Citations

AbstractPregnancy in the context of myeloproliferative neoplasms (MPN) poses unique fetal and maternal challenges. Current literature in this regard mostly involves essential thrombocythemia (ET) and less so polycythemia vera (PV) or myelofibrosis. In ET, live birth rate is estimated at 70% with first trimester fetal loss (˜ 30%) as the major complication. Risk of pregnancy‐associated complications is higher in PV, thus mandating a more aggressive treatment approach. Herein, we appraise the relevant literature, share our own experience and propose management recommendations. Aspirin therapy may offer protection against fetal loss; however the additive benefit of systemic anticoagulation or cytoreductive therapy, in the absence of high risk disease, is unclear. We recommend cytoreductive therapy in the form of interferon alpha in all high risk and select low‐risk ET and PV patients with history of recurrent fetal loss, prominent splenomegaly or suboptimal hematocrit control with phlebotomy. In addition, all women with PV should maintain strict hematocrit control <45% with the aid of phlebotomy. Systemic anticoagulation with low molecular weight heparin is advised in patients with history of venous thrombosis. Further clarification awaits prospective clinical trials that implement risk adapted therapeutic interventions.

Key Points Systemic immune microenvironment signatures in CMML indicate an altered T- and natural killer cell balance. CMML bone marrow dendritic cell aggregates associate with disease progression and systemic regulatory T-cell phenotypic switch.

Introduction: Mutations in the gene isocitrate dehydrogenase 2 (IDH2) occur in ~12-15% of patients with acute myeloid leukemia (AML). Enasidenib, an oral small molecule selective targeted inhibitor of IDH2 enzymes, was approved forIDH2mutated relapsed/refractory AML (RR-AML) in 2017 (Stein et. al., 2017). There is limited data regarding its efficacy and toxicity outside the context of clinical trials. Using Mayo Clinic's cohort of AML patients, we provide a real-world look at outcomes forIDH2mutated RR-AML patients treated with enasidenib. Methods: A total of 13 patients treated with enasidenib for RR-AML were identified, all of which experienced at least one relapse following induction chemotherapy. Response assessment was based on European Leukemia Net (ELN) 2017 response criteria.Complete blood counts including blast percentage and transfusion dependency were obtained at AML diagnosis, initiation of enasidenib, 2 months and 6 months following initiation of therapy. Transfusion dependency was defined by the need for either a red cell or platelet transfusion within 4 weeks of the designated time frame. We compared the clinical characteristics of patients who achieved complete response (CR) (n=4) to those not achieving CR (n=9), using the Mann-Whitney U test for numerical variables and the Fischer's Exact test for quantitative data. Results: The median age at diagnosis of our 13 patients was 68 years (range 60-82), with a male predilection (n=11) (Table 1). Cytogenetic and molecular genetic findings are provided in Table 2. Complete response (CR) was achieved in 4 (30.7%) patients by cycle 2 and 2 of those patients (50%) proceeded to an allogeneic hematopoietic stem cell transplant (AHSCT). The median time from diagnosis to initiation of treatment for patients in CR was 3.5 months (range 1-7), and for patients not achieving CR was 13 months (range 6-53; p=0.048), with median time of follow up after treatment initiation of 23.5 months (range, 5-36) and 7 months (range, 1-14), respectively. Among 8 patients who were transfusion dependent at baseline, all the CR patients (2/2) achieved red blood cell and platelet transfusion independence 6 months after treatment, instead only (3/6) 50% of those not in CR achieved transfusion independence (p=0.028). An initial trajectory of improvement in counts is noted from the time of diagnosis to the 2 month mark post treatment with 75% of the responder cohort showing improvement in counts which was durable through the 6 month mark, whereas 55% of those that did not respond had worsening counts at month 2 and died prior to 6 month follow up. At the time of data cut-off, the median duration of CR was 14 months (range, 2-33), with 3 of 4 (75%) of responders maintaining CR. Figure 1 details overall responses and outcomes in all 13 patients. None of the patients in our study experienced differentiation syndrome. Five patients were hospitalized in the course of treatment for infectious complications. Two patients were noted to have hyperbilirubinemia however there was no clear indication that this was secondary to enasidenib Median overall survival for all 13 patients was 21 months (range, 6-53 months) with leukemia free survival of 7 months (range, 5-19 months). Furthermore, median overall survival for patients in CR was 27 months (range, 6-42), and those not in CR was 16 months (range, 6-53) (p=0.20). In addition, we observed that 75% of patients who attained CR are alive compared to 11.1% of those not in CR (p = 0.052). Conclusion: We demonstrate a superior CR rate of 30.7% with enasidenib amongstIDH2mutated RR-AML patients compared with clinical trial data showing CR rate of 19.6% (Stein et. al., 2019) despite our patients being heavily pre-treated with median number of two prior therapies (range; 1-5) including prior AHSCT in 2 patients. Moreover, a subset of patients (2 of 4 in CR) were able to undergo ASCHT. Finally, the achievement of CR at 2 months after initiation of therapy serves as an appropriate time point for response assessment. Disclosures No relevant conflicts of interest to declare.

