6%) received VEN. Clinical and pathological characteristics of patients that received VEN and did not receive VEN (non-VEN) were matched except: a higher proportion of VEN patients had t-AML (49.2% vs. 32.6%, P=0.004), higher peripheral (2% vs. 0%, P=0.02), and bone marrow blasts (18% vs. 8%, P=0.02). VEN patients had a higher proportion of abnormality of chromosome 17, complex karyotype, and monosomal karyotype compared to non-VEN patients. The proportion of patients with pathogenic/likely pathogenic variant (PV) in TP53 or RAS genes was not different. The proportion of patients receiving stem cell transplant for t-MN was not different (Table 1). The indication for VEN was treatment naïve t-MN, relapsed/refractory (R/R) disease, and maintenance in 31 (47.7%), 32 (49.2%), and 2 (3.1%) patients respectively. Prior to VEN, patients received a median of 1 (range 0-4) lines of therapy. The median duration of VEN exposure was 3 cycles (IQR 1-4). VEN was administered with azacitidine, decitabine, low dose cytarabine, intensive chemotherapy, single agent, and >1 agents in 37.9%, 40.9%, 12.1%, 4.5%, 4.5%, and 2.9% respectively. The best and the final responses to VEN are shown in Table 2. Median PFS and OS from initiation of VEN was 5 months (IQR 2-9.5, Fig. A) and 6.5 months (2-14.5, Fig. B) respectively. Female sex (vs. male, χ 2 9.6, P=0.03), VEN as the 1 st line of therapy (vs. other line of therapy, χ 2 8.3, P=0.02), and hypomethylating agent (HMA)-backbone (vs. other, χ 2 12.1, P=0.02) were associated with a significantly higher likelihood of achieving CR. Abnormality of chromosome 7 was associated with a shorter PFS (3.5 vs. 6 months, P=0.03) and OS (4.7 vs. 10.5 months, P=0.02). Using VEN as the 1 st line therapy was associated with an improved PFS (5.5 vs. 2.7 months, P<0.01) and a trend towards improved OS (9.3 vs. 5.1 months, P=0.06). Using HMA (n=51), Ara-C based (n=8), and single agent VEN (n=3) was associated with median PFS of 5.5, 4.2, and 1.5 months (P<0.01) and OS of 9.1, 4, and 1.5 months (P<0.01, Fig. C) respectively. Achieving MRD(-) CR (n=7), other CR (n=17), and PR/PD/SD (n=36) was associated with a median PFS of 7.7, 9.5, and 2 months (P<0.001) and median OS not reached, 12.9, and 2.9 months respectively (P<0.01, Fig. D). Finally, best response rate, PFS, and OS did not differ based on morphological diagnosis [t-MDS vs. t-AML] at diagnosis or bone marrow blast percent [<20% vs. ≥20%] at the start of VEN therapy. On multivariate analysis, only the best response remained an independent predictor of PFS and OS. Conclusion: VEN induced remission, including MRD(-) remission, in a subset of patients. However, progression was noted in 83% patients with continued use, and PFS and OS were overall short. The morphological diagnosis of t-MDS/t-AML or blast percentage at the start of VEN therapy did not impact outcome. Earlier use of VEN, using HMA-based therapies, and achieving deeper responses were associated with improved outcomes. Figure 1 Figure 1. Disclosures Al-Kali: Novartis: Research Funding; Astex: Other: Research support to institution. Patnaik: StemLine: Research Funding; Kura Oncology: Research Funding. Wei: Astra Zeneca: Membership on an entity's Board of Directors or advisory committees, Research Funding; Agios: Membership on an entity's Board of Directors or advisory committees; Genentech: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; Macrogenics: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Celgene/BMS: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Astellas: Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Abbvie: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Tiong: Pfizer: Consultancy; Amgen: Speakers Bureau; Servier: Consultancy, Speakers Bureau. 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. OffLabel Disclosure: venetoclax is not approved in the treatment of myelodysplastic syndrome.

