Al‐Kali, Aref

Abstract Venetoclax (Ven) combined with a hypomethylating agent (HMA) has now emerged as an effective treatment regimen for acute myeloid leukemia, in both de novo and relapsed/refractory setting. The current multicenter study retrospectively examined Ven + HMA treatment outcome among 32 patients (median age 69 years; 59% males) with blast‐phase myeloproliferative neoplasm (MPN‐BP). Pre‐leukemic phenotype included essential thrombocythemia (ET)/post‐ET myelofibrosis (34%), polycythemia vera (PV)/post‐PV myelofibrosis (38%) and primary myelofibrosis (28%). Twenty‐nine study patients were fully annotated cytogenetically and molecularly (NGS): 69% harbored complex karyotype and/or mutations, including TP53 (41%), IDH1/2 (21%), ASXL1 (21%), N/KRAS (14%), SRSF2 (10%), EZH2 (10%) and U2AF1 (7%). All patients received Ven combined with either azacitidine ( n = 12) or decitabine ( n = 20); either up front ( n = 23) or after failing another induction therapy ( n = 9). Complete remission with (CR) or without (CRi) count recovery was achieved in 14 (44%) patients and was more likely to occur in the absence of pre‐leukemic PV/post‐PV myelofibrosis phenotype ( p < .01), complex karyotype ( p < .01) or K/NRAS ( p = .03) mutations; seven of eight patients (88%) without vs four of 21 (19%) with complex karyotype or K/NRAS mutation achieved CR/CRi ( p < .01); all 11 informative patients with pre‐leukemic PV/post‐PV myelofibrosis phenotype displayed complex karyotype ( p < .01). In contrast, neither TP53 ( p = .45) nor IDH1/2 ( p = .63) mutations affected response. Compared to historical controls treated with HMA alone ( n = 26), the CR/CRi rate (44% vs 4%) and median survival (8 vs 5.5 months) were more favorable with Ven + HMA, but without significant difference in overall survival. Importantly, six patients with CR/CRi subsequently received allogeneic hematopoietic stem cell transplant (AHSCT). Note, Ven + HMA produces robust CR/CRi rates in MPN‐BP, especially in the absence of RAS mutations and complex karyotype, thus enabling AHSCT, in some patients.

Background: Clonal cytopenias of Undetermined Significance (CCUS) have a higher risk of progression to myeloid neoplasm (MN) compared to idiopathic cytopenias of undetermined significance (ICUS) (Malcovati et al., Blood, 2017). The implementation of flow cytometric (FC) immune-phenotyping and next generation sequencing (NGS) in clinical practice has improved the diagnosis of these entities but the clinical significance and interaction of these abnormal results are still unknown. In this study we investigated predictive factors that play role in survival and progression to MN in patients with ICUS/CCUS. Methods: Patients (Pts) who had undergone evaluation for unexplained cytopenia and had undergone FC and bone marrow morphological assessment between 3/2015-3/2020 at Mayo Clinic Rochester were included. Pts were excluded if a malignant hematological disorder was diagnosed prior to the time of FC. FC included evaluation of the following parameters: Abnormal expression of HLA-DR/CD13, CD2, CD7, CD45, and CD56 on blasts; and abnormal CD13/CD16 expression and side scatter on granulocytic cells. NGS panel up to 2018 included 34 genes, ASXL1, BCOR, BRAF, CALR, CBL, CEBPA, CSF3R, DNMT3A, ETV6, EZH2, FLT3, GATA1, GATA2, IDH1, IDH2, JAK2, KIT, KRAS, MPL, MYD88, NOTCH1, NPM1, NRAS, PHF6, PTPN11, RUNX1, SETBP1, SF3B1, TERT, TET2, TP53, U2AF1, WT1, and ZRSR2; in 2018, BRAF was omitted and 12 genes were added, ANRD26, DDX41, ELANE, ETNK1, KDM6A, MYD88, NOTCH1, RAD21, SH2B3, SRP72, SMC3, and