Introduction Clonal cytopenias of undetermined significance (CCUS) is defined by the presence of somatic driver mutations/copy number variations in hematopoietic cells in patients with low blood counts, in the absence of morphological evidence for myeloid neoplasms. Patients with CCUS are often symptomatic and can be transfusion dependent (TD), with high rates of progression to myeloid neoplasms, especially myelodysplastic syndromes (MDS). In addition, similar to MDS, there are reports of CCUS patients responding to hypomethylating agents. Due to the lack of a formal diagnosis/morphological dysplasia, CCUS patients are often denied therapies or clinical trial enrollment. We carried out this study to validate our hypothesis that CCUS shares similar clinical and survival characteristics with lower risk MDS (LR-MDS). Methods CCUS patients were prospectively identified from the clonal hematopoiesis clinic, whereas LR-MDS patients were retrospectively identified from our institutional database. LR-MDS was defined as very low, low and intermediate risk MDS based on the R-IPSS categorization. Baseline demographics, blood counts, bone marrow (BM) morphology, cytogenetics, and NGS results were abstracted. Transfusion dependency was defined as requiring at least one unit of red cell or platelets every 4 weeks. The Mann-Whitney-U and Fischer's exact test were used to compare quantitative and qualitative data in subgroups. Kaplan-Meier overall survival (OS) estimates were used for survival analysis and compared using the log-rank test. Results 186 patients were included in the study; 74 (40%) with CCUS and 112 (60%) with LR-MDS, median age 66 years, with 63% being male (Table 1). In the CCUS group, 93% had one or more mutations (67% &gt;1 mutation) detected by NGS, while 7% had clonal cytogenetic abnormalities. Common mutations in CCUS included TET2 (30%), SRSF2 (20%), DNMT3A (13%) and ASXL1 (11%); with 28% of patients being red cell TD and 15% being platelet TD. On application of the R-IPSS stratification, 40%, 45%, 12% and 3% were in the very low, low, intermediate and high risk categories, respectively. LR-MDS subtypes included MDS-RS (50%), MDS-MLD (21%), MDS-EB (10%), MDS del5q (7%), and MDS-U (12%). SF3B1 mutations were seen in 67% (95% of MDS-RS), while TET2 and DNMT3A mutations were seen in 29% and 21%, respectively. 60% of LR-MDS patients had &gt;1 mutation. 44% were red cell TD, while 10% were platelet TD. In comparison to patients with CCUS, LR-MDS patients were more likely to have higher white blood cell counts (p=0.002), higher neutrophil counts (p=0.009), higher platelet counts (p&lt;0.001), be red cell TD (p=0.031), have BM ring sideroblasts (p&lt;0.001), have higher BM blast% (p=0.004) and carry SF3B1 mutations (p&lt;0.001); whereas CCUS patients were more likely to have higher monocyte counts (p=0.009) and more likely to carry IDH1 (p=0.005), ZRSR2 (p=0.005) and ATM (p=0.012) mutations. Importantly there were no differences with regards to R-IPSS cytogenetic risk groups, R-IPSS prognostic categories, platelet TD, and mutations involving TET2, DNMT3A, SRSF2 and ASXL1 and TP53. Notably signal pathway mutations and mutations involving tumor suppressor genes were infrequent (&lt;5%) in both groups. The LR-MDS patients had a longer median follow up (53 vs 15 months) and at last follow up 72 (64%) and 11 (15%) deaths had been documented in the LR-MDS and CCUS groups respectively. 13 (18%) CCUS patients progressed to MDS (10) and AML (3) over a median of 15 months, while 9 (8%) LR-MDS patients progressed to higher grade MDS (1) and AML (8), respectively (median follow up 53 months). There was no difference in the median survival between CCUS (median OS not reached) versus LR-MDS (median OS 8.3 years) (p=0.372, Figure 1). Conclusion In spite of subtle phenotypic/molecular differences between LR-MDS and CCUS, both entities had similar prognostication, distribution of high risk mutations and survival outcomes. Within a short follow-up, 18% of CCUS patients progressed to MDS/AML, indicating that regardless of the absence of dysplasia these entities are a continuum of myeloid neoplasms. In order to improve access to treatments and clinical trial opportunities, we recommend that close consideration be given to consider CCUS as a MDS subtype. Disclosures Shah: Dren Bio: Consultancy.