Abstract Background: Pts with HR-MDS unfit for hematopoietic stem cell transplant (HSCT) have poor outcomes and limited survival with single-agent hypomethylating agent (HMA) therapy. Novel treatments that provide durable responses and clinically meaningful survival benefit for pts with HR-MDS are needed. TIM-3 is a promising target in myeloid malignancies as it regulates innate and adaptive immune cells and is expressed on leukemic stem cells (LSCs) and blasts but not normal hematopoietic stem cells. Sabatolimab (MBG453) is a novel immuno-myeloid therapy that binds to TIM-3 on immune cells, facilitating antileukemic immune activation and phagocytic killing of leukemic cells. Sabatolimab also binds to TIM-3 on leukemic cells, potentially impeding self-renewal of LSCs via inhibition of TIM3-galectin-9. In an early phase (ph) trial (NCT03066648) sabatolimab + HMA therapy showed a durable clinical benefit and was well tolerated in pts with HR-MDS (Wei, EHA 2021). Study Design and Methods: The STIMULUS immuno-myeloid clinical trial program is investigating the safety, efficacy, and durability of multiple sabatolimab-based combination therapies in pts with myeloid malignancies. Additional exploration of the mechanism of action of sabatolimab and identification of potential biomarkers predictive of response is planned. This abstract summarizes the design of the 4 ongoing STIMULUS trials in previously untreated adult pts with HR-MDS who are not eligible for intensive chemotherapy (IC) or HSCT. STIMULUS-MDS1 (NCT03946670) is an international, randomized, double-blind, placebo-controlled Ph II trial evaluating sabatolimab + HMA therapy in pts with very-high, high-, or intermediate-risk (vH/H/IR)-MDS which has completed enrollment (N=127). The primary endpoints of STIMULUS-MDS1 are complete response (CR) and progression-free survival (PFS). STIMULUS-MDS2 (NCT04266301) is an ongoing, international, randomized, double-blind, placebo-controlled, Ph III trial of sabatolimab + azacitidine (AZA) in pts with vH/H/IR-MDS or chronic myelomonocytic leukemia-2. Target enrollment is ~500 pts. The primary endpoint in this trial is overall survival (OS). Key secondary endpoints are time to definitive deterioration of fatigue; duration of RBC transfusion-free interval; and improvement of fatigue, physical functioning, and emotional functioning. Other endpoints include CR, marrow CR (mCR), partial remission (PR), PFS, and leukemia-free survival (LFS). STIMULUS-MDS2 is a trial that aims to determine if sabatolimab + HMA has a statistically significant and clinically meaningful benefit in OS and quality of life vs HMA alone. STIMULUS MDS-US (NCT04878432) is a US-based, open-label, single-arm, Ph II trial investigating sabatolimab + HMAs of investigators' choice (AZA intravenous [IV] or subcutaneous, decitabine IV or oral decitabine) in pts with vH/H/IR-MDS. Target enrollment is 90 pts. Primary endpoint is safety, which will be evaluated via incidence and severity of adverse events (AEs) and serious AEs. Secondary endpoints include CR, PFS, LFS, and OS. This trial will provide further understanding of sabatolimab + HMA therapy with additional insight into the safety and efficacy of sabatolimab + oral HMA. STIMULUS-MDS3 (NCT04812548) is an international, open-label, single-arm, Ph II trial that explores triplet therapy of sabatolimab combined with AZA and the BCL-2 inhibitor venetoclax (VEN) in pts with vH/HR-MDS. Part 1 of this trial is a safety run-in comprising 2 safety cohorts with ~6 pts receiving sabatolimab 400 mg + AZA + VEN and ~12 pts receiving sabatolimab 800 mg + AZA + VEN. Primary endpoint of part 1 is safety (dose-limiting toxicities between cycle 1 day 8 and end of cycle 2). If (both 400 and 800 mg) sabatolimab + AZA and VEN are safe, the trial will progress to an expansion cohort (~58 pts) of sabatolimab 800 mg Q4W + AZA + VEN. The primary endpoint is CR. Secondary endpoints include CR + mCR rate, overall response rate (CR + mCR + PR + hematologic improvement), OS, PFS, LFS, and event-free survival. The STIMULUS immuno-myeloid clinical trial program is investigating the efficacy, safety, and improved quality of life of multiple sabatolimab-based combination therapies in pts with myeloid malignancies. The