STAG2. Results: Characteristics: Of 490 consecutive pts, 238 (median age 69 years (range 19-92), 66% males) met our inclusion criteria as ICUS. 86 (36%) pts had CCUS (abnormal cytogenetics and/or tested positive for pathogenic mutations on NGS). After a median follow-up of 28 months (95% CI: 20 to 31 months), 21 (25%) patients developed MN and 23 (27%) died during follow-up. Comparing ICUS vs CCUS: upon comparing CCUS pts to ICUS, several factors were found to be significantly different: CCUS pts were older (p= .02); majority male (p= .04), had more abnormal HLA-DR/CD13 (p &lt;.0001), more side-scattered light by FC (p &lt;.0001), more pancytopenia on follow up (p= .02) and more morphologic atypia (&lt;.0001). Overall survival (OS) outcomes in CCUS: Several covariates were significant in univariate models, and model selection was used to generate a risk score based on abnormal CD7, abnormal CD13/CD16, abnormal HLA-DR/CD13, splenomegaly and history of prior chemotherapy or radiotherapy (range: 0 - 4; HR=2.58, [95 CI: 1.69 - 3.94], p&lt;.0001). Risk scores were grouped as low risk (score=0), intermediate risk (score=1), and high risk (score=2+), with estimated 2-yr-OS of 95%, 84%, 40%, respectively (Figure 1). An extended risk score model including NGS factors added ASXL1 and IDH1 mutation status to the previous model (range: 0 - 6; HR=2.72, [95 CI 1.82 - 4.06], p&lt;0.0001). MN-free survival (MNFS) in CCUS: 37 pts either progressed to MN and/or died with a median follow up time for MNFS of 22.4 months. Similar for OS, model selection approaches yielded a composite risk score: splenomegaly, BCOR mutation status, mutation in RAS signaling pathway, abnormal expression of flow markers CD13/CD16, HLA-DR/CD13 or CD7 (HR=3.23, [95 CI: 1.90 - 5.49], p=&lt;0.0001). Risk scores were grouped as low risk (score=0), intermediate risk (score=1), and high risk (score ≥ 2), with estimated 1-yr MNFS of 84%, 74%, and 31%, respectively (Figure 2). Conclusion: CCUS has unique features compared to ICUS. Several factors, including clinical characteristics, immune-phenotyping by FC, and somatic mutations have important impact on risk of progression to MN and on overall survival. Our findings serve as proof-of-concept that such integrated models could help identify CCUS patients at higher risks for progression to MN or death. They can guide treatment accordingly and should be evaluated further. Disclosures Shah: Dren Bio: Consultancy.

Introduction Immune-mediated hematologic disorders are relatively rare but potentially life-threatening immune-related adverse events (irAE) with immune checkpoint inhibitor (ICI) therapy (Shiuan, Beckermann et al 2017). The management strategy often relies on systemic corticosteroids and other immunosuppressant agents in steroid-refractory cases (Brahmer, Lacchetti et al 2018). We hereby describe our institution's experience in diagnosing and managing immune-related hematologic adverse events (ir-h-AE). Methods We retrospectively searched the electronic health record for all ir-h-AE diagnosed by treating providers and confirmed by study authors between 2015 and 2020. The search included patients on ICI and the following conditions: immune-related neutropenia (IRN), autoimmune hemolytic anemia (AIHA), cold agglutinin disease (CAD), immune thrombocytopenia (ITP), immune-related pancytopenia, aplastic anemia (AA), and pure red cell aplasia (PRCA). For AIHA, PRCA, and CAD, partial response (PR) was defined as hemoglobin greater than 10 g/dL but &lt; 12 g/dL and 2 g/dL above the nadir without blood product transfusion. Complete response (CR) was defined as hemoglobin of ≥ 12 g/dL and 2 g/dL above the nadir without blood product transfusion (Peñalver, Alvarez-Larrán et al. 2010). For ITP, CR was defined as platelet count ≥ 100 × 109/L and absence of bleeding. PR was defined as platelet count ≥ 30 × 109/L and ≥ two-fold increase from the baseline count and absence of bleeding (Gómez-Almaguer, Tarín-Arzaga et al. 2013). For IRN, CR was defined as absolute neutrophil count (ANC) ≥ 1500/ mm3 on 2 consecutive measurements separated by 7 days; PR was defined as ANC ≥ 500/ mm3 sustained over 7 days. JMP® 14.1 was used for data analysis. Results Seventeen patients were identified, 9 (52.9%) of whom were female (table 1). Median age was 68 years (range 26-78). The most common pre-existing malignancies were melanoma (6 patients, 35.3%), non-small cell lung cancer (4 patients, 23.5%), and gastrointestinal cancer (3 patients, 17.6%). The ir-h-AE included 7 patients (41.2%) with warm AIHA, 4 (23.5%) with ITP (1 had immune-related pancytopenia that resolved with ITP persisting), 3 (17.6%) with IRN, 1 with AA, 1 with CAD, and 1 with PRCA and mild ITP. All patients had received an ICI dose within 60 days of diagnosis (range 3-52 days, median 18 days). Only 1 patient had a concomitant chronic autoimmune disorder (antinuclear antibody-positive arthritis). Four patients (23.5%) were receiving chemotherapy. Sixteen patients (94.1%) required treatment and received corticosteroids. Eight out of 15 evaluable patients (53.3%) responded to corticosteroids only. Another 4 responders (26.7%) required additional therapies including intravenous immunoglobulins (IVIG) (4, 23.5%) and/or rituximab (4, 23.5%). Overall response rate was 71.4% for AIHA and 100% for IRN. ITP was likely underrepresented in our cohort, and the response rate of 66.7% is likely lower than the response rate in clinical practice. This could be related to the fact that many mild thrombocytopenia cases are not further evaluated in clinical practice. None of our patients died from the sequelae of an ir-h-AE. Two patients (11.8%) died within 30 days of ir-h-AE diagnosis (disseminated intravascular coagulation likely due to the underlying malignancy and sepsis from bacterial pneumonia). At the time of ir-h-AE diagnosis, the malignancy was showing evidence of response in 9 patients (52.9%), progression in 6 patients (35.3%), and stability in 2 patients (11.8%). ICI therapy was permanently discontinued in 9 patients (52.9%) and temporarily held in 6 patients (35.3%). Three of the 5 patients (60%), who were rechallenged with ICI therapy, had recurrence of the same ir-h-AE (AIHA) with adequate response to therapy. Non-hematologic irAE (7 patients, 41.2%) included 3 patients with hepatitis, 2 with thyroiditis, 2 with pneumonitis, 1 with colitis, and 1 with dermatitis. Conclusion Our clinical experience with ir-h-AE highlights the importance of exercising vigilance in assessing the hematologic parameters of patients receiving ICI therapy. While relatively rare, ir-h-AE may impact the clinical course of patients with cancer and their eligibility for therapies that have the potential of offering durable control of the underlying malignancy. ir-h-AE respond to classical therapies including corticosteroids, IVIG, and rituximab. Disclosures Block: Merck: Research Funding; Bristol-Myers Squibb: Research Funding; Genentech: Research Funding; Pharmacyclics: Research Funding; Marker Therapeutics: Research Funding; Transgene: Research Funding; Immune Design: Research Funding. Kottschade:Bristol-Myers Squibb: Consultancy, Research Funding.