Background Clonal cytopenia of undetermined significance (CCUS) is a newly described entity with a high probability to progress into myeloid disorders upon follow-up (Malcovati et al, Blood 2017). Little data is known on how to effectively treat patients with CCUS. We hereby describe a single institution experience in managing symptomatic CCUS patients. Methods Patients who had CCUS and underwent active treatment were identified after receiving IRB approval. CCUS diagnosis was rendered if patients had non-diagnostic bone marrow biopsy evaluation combined with evidence of pathogenic myeloid somatic mutation using our institution next generation sequencing (NGS) panel (OncoHeme, Mayo Clinic). "Symptomatic patients" is determined by patients who need therapy beyond blood transfusion. Treatment type is based on physicians' choice. Clinical and lab results were collected. Response and progression were graded based on the MDS IWG 2006 criteria. The date of treatment initiation was used for overall survival (OS) and progression (either to myeloid neoplasm or worsening cytopenias) free survival (PFS) calculation. Stata 14.1(StatCorp) was used for data analysis. Results 1) Cohort characteristics: Between 2015 and 2020, 24 patients met inclusion criteria with median age of 72 years (range: 24-87). Twenty (83%) were men. 15 (63%) were white, 1 (4%) African American, 1 (4%) Native American and 7 unknown (33%). Eighty percent had ECOG PS≤1. Four (17%) patients had prior other hematology disorders and 3 (13%) had solid tumor. Two (8%) patients had previous radiation therapy, 2 (8%) received chemotherapy and 1 (4%) received allogeneic stem cell transplantation. At the time of treatment, the median of hemoglobin was 8.9 (range 6.8-13.7) g/dL, white blood cell 2.9 (range 1.4-12.3) *109/L, and platelet 76 (range 8-407) *109/L. Red blood cell (RBC) and platelet transfusion dependency rate were 54% and 29%, respectively. We identified 23 different mutations. Most common mutations occurred in SRSF2 (N=5, 21%), TET2 (N=5, 21%), U2AF1 (N=5, 21%), and TP53 (N=4, 17%). Ten (42%) patients had 1 mutation, and 14 (58%) had ≥2 mutations. Treatment included hypomethylating agents (HMA) (N=10, 42%), growth factors (N=11, 46%), steroid (N=4, 17%), testosterone (N=2, 8%), cyclosporine (N=2, 8%), rituximab (N=1, 4%), immunoglobulin (N=1, 4%), vitamin B12 and iron (N=1, 4%). Seven (29%) patients received ≥2 treatments. Median follow up duration was 17.5 months (range 8.9-26.1). Median time from the diagnosis to treatment was 2.1 months (range 0-26.8). 2) Molecular correlation with response The overall response rate (RR) was 50% (hematological or symptomatic improvement). Most responders (67%) were treated with HMA (p=0.013). HMA treatment effect was not significantly associated with DNA methylation genes (DNMT3A, IDH1, IDH2 and TET2, all p&gt;0.05). The RR was 100% for the three patients with IDH1 mutation (treated with HMA, steroid and erythropoietin stimulating agent (ESA), respectively). The RR was 100% for the 3 patients with ZRSR2 mutation (2 HMA, 1 testosterone). The RR was 0% for 3 patients with SF3B1 mutation (1 testosterone and ESA, 1 vitamin B12 and iron, and 1 HMA). The number of mutations had no impact on RR (p=0.41). Table demonstrates the RR for each treatment. 