goal of ongoing STIMULUS-MDS trials is to gain insight into the promising durable benefit of sabatolimab combination therapies in pts with HR-MDS. Figure 1 Figure 1. Disclosures Zeidan: Jazz: Consultancy; Jasper: Consultancy; Pfizer: Other: Travel support, Research Funding; AstraZeneca: Consultancy; Janssen: Consultancy; Novartis: Consultancy, Other: Clinical Trial Committees, Travel support, Research Funding; Loxo Oncology: Consultancy, Other: Clinical Trial Committees; Ionis: Consultancy; Kura: Consultancy, Other: Clinical Trial Committees; Incyte: Consultancy, Research Funding; Gilead: Consultancy, Other: Clinical Trial Committees; Genentech: Consultancy; Epizyme: Consultancy; Daiichi Sankyo: Consultancy; Geron: Other: Clinical Trial Committees; BMS: Consultancy, Other: Clinical Trial Committees, Research Funding; Cardiff Oncology: Consultancy, Other: Travel support, Research Funding; Boehringer Ingelheim: Consultancy, Research Funding; BioCryst: Other: Clinical Trial Committees; BeyondSpring: Consultancy; Astex: Research Funding; Astellas: Consultancy; Aprea: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Agios: Consultancy; ADC Therapeutics: Research Funding; Acceleron: Consultancy, Research Funding; AbbVie: Consultancy, Other: Clinical Trial Committees, Research Funding. Al-Kali: Astex: Other: Research support to institution; Novartis: Research Funding. Borate: Takeda: Membership on an entity's Board of Directors or advisory committees; Genentech: Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Jazz Pharma: Research Funding; Blueprint Medicine: Membership on an entity's Board of Directors or advisory committees; Daiichi-Sankyo: Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding; Astellas: Membership on an entity's Board of Directors or advisory committees; incyte: Membership on an entity's Board of Directors or advisory committees, Research Funding; Rampal: Membership on an entity's Board of Directors or advisory committees; Galecto, Inc.: Consultancy; Promedior: Consultancy. Cluzeau: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel, accommodations, expenses, Speakers Bureau; Abbvie: Consultancy, Honoraria, Speakers Bureau; Agios: Honoraria; Amgen: Speakers Bureau; Jazz Pharma: Consultancy, Honoraria; Roche: Consultancy, Honoraria; Astellas: Speakers Bureau; BMS/Celgene: Consultancy, Honoraria, Speakers Bureau; Pfizer: Other: travel, accommodations, expenses; Takeda: Other: travel, accommodations, expenses. DeZern: Taiho: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: 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; Bristol-Myers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees. Esteve: Jazz: Consultancy; Novartis: Consultancy, Research Funding; Astellas: Consultancy; Abbvie: Consultancy; Bristol Myers Squibb/Celgene: Consultancy; Pfizer: Consultancy; Novartis: Research Funding. Giagounidis: Novartis: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees. Platzbecker: Celgene/BMS: Honoraria; Novartis: Honoraria; Janssen: Honoraria; Geron: Honoraria; AbbVie: Honoraria; Takeda: Honoraria. Sallman: Kite: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees; Incyte: Speakers Bureau; Syndax: Membership on an entity's Board of Directors or advisory committees; Intellia: Membership on an entity's Board of Directors or advisory committees; Shattuck Labs: Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy; Aprea: Membership on an entity's Board of Directors or advisory committees, Research Funding; Magenta: Consultancy. Santini: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Menarini: Membership on an entity's Board of Directors or advisory committees; BMS/Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Geron: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Astex: Membership on an entity's Board of Directors or advisory committees. Sanz: Amgen: 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, Speakers Bureau; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, accommodations, and expenses, Research Funding; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Travel, accommodations, and expenses, Speakers Bureau; Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Travel, accommodations, and