Abstract Objectives SF3B1 mutations are the most common mutations in myelodysplastic syndromes (MDS). The International Working Group for the Prognosis of MDS (IWG-PM) recently proposed SF3B1-mutant MDS (SF3B1-mut-MDS) as a distinct disease subtype. We evaluated the spectrum and molecular landscape of SF3B1-mutated myeloid disorders and assessed the prognostication in MDS harboring SF3B1 mutations (MDS-SF3B1). Methods Cases were selected by retrospective review. Clinical course and laboratory and clinical findings were collected by chart review. SF3B1-mut-MDS was classified following IWG-PM criteria. Results SF3B1 mutations were identified in 75 of 955 patients, encompassing a full spectrum of myeloid disorders. In MDS-SF3B1, Revised International Prognostic Scoring System (IPSS-R) score greater than 3 and transcription factor (TF) comutations were adverse prognostic markers by both univariate and multivariate analyses. We confirmed the favorable outcome of IWG-PM-defined SF3B1-mut-MDS. Interestingly, it did not show sharp prognostic differentiation within MDS-SF3B1. Conclusions SF3B1 mutations occur in the full spectrum of myeloid disorders. We independently validated the favorable prognostication of IWG-PM-defined SF3B1-mut-MDS. However it may not provide sharp prognostication within MDS-SF3B1 where IPSS-R and TF comutations were prognostic-informative. Larger cohort studies are warranted to verify these findings and refine MDS-SF3B1 prognostication.

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 T-cell prolymphocytic leukemia (T-PLL) is a rare, aggressive malignancy of mature T-cells. Although responses may been seen with initial alemtuzumab-based therapy, relapse is inevitable and relapsed/refractory disease carries a dismal prognosis. T-PLL has shown in vitro sensitivity to venetoclax, and short-lived clinical responses to venetoclax monotherapy (Smith, Blood Advances 2020; Boidol, Blood 2017) or when given in combination with pentostatin (Alfayez, Leukemia & Lymphoma 2020). Given the lack of standard treatment options, we reviewed the outcomes of patients (pts) with relapsed T-PLL on venetoclax-based therapy. METHODS Using an institutional clinical database of pts with T-PLL seen in the Division of Hematology at Mayo Clinic, Rochester, MN, all pts treated with venetoclax or venetoclax-based therapies in a relapsed/refractory setting were identified. Clinical, laboratory, and pathology data, as well as treatment dosing and toxicity were ascertained retrospectively from the medical records. Diagnostic criteria and response definitions were utilized as per the T-PLL International Study Group (Staber, Blood 2019). RESULTS Between 8/2017 and 5/2020, 9 pts with relapsed/refractory T-PLL treated with venetoclax were identified. The median age was 63 years (range 49-75), and one-third were male. Baseline characteristics are detailed in Table 1. Rearrangement of TCL1 family genes was present in all 8 pts evaluated with fluorescence in situ hybridization (FISH). Using conventional cytogenetics, a complex karyotype was present in 4/6 pts tested. The median prior lines of therapy was 3 (range 1-4), including alemtuzumab in 8 of 9 pts (intravenous 7/8); and two pts had undergone prior hematopoietic stem cell transplantation (1 allogeneic; 1 autologous) after achieving a complete remission. Additional individual pt details are included in Table 2. Prior to venetoclax therapy initiation, 2 pts had B-symptoms (2 night sweats; 1 fever) and 6 pts had an ECOG score ≥ 2. Lymphadenopathy and splenomegaly were present in 6 and 9 pts, respectively. Extranodal involvement included 3 pts with cutaneous involvement and 5 pts with effusions (4 ascites; 1 pleural). The target maximum dose of venetoclax (800 mg [n=4]; 400 mg [n=1]) was reached by 5 pts at a median of 12 days (range 7-40 days). The other 4 pts had disease progression after a median of 10 days (range 5-22 days) during the dose ramp-up, including 2 pts undergoing rapid dose escalation. Altogether, 6 of the 9 pts initiated venetoclax with a rapid dose escalation. Bendamustine was given with venetoclax in 5/9 pts; median