3) Survival and progression outcome At the last day of follow up, RBC and platelet transfusion dependency rate were 38% and 25%, respectively. The median PFS was 16.9 months (95% CI: 7.5-65.3). Six patients (25%) progressed to myeloid malignancy with 4 myelodysplastic syndrome (MDS) and 2 acute myeloid leukemia (AML). Five patients progressed with worsening cytopenias. Among the 4 MDS patients, they had SF3B1, TET2, and ASXL1 mutations at the diagnosis of CCUS. Within the 2 AML pts, 1 had RUNX1 mutation, 1 had BCOR, DNMT3A, PHF6, RUNX1, SF3B1, STAG2, and TET2 mutations at the diagnosis of CCUS. The median OS was not reached with an estimated 2 year OS 77%. Three (13%) patients progressed with cytopenia and died. Their NGS at CCUS diagnosis showed ASXL1, TP53 and U2AF1 mutations, respectively. Conclusion Patients with CCUS responded to available treatments used for myeloid diseases. HMA were effective in this cohort. Mutation profile may have an impact on treatment response. Studies of larger cohorts are needed to validate our findings. Additionally, development of response and progression criteria would be helpful for such patients for reporting treatment outcomes. Disclosures Shah: Dren Bio: Consultancy.

Introduction: Myeloproliferative neoplasms (MPN), including primary myelofibrosis (PMF), essential thrombocythemia (ET) and polycythemia vera (PV), have a propensity to evolve into blast phase myeloproliferative neoplasm (BP-MPN) with a 20-year incidence rate of 9.3 %, 3.9% and 2.6%, respectively. (Szuber et al., 2019)Treatment options for BP-MPN are limited and the prognosis of these patients is dismal with a median survival of only 3.6 months and 5-year survival rate of &lt;5%.(Tefferi et al., 2018) Considering the recent reported data on the efficacy of venetoclax when combined with hypomethylating agents (HMA) in acute myeloid leukemia (AML) in both relapsed/refractory and newly diagnosed unfit patients, we have extended such combination therapy for patients with BP-MPN. Methods: We retrospectively analyzed 14 consecutive BP-MPN patients who received venetoclax plus HMA therapy between August 2018 and June 2020. We collected data regarding clinical characteristics of chronic phase MPN and BP-MPN, cytogenetic and leukemia mutation profile, efficacy and outcome. Oral venetoclax was administered in combination with azacitidine 75 mg/m2 days 1-7 (5 patients) or decitabine 20 mg/m2 days 1-5 (9 patients). Venetoclax dose was adjusted based on drug interactions particularly with azole antifungal prophylaxis. Diagnostic, risk and response assignments were according to the 2017 European LeukemiaNet (ELN) criteria.(Döhner et al., 2017) Minimal residual disease (MRD) assessment by flow cytometry, karyotype or next-generation sequencing (NGS) was performed in a subset of patients. Results: Patient characteristics at time of leukemic transformation, treatment details, response rates and overall outcome are shown in Table 1. Median age of patients was 67 years (range 48-81) with poor-risk cytogenetics in 69% of patients. JAK2 was mutated in 10 patients (71%) and CALR in 2 (14%); other mutations included TP53 in 5 patients (36%), TET2 in 4 (29%), KRAS in 3 (21%), IDH1/2 in 3 (21%), ASXL1 in 2 (14%) and U2AF1 in 2 (14%). Eight patients (57%) received venetoclax and HMA combination therapy upfront for their BP-MPN, 2 patients (14%) had failed HMA therapy previously and one patient had prior allogeneic hematopoietic stem cell transplant (AHSCT). Two patients (14%) presented with myeloid sarcoma; one of these two patients documented partial resolution of the extramedullary tumor by imaging studies, after treatment with venetoclax plus HMA. Among the remaining 12 patients, overall response rate (ORR) was 42% (n=5) and included complete remission (CR) in 3 patients (25%) and partial remission (PR) in another 2 (17%). The best response to therapy was