expenses; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Helsinn Healthcare: Consultancy, Membership on an entity's Board of Directors or advisory committees; Boehringer Ingelheim: Consultancy, Membership on an entity's Board of Directors or advisory committees; Gilead Sciences: Other: Travel, accommodations, and expenses. Sekeres: Novartis: Membership on an entity's Board of Directors or advisory committees; Takeda/Millenium: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees. Wei: Astra Zeneca: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene/BMS: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Agios: Membership on an entity's Board of Directors or advisory committees; Genentech: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Abbvie: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Astellas: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Servier: Membership on an entity's Board of Directors or advisory committees, Research Funding; Macrogenics: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees. Van Hoef: Novartis Pharma: Current Employment. Nourry-Boulot: Novartis: Current Employment. Sadek: Novartis: Current Employment. Bengoudifa: Novartis Pharma AG: Current Employment. Sachs: Novartis Pharma AG: Current Employment. Sabo: Novartis: Current Employment, Current holder of stock options in a privately-held company. OffLabel Disclosure: Sabatolimab is a novel immuno-myeloid therapy targeting TIM-3 and is under investigation for the treatment of patients with myeloid malignancies

Abstract Background/Introduction: Lower-risk (IPSS low risk and Int-1) myelodysplastic syndromes (MDS) are typically treated supportively to address cytopenias. DNA methyltransferase inhibitors (DNMTi) such as azacitidine and decitabine (DEC) are FDA-approved for higher risk MDS patients (pts), and while the DEC USPI includes IPSS Int-1 pts, it is not widely used in this population. Approved intravenous (IV) or subcutaneous (SC) regimens require 5-7 days of treatment every month burdening older cancer pts due to daily travel and treatment time and may increase potential risk from pandemic SARS-CoV-2 infection. Because DNMTis are rapidly degraded by cytidine deaminase (CDA) in the gut and liver, oral availability has only been recently possible. A randomized study with CC-486, an oral formulation of azacitidine, in the Int-1 population showed a median overall survival (mOS) of approximately 17 months for both placebo and treated patients (Garcia-Manero, 2021). Oral DEC 35 mg/cedazuridine 100 mg (ASTX727) or DEC-C, is an oral fixed dose combination (FDC) of DEC and the CDA inhibitor cedazuridine (CED) resulting in equivalent exposure (99%; 90% CI 93% to 106%) to standard IV DEC 20 mg/m 2 for 5 days in an intra-patient randomized cross-over study (Garcia-Manero et al, ASH 2019). Here, we present data on patients with lower risk MDS from that study. Methods: We used a randomized cross over design with pts randomized 1:1 in the first 2 cycles to either Sequence A: (DEC 35 mg/ CED 100 mg in Cycle 1 and IV DEC at 20 mg/m 2 in Cycle 2), or Sequence B (IV DEC in Cycle 1 and oral DEC/CED in Cycle 2). Cycles were repeated every 28 days unless delays were needed, and all patients received oral DEC-C in Cycles 3+ until disease progression or unacceptable toxicity. We conducted an intra-patient comparison of DEC PK (DEC AUC equivalence over 5 days of dosing). Pts were eligible as per the FDA-approved label of IV DEC (MDS pts by FAB classification including CMML, or MDS IPSS Intermediate-1, 2 or high-risk pts). Clinical endpoints were best response as assessed by an independent expert panel according to IWG 2006 response criteria, transfusion independence (TI), overall survival (OS), and safety. Results: Of the 133 pts treated in ASCERTAIN, 69 had a diagnosis of lower-risk MDS (93% Int-1, 7% LR). Median age was 70.0 years (range 45-87), 65% were male, median weight was 84 kg (range 50-127), median baseline hematologic parameters were: hemoglobin 89 g/L (range 69.8-146.5), WBCs 1.50 X 10 9/L (range 0.11-7.1), platelets (plt) 86 x 10 9/L (range 5-703), bone marrow blasts 4% (range 0-18), cytogenetics: 7 (10.1%) poor-risk, 21 (30.4%) intermediate risk, 37 (53.6%) better-risk, 4 (5.7%) missing or not evaluable. 