seen after a median of 1 month (range, 1-2). Among 3 CR responders, 2 (66.6%) had minimal residual disease negative by NGS and not evidence of preceding MPN, then they successfully transitioned to AHSCT, while the third CR patient at the time of best response showed persistence of the TP53 mutation. Additionally, one PR patient subsequently relapsed and received salvage chemotherapy followed by AHSCT. (Table 2) Although data is limited by the small cohort and short follow up when the outcome of patients treated with venetoclax in combination with HMA were compared to Mayo Clinic's historical control of patients with BP-MPN treated with HMA alone (n=26) or intensive chemotherapy (n=69), there was higher CR rate in patients treated with venetoclax and HMA (25%) compared to those receiving HMA alone (4%; p=0.048) but not to those receiving intensive chemotherapy (35%; p&lt;0.0001). Moreover, the intensive chemotherapy cohort showed 24% of CR with incomplete hematologic recovery (CRi) not seen in patients receiving HMA alone or HMA with venetoclax (Figure1). Conclusions: The relatively high rate of complete response observed in our patients with BP-MPN were similar to those reported in a pivotal study of elderly unfit AML patients treated upfront with venetoclax + HMA with overall response rates of 68%.(DiNardo et al., 2019) Furthermore, responders included patients with adverse molecular risk factors who usually respond poorly to conventional chemotherapy (i.e. TP53 mutated patients). Our observations provide preliminary evidence for the potential efficacy of venetoclax and HMA combination therapy in BP-MPN with the goal of achieving CR/CRi followed by consolidative AHSCT wherever possible to provide durable remission and meaningful survival benefit. Disclosures Foran: Agios: Honoraria, Research Funding; Trillium: Research Funding; Takeda: Research Funding; Kura Oncology: Research Funding; Aptose: Research Funding; Aprea: Research Funding; Actinium: Research Funding; Boehringer Ingelheim: Research Funding; Abbvie: Research Funding; BMS: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Revolution Medicine: Consultancy; Xencor: Research Funding; H3Biosciences: Research Funding.

Introduction Germline predisposition syndromes (GPS) are inherited disorders associated with germinal aberrations that increase the risk of malignancies. While aberrations in certain genes increase the risk for all types of malignancies (Tp53, ATM, CDKN2A, CHEK2), there is a growing list of genes associated specifically with hematological malignancies (GATA2, RUNX1, DDX41, ETV6, ANKRD26). At our institution, we have established a hematology GPS clinic to diagnose and manage GPS and with this report, detail our experience with 130 patients. Methods GPS were investigated in pediatric and adult patients with one or more first degree relatives with hematological/visceral malignancies or in those with antecedent thrombocytopenia (ANKRD26, RUNX1, ETV6), or with specific syndromic features (short telomere syndromes/STS, GATA2 haploinsufficiency, Fanconi anemia/FA, Shwachman-Diamond syndrome/SDS). Depending on the phenotype, specific functional assays such as flow-FISH for telomere length assessment and chromosomal breakage assays were ordered. After informed consent and genetic counselling, germline testing was carried out on peripheral blood mononuclear cell, skin fibroblast, or hair follicle-derived DNA. A custom-designed marrow failure NGS panel (200 genes) was used in most cases and interrogation of variants, in silico studies, and functional assays were carried out as previously described (Mangaonkar et al MC Proc 2019). Copy number variations were identified by aCGH. At the time of progression/worsening cytopenias, bone marrow/lymph node biopsies and NGS (next generation sequencing) were carried out where indicated. Results 130 patients with germline predisposition have been identified to date. The spectrum of disorders seen include STS 29 (22%), FA 17 (13%), GATA2 16 (12%), Diamond Blackfan anemia/DBA 13 (10%), RUNX1-FPD 12 (9%), ATM deletions/mutations 11 (8%), ANKRD26 6 (5%), SDS 5 (4%), DDX41 4 (3%), MPL 3 (2%), CHEK2, MECOM, Tp53 mutations 2 (2%) each, and CBL, CEPBA, ELANE, NF1, CDKN2A, CSF3R, ETV6, and GATA1 mutations, 1 (1%) each. Evidence for clonal evolution (CCUS) and hematological malignancies were seen in 51 (39%) patients, involving all the aforementioned genes/syndromes with the exception of DBA, CBL, ETV6, MPL, CSF3R, and GATA1. Seven (64%) of 11 patients with germline ATM deletions/mutations developed lymphoid malignancies; homozygous ATM (Follicular NHL-1, Burkitt lymphoma-1, T-ALL-1, T-LPD-1) and heterozygous ATM (T-PLL-1, DLBCL-1, CLL-1). Clonal evolution occurred in 11 (69%) of 16 GATA2 haploinsufficient patients (CCUS-2, MDS-3, CMML-1, AML-5) and in 7 (58%) of 12 RUNX1-FPD patients (CCUS-1, MDS-1, MDS/MPN-3, AML-2). Five of 29 (17%) STS patients had clonal progression (CCUS-2, MDS-2, AML-1), and 5 (29%) of 17 FA patients progressed to MDS-2 or AML-3. JMML was seen in one patient with a germline NF1 mutation, while 1 (20%) of 5 SDS patients progressed to AML. NGS data at progression was available in 24 (55%) of 44 myeloid/CCUS progressions, with somatic truncating ASXL1 mutations being most frequent (29%), followed by RAS pathway mutations (15%). AML/MDS progressions in STS, FA, and SDS were universally associated with complex/monosomal karyotypes, translating to refractory disease. Seventeen (39%) of 44 patients with myeloid predisposition underwent allogenic HCT (GATA2-7, FA-3, RUNX1-FPD-3, STS-2, NF1-1, Tp53-1), with 10 (59%) being alive at last follow up (Table 1). Conclusion We demonstrate the spectrum of germline aberrations associated with predisposition to hematological malignancies and outline the phenotypic heterogeneity of clonal transformation. The advent of NGS allows identification of clonal progression earlier than morphological changes, with mutations in ASXL1 and RAS pathway genes being commonly implicated. This study supports the universal development of dedicated germline predisposition clinics. Disclosures Pruthi: CSL Behring: Honoraria; Genentech Inc.: Honoraria; Bayer Healthcare: Honoraria; HEMA Biologics: Honoraria; Instrumentation Laboratory: Honoraria; Merck: Honoraria.

Background: Chronic myelomonocytic leukemia (CMML) is a rare chronic myeloid malignancy with a poor prognosis. There are few epidemiologic studies on CMML. We studied population-based outcomes in CMML using the Surveillance, Epidemiology, and End Results (SEER) and the National Cancer Database (NCDB). Methods: The SEER 18 registries and NCDB Participant User File were used to identify patients with ICD-O-3 diagnosis code 9945/3 from 2004-2015. Incidence was identified using SEER and age-adjusted to the U.S. 2000 standard population. Causes of death were obtained and CMML-related death was defined as death from any myeloid disorder (CMML, acute monocytic leukemia, acute myeloid leukemia [AML], chronic myeloid leukemia, other myeloid/monocytic leukemia, and aleukemic, subleukemic, and NOS) to avoid misattribution. Relative survival (RS) was defined as the ratio of the proportion of observed