27(39%) of the pts were RBC transfusion dependent (TD) and 6 (9%) plt TD. 17 (25%) had received prior MDS treatment, 3% prior DNMTi. Pts received a median of 9 cycles of therapy (range 1-28). Treatment-emergent adverse events of CTCAE Gr 3 or higher in >10% of pts, independent of relationship to ASTX727, included cytopenias (neutropenia [59%], thrombocytopenia [58%], anemia [48%], leukopenia [26%]), febrile neutropenia (32%), and pneumonia (19%). Sixteen pts (23%) achieved Complete Response (CR), 18 (26%) had marrow CR (mCR), including 9 (13%) with hematologic improvement (HI). Overall Response rate (ORR; CR + PR+ mCR + HI) was 57%. Of those RBC or plt TD at baseline, 13 (48%) became RBC TI and 4 (67%) became plt TI. With approximately 32 months of median follow up, neither median leukemia-free survival (mLFS) nor mOS had been reached (Figure 1). Twelve pts (17%) went on to allogeneic stem cell transplant. Conclusions: Oral decitabine/cedazuridine given as a FDC in MDS pts produced equivalent PK exposure to 20 mg/m 2 IV DEC; in lower risk MDS pts with treatment indicated, the agent was generally well-tolerated with prolonged treatment and could result in mLFS and mOS which exceeds 32 months. This FDC and other dosing regimens of oral DEC-C should be further studied in this patient population. References: Garcia-Manero, et al, ASH 2019 Savona, et al, Int. MDS Symp. 2021 Garcia-Manero, et al, Phase III, Randomized, Placebo-Controlled Trial of CC-486 (Oral Azacitidine) in Patients with Lower-Risk Myelodysplastic Syndromes. J.Clin.Onc. 2021 39:13, 1426-1436 Figure 1 Figure 1. Disclosures McCloskey: Pfizer: Consultancy; Jazz: Consultancy, Speakers Bureau; COTA: Other: Equity Ownership; Incyte: Speakers Bureau; Takeda: Consultancy, Speakers Bureau; Novartis: Consultancy; BMS: Honoraria, Speakers Bureau; Amgen: Speakers Bureau. Griffiths: Alexion Pharmaceuticals: Consultancy, Research Funding; Abbvie: Consultancy, Honoraria; Taiho Oncology: Consultancy, Honoraria; Genentech: Research Funding; Novartis: Honoraria; Takeda Oncology: Consultancy, Honoraria; Astex Pharmaceuticals: Honoraria, Research Funding; Celgene/Bristol-Myers Squibb: Consultancy, Honoraria, Research Funding; Apellis Pharmaceuticals: Research Funding; Boston Biomedical: Consultancy. Yee: Paladin: Membership on an entity's Board of Directors or advisory committees; TaiHo: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech: Research Funding; Geron: Research Funding; Janssen: Research Funding; Jazz: Research Funding; MedImmune: Research Funding; Onconova: Research Funding; Tolero: Research Funding; AbbVie: Honoraria; Bristol-Myers Squibb/Celgene: Membership on an entity's Board of Directors or advisory committees; Otsuka: Membership on an entity's Board of Directors or advisory committees; Shattuck Labs: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; F. Hoffmann La Roche: Membership on an entity's Board of Directors or advisory committees, Research Funding; Forma Therapeutics: Research Funding; Astex: Membership on an entity's Board of Directors or advisory committees, Research Funding. Zeidan: Novartis: Consultancy, Other: Clinical Trial Committees, Travel support, Research Funding; Genentech: Consultancy; Ionis: Consultancy; Astellas: Consultancy; Epizyme: Consultancy; AbbVie: Consultancy, Other: Clinical Trial Committees, Research Funding; Jasper: Consultancy; Cardiff Oncology: Consultancy, Other: Travel support, Research Funding; BeyondSpring: Consultancy; Loxo Oncology: Consultancy, Other: Clinical Trial Committees; Janssen: Consultancy; Acceleron: Consultancy, Research Funding; AstraZeneca: Consultancy; Kura: Consultancy, Other: Clinical Trial Committees; Gilead: Consultancy, Other: Clinical Trial Committees; Agios: Consultancy; Daiichi Sankyo: Consultancy; Boehringer Ingelheim: Consultancy, Research Funding; Geron: Other: Clinical Trial Committees; BMS: Consultancy, Other: Clinical Trial Committees, Research Funding; BioCryst: Other: Clinical Trial Committees; Pfizer: Other: Travel support, Research Funding; Aprea: Consultancy, Research Funding; ADC Therapeutics: Research Funding; Jazz: Consultancy; Incyte: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Astex: Research Funding. Al-Kali: Astex: Other: Research support to institution; Novartis: Research Funding. Patel: Celgene-BMS: Membership on an entity's Board of Directors or advisory committees; PVI: Honoraria; Agios: Membership on an entity's Board of Directors or advisory committees. Sabloff: Pfizer: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; ROCHE: Membership on an entity's Board of Directors or advisory committees; TaiHo: Membership on an entity's Board of Directors or advisory committees; Jaxx: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees. Dao: Astex Pharmaceuticals, Inc.: Current Employment. Fazal: Taiho Pharmaceuticals: Consultancy, Honoraria, Speakers Bureau; Stemline Therapeutics: Consultancy, Honoraria, Speakers Bureau; Sanofi Genzyme: Consultancy, Honoraria, Speakers Bureau; Novartis: Consultancy, Honoraria, Speakers Bureau; Karyopharm Pharmaceuticals: Consultancy, Honoraria, Speakers Bureau; Jazz Pharmaceuticals: Consultancy, Honoraria, Speakers Bureau; Janssen Oncology: Consultancy, Honoraria, Speakers Bureau; Incyte: Consultancy, Honoraria, Speakers Bureau; Glaxo Smith Kline: Consultancy, Honoraria, Speakers Bureau; Gilead Sciences: Consultancy, Honoraria, Speakers Bureau; Bristol Myers Squibb: Consultancy, Honoraria, Speakers Bureau; AMGEN: Consultancy, Honoraria, Speakers Bureau; Agios: Consultancy, Honoraria, Speakers Bureau; Takeda: Consultancy, Honoraria, Speakers Bureau. Odenike: AbbVie, Celgene, Impact Biomedicines, Novartis, Taiho Oncology, Takeda: Consultancy; Celgene, Incyte, AstraZeneca, Astex, NS Pharma, AbbVie, Gilead, Janssen, Oncotherapy, Agios, CTI/Baxalta, Aprea: Research Funding. Kantarjian: AbbVie: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Ascentage: Research Funding; Pfizer: Honoraria, Research Funding; BMS: Research Funding; Daiichi-Sankyo: Research Funding; Amgen: Honoraria, Research Funding; Ipsen Pharmaceuticals: Honoraria; Jazz: Research Funding; Astellas Health: Honoraria; Immunogen: Research Funding; Astra Zeneca: Honoraria; Aptitude Health: Honoraria; KAHR Medical Ltd: Honoraria; NOVA Research: Honoraria; Precision Biosciences: Honoraria; Taiho Pharmaceutical Canada: Honoraria. DeZern: Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees; Taiho: 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; Bristol-Myers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees. Roboz: Novartis: Consultancy; Mesoblast: Consultancy; Jasper Therapeutics: Consultancy; Jazz: Consultancy; MEI Pharma - IDMC Chair: Consultancy; Daiichi Sankyo: Consultancy; Otsuka: Consultancy; Bristol Myers Squibb: Consultancy; Blueprint Medicines: Consultancy; Bayer: Consultancy; AstraZeneca: Consultancy; Astellas: Consultancy; Astex: Consultancy; Amgen: Consultancy; Agios: Consultancy; Actinium: Consultancy; AbbVie: Consultancy; Janssen: Research Funding; Celgene: Consultancy; Glaxo SmithKline: Consultancy; Helsinn: Consultancy; Janssen: Consultancy; Pfizer: Consultancy; Roche/Genentech: Consultancy. Busque: Novartis: Consultancy. Leber: Astellas: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Otsuka: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; TaiHo: Honoraria, Membership on an entity's Board of Directors or advisory committees; AMGEN: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Abbvie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Jazz: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Hao: Astex Pharmaceuticals, Inc.: Current Employment. Keer: Astex Pharmaceuticals, Inc.: Current Employment. Azab: Astex Pharmaceuticals, Inc.: Membership on an entity's Board of Directors or advisory committees. Savona: Geron: Consultancy, Membership on an entity's Board of Directors or advisory committees; Karyopharm: Consultancy, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; CTI: Consultancy, Membership on an entity's Board of Directors or advisory committees; BMS-Celgene: 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; Ryvu: Consultancy, Membership on an entity's Board of Directors or advisory committees; Sierra Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Taiho: Consultancy, Membership on an entity's Board of Directors or advisory committees; TG Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; ALX Oncology: Research Funding; Astex: Research Funding; Incyte: Research Funding.