survivors in a cohort of CMML patients to the proportion of expected survivors in a comparable set of individuals that did not have CMML, adjusting for the general survival of the US population for race, sex, age, and time when the diagnosis was established. Time to AML was calculated using the left-truncated life tables session and a 3 month latency period was used to prevent misattribution. Per the NCDB's system on classifying treatment, hydroxyurea, decitabine, and azacitidine are considered chemotherapy. The Kaplan-Meier method was used to calculate overall survival (OS), and Cox regression model was used to identify predictors of survival. Variables significant in univariate analysis (age, Charlson Deyo score [CDS], insurance type, and treatment facility type) were included in a multivariate analysis. Statistical analyses were performed using SAS version 9.0. Results: In the SEER database (n=4437), the median age at diagnosis was 76 years (interquartile range [IQR] 68-83) and 2,783 patients (63%) were male. Incidence rates (1 case/1,000,000 individuals) were as follows: overall 4.4, male 6.6, female 2.9, Non-Hispanic White 4.9, and Non-Hispanic Black 3.3. The incidence did not significantly change from 2004 to 2015. With a median follow up of 5.8 years (95% CI: 5.5-6.3), the median OS was 1.3 years (95% CI: 1.3-1.4). 3635 patients (82%) died. Among those who died, 2016 patients (55%) deaths were CMML-related. When comparing CMML patients to the US general population, 3,156 patients were matched to the expected survival tables. In the general U.S. population, the expected survival for 12, 24, 36, 48 and 60 months was 95.6%, 91.3%, 87.1%, 83.1%, and 79.2%, respectively. In contrast, the RS for patients with CMML at the same time points was 63.6%, 46.2%, 35.2%, 28.8%, and 23.1% (Figure 1). 229 patients (5.2%) progressed to AML. The median time to AML was 1.2 years (IQR 0.6-2.3). In NCDB (n=6403), the median age at diagnosis was 74 years (IQR 66-82). With the median follow up of 6 years (95% CI 3.5-9), the median OS was 1.3 years (95% CI 0.4-3.3). The distribution of CDS score 0, 1, and &gt;1 was 4518 (71%), 1193 (18%), and 692 (11%) respectively. 4687 (77%) had government insurance, while 1399 (23%) had private insurance. 3750 (60%) were treated at a non-academic center. The year of diagnosis was associated with improved OS (HR 0.99, 95% CI: 0.98-0.99). Patients who were diagnosed in 2012-2015 had improved OS compared to patients diagnosed in 2004-2007 (HR 0.89, 95% CI 0.83-0.95) with OS at 1- and 5- years being 60% and 16% (2012-2015) vs. 56% and 17% (2008-2011) vs. 53% and 15% (2004-2007) respectively. 3029 (48%) patients received chemotherapy, while 270 (4%) patients received stem cell transplant as the first-line therapy. The median time to chemotherapy from diagnosis was 19 days (IQR 6-43). OS at 1-, 5-, and 10-years was 57%, 18%, and 4% (no chemotherapy), 56%, 14%, and 7% (received chemotherapy), 79%, 44%, and 38% (received stem cell transplant), and 56%, 15%, 5% (no stem cell transplant). OS curves are shown in Figure 2. Factors independently predicting inferior OS were age ≥ 65 years at the time of diagnosis (p&lt;0.001), CDS ≥ 1 (p&lt;0.001), government insurance (p&lt;0.001), and treatment at a non-academic center (p&lt;0.001) (Table). Conclusion: Despite an improvement in survival over the years, CMML continues to be a cause of significant morbidity and mortality. Older age, CDS ≥ 1, government insurance, and treatment at non-academic facilities were predictive of inferior survival. Disclosures Shah: Dren Bio: Consultancy.