Summary We describe our single institution experience with cladribine therapy in 42 patients with systemic mastocytosis (SM): 22 advanced (adv‐SM; median age 65 years, 68% males) and 20 indolent/smouldering SM (ISM/SSM; median age 56 years, 45% males); subcategories included eight aggressive, 13 associated with another haematological neoplasm, one mast cell leukaemia, 17 ISM and three SSM. Overall/major response rates were 77%/45% for adv‐SM and 70%/60% for ISM/SSM, and median (range) duration of response 10 (4–75) and 46 (4–140) months respectively. A >50% reduction in bone marrow mast cell burden and serum tryptase level was documented in 63% and 67% of patients with adv‐SM and 50% and 46% with ISM/SSM respectively. The presence of KIT proto‐oncogene, receptor tyrosine kinase ( KIT ) D816V predicted response in adv‐SM: 17 (90%) of 19 with and none of three without the mutation responded ( P < 0·01). Treatment‐emergent adverse events were mostly limited to transient cytopenias: Grade 3/4 neutropenia, thrombocytopenia, or lymphopenia occurred in 27%, 27% and 27% of patients with adv‐SM, and 5%, 5% and 30% with ISM/SSM respectively. The present study provides practical information that might be considered when making treatment choices between cladribine and newer KIT‐targeted therapies and identifies the absence of KIT D816V as a potential marker of cladribine resistance in advanced SM; the latter observation needs confirmation in a larger study.

Abstract DDX41 mutations (germline and somatic) are associated with late onset myelodysplastic syndromes/acute myeloid leukemia (MDS/AML). Myeloid neoplasms (MN) with germline predisposition was identified as a distinct category in the 2016 WHO classification revision, including MN with germline DDX41 mutation. We retrospectively analyzed the molecular findings and clinical characteristics of thirty-three DDX41-mutated (mDDX41) patients at our institution. We identified 14 distinct pathogenic DDX41 variants in 32 patients and 8 DDX41 variants of unknown significance (VUS) in 9 patients. Five (16%) patients had a second DDX41 somatic mutation p.R525H and 13 (40%) had at least one additional oncogenic co-mutation in other genes. The median age at the time of diagnosis was 66 years, with male predominance (72%) and the majority of patients had normal cytogenetics (91%). Two-year overall survival (OS) was 86% and 6 (21%) MDS/AML patients with relatively preserved hematopoietic function were observed without further intervention. In comparison to AML patients with prognostically more favorable subtypes [t(8;21), n=27 and inv(16), n=40], mDDX41 patients in our cohort showed similarly favorable OS. Our study highlights that mDDX41-MN patients often have an indolent course and mDDX41-AML has comparable OS to favorable-risk AML.

AbstractGermline predisposition syndromes (GPS) result from constitutional aberrations in tumor suppressive and homeostatic genes, increasing risk for neoplasia in affected kindred. In this study, we present clinical and genomic data on 144 Mayo Clinic patients with GPS; 59 evaluated prospectively using an algorithm‐based diagnostic approach in the setting of a dedicated GPS/ inherited bone marrow failure syndrome (IBMFS) clinic. Seventy‐two (50%) patients had IBMFS (telomere biology disorders‐32,Fanconi anemia‐18, Diamond Blackfan Anemia – 11, congenital neutropenia–5, Schwachman‐Diamond Syndrome‐5 and Bloom Syndrome‐1), 27 (19%) had GPS with antecedent thrombocytopenia (RUNX1‐FPD‐15, ANKRD26‐6, ETV6‐2, GATA1‐1, MPL‐3), 28 (19%) had GPS without antecedent thrombocytopenia (GATA2 haploinsufficiency‐16, DDX41‐10, CBL‐1 and CEBPA‐1) and 17 (12%) had general cancer predisposition syndromes (ataxia telangiectasia‐7, heterozygous ATM variants‐3, CHEK2‐2, TP53‐2, CDK2NA‐1, NF1‐1 and Nijmegen Breakage Syndrome‐1). Homozygous and heterozygous ATM pathogenic variants were exclusively associated with lymphoproliferative disorders (LPD), while DDX41 GPS was associated with LPD and myeloid neoplasms. The use of somatic NGS‐testing identified clonal evolution in GPS patients, with ASXL1, RAS pathway genes, SRSF2 and TET2 being most frequently mutated. Fifty‐two (91%) of 59 prospectively identified GPS patients had a change in their management approach, including additional GPS‐related screening in 42 (71%), referral for allogenic HSCT workup and screening of related donors in 16 (27%), medication initiation and selection of specific conditioning regimens in 14 (24%), and genetic counseling with specific intent of fertility preservation and preconceptual counseling in 10 (17%) patients; highlighting the importance of dedicated GPS screening, detection and management programs for patients with hematological neoplasms.