Nearly 20% of patients with myelofibrosis progress to blast phase disease; an aggressive form of acute myeloid leukemia. Although previous studies have implicated loss of TP53 or JARID2 in progression, by and large the genetic events that lead to conversion to blast phase remain unknown. To identify genes whose loss drives progression, we performed a focused CRISPR/Cas9 screen in which murine Jak2V617F bone marrow cells expressing Cas9 were transduced with two separate sgRNA libraries of known tumor suppressor genes and subjected to colony replating assays. Transduction of one of the two libraries led to serial replating and enhanced self-renewal of the Jak2V617F cells. Subsequent DNA sequencing revealed enrichment of all four guides targeting STK11, the gene that encodes LKB1 which regulates a number of key cellular pathways including energy utilization by activation of AMPK. To confirm that loss of Stk11 is the event that leads to increased clonogenicity, we collected cells from Jak2V617F/Vav-Cre+ and control Vav-Cre+ mice and induced Stk11 knockout by electroporating Cas9-Stk11 sgRNA ribonucleoprotein complexes. Consistent with the screening results, only Jak2V617F Vav-Cre+ cells with Cas9-Stk11 sgRNA showed serial replating. To determine whether Stk11 is required for growth of cells with a different driver of enhanced JAK/STAT signaling, we doubly transduced Stk11 homozygous floxed bone marrow cells with MPLW515L-mCherry and Cre-GFP to delete Stk11. As expected, cells with both MPLW515L and Cre recombinase showed enhanced self-renewal, while singly infected control cells failed to replate. These results demonstrate that activation of JAK/STAT signaling can overcome the requirement for Stk11 in normal hematopoiesis and suggest that STK11 loss may be a strong driver of malignant transformation in combination with enhanced JAK-STAT signaling. We next investigated the mechanism by which loss of STK11 cooperates with enhanced JAK/STAT signaling to promote leukemia. RNA-sequencing of wild-type, Stk11+/+/ MPLW515L, and Stk11-/-/MPLW515L hematopoietic cells revealed enrichment of a number of pathways related to hypoxia, oxidative phosphorylation and mitochondrial translation in cells lacking LKB1. Western blot assays confirmed activation of mTOR signaling as well as HIF1a stabilization and pathway activation, both of which have been reported to lie downstream of LKB1 loss. We also performed a number of studies to determine the relevance of reduced LKB1 expression to leukemic progression. First, we induced deletion of Stk11 in mice that were transplanted with HSPCs expressing MPLW515L after development of the MPN phenotype. Loss of Stk11 caused a rapid lethality that was associated with enhanced bone marrow fibrosis and osteosclerosis. We also observed accumulation of leukemic blasts in small clusters consistent with AML transformation arising in the spent phase MPN. Additionally, we deleted STK11 by CRISPR/Cas9 in primary MPN patient samples and monitored their engraftment in immunocompromised mice. We observed enhanced engraftment and increased reticulin fibrosis and osteosclerosis in mice that received the STK11 edited cells compared to those with non-targeted sgRNA. Third, we compared the expression of STK11 in paired blast and chronic phase myelofibrosis patient samples by RT-PCR. Consistent with the hypothesis that loss of STK11 facilitates leukemia, we found that its expression was decreased by more than 50% in five of seven paired post-MPN AML patient samples, with two having STK11 levels below 20%. We further validated downregulation of LKB1 by immunohistochemistry on paired chronic and blast phase MPN specimens and observed little staining in the blast phase specimens. Finally, to further show that the mechanism of in vitro enhanced self-renewal is related to leukemia progression, we stained the paired marrows for HIF1a and saw a dramatic increase in staining at the AML phase. We also analyzed RNA-seq data of paired chronic versus blast phase MPNs specimens and observed that there is a strong congruence of enriched pathways that are associated with the in vitro mouse HSPC phenotype and the human blast phase progression, such as oxidative phosphorylation and hypoxia. Together, our study demonstrates that loss of LKB1/STK11 promotes transformation of cells with activated JAK/STAT signaling and that STK11 is a prominent candidate tumor suppressor gene in post-MPN AML. Disclosures Gurbuxani: UpToDate: Honoraria. Hoffman:Dompe: Research Funding; Protagonist: Consultancy; Abbvie: Membership on an entity's Board of Directors or advisory committees; Forbius: Consultancy; Novartis: Membership on an entity's Board of Directors or advisory committees. Levine:Astellas: Consultancy; Amgen: Honoraria; Gilead: Honoraria; Qiagen: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Morphosys: Consultancy; Novartis: Consultancy; Prelude Therapeutics: Research Funding; Loxo: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Imago: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; C4 Therapeutics: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Isoplexis: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Research Funding; Roche: Consultancy, Honoraria, Research Funding; Lilly: Consultancy, Honoraria; Janssen: Consultancy. Rampal:Galecto: Consultancy; Incyte: Consultancy, Research Funding; Constellation: Research Funding; Stemline: Consultancy, Research Funding; Celgene: Consultancy; Jazz Pharmaceuticals: Consultancy; CTI Biopharma: Consultancy; Abbvie: Consultancy; Pharmaessentia: Consultancy; Promedior: Consultancy; Blueprint: Consultancy.