number of cycles 1 (range 1-4) with variable starting dosing (range 60-100 mg/m2). The disease control rate was 56%; best response was partial remission (PR) in 4 (44%) pts and stable disease (SD) in 1 (11%) pt. The 1 pt with SD received venetoclax monotherapy; however, the overall response rate among pts who received the combination of venetoclax and bendamustine was 80% (4/5 pts). One pt with a partial remission met all criteria for complete remission but did not have a confirmatory bone marrow biopsy. Cutaneous disease improved in 2 of 3 pts (both with PR as best response), and effusions improved in 2 of 5 pts (1 PR and 1 SD as best response). Among those in PR, the median decrease in absolute lymphocyte count was 67x109/L and the median decrease in lactate dehydrogenase was 1,162 U/L (normal range 122-222 U/L). Median duration of treatment for all pts was 42 days (range 4-201 days). All pts ultimately died during follow-up with a median overall survival of 53 days (range 4-464 days); Figure 1. All pts experienced at least one adverse event and 8 of 9 pts had a grade ≥ 3 toxicity, most commonly edema (n=7) and neutropenia (n=6). Five pts required dose interruptions due to neutropenia (n=3), tumor lysis syndrome (n=1), and edema (n=1). Three pts had dose reductions, all from 800 mg dosing, due to hematologic toxicity (n=2) and nausea (n=1). No pts discontinued venetoclax as a result of adverse events. CONCLUSION Treatment of pts with relapsed/refractory T-PLL remains a significant unmet need. The 9 pts described herein represent the largest cohort of pts treated with venetoclax-based therapy in this setting to the current date. Despite initial reports of clinical efficacy, our results show that venetoclax (with or without bendamustine) has modest efficacy in the treatment of relapsed/refractory T-PLL after prior alemtuzumab exposure. Disclosures Parikh: TG Therapeutics: Research Funding; Verastem Oncology: Honoraria; GlaxoSmithKline: Honoraria; AbbVie: Honoraria, Research Funding; Genentech: Honoraria; Merck: Research Funding; MorphoSys: Research Funding; Pharmacyclics: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Ascentage Pharma: Research Funding; AstraZeneca: Honoraria, Research Funding. Shah:Dren Bio: Consultancy. Bennani:Verastem: Other: Advisory Board; Affimed: Research Funding; Purdue Pharma: Other: Advisory Board; Kite/Gilead: Research Funding. Wang:Incyte: Research Funding; Novartis: Research Funding; Innocare: Research Funding. Kenderian:MorphoSys: Research Funding; Lentigen: Research Funding; Gilead: Research Funding; Juno: Research Funding; BMS: Research Funding; Tolero: Research Funding; Sunesis: Research Funding; Kite: Research Funding; Novartis: Patents & Royalties, Research Funding; Torque: Consultancy; Humanigen: Consultancy, Patents & Royalties, Research Funding; Mettaforge: Patents & Royalties. Kay:MEI Pharma: Research Funding; Oncotracker: Membership on an entity's Board of Directors or advisory committees; Abbvie: Research Funding; Morpho-sys: Membership on an entity's Board of Directors or advisory committees; Acerta Pharma: Research Funding; Cytomx: Membership on an entity's Board of Directors or advisory committees; Juno Theraputics: Membership on an entity's Board of Directors or advisory committees; Dava Oncology: Membership on an entity's Board of Directors or advisory committees; Bristol Meyer Squib: Membership on an entity's Board of Directors or advisory committees, Research Funding; Tolero Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Rigel: Membership on an entity's Board of Directors or advisory committees; Agios Pharma: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sunesis: Research Funding; Astra Zeneca: Membership on an entity's Board of Directors or advisory committees. Ding:Octapharma: Membership on an entity's Board of Directors or advisory committees; Astra Zeneca: Research Funding; alexion: Membership on an entity's Board of Directors or advisory committees; Beigene: Membership on an entity's Board of Directors or advisory committees; MEI Pharma: Membership on an entity's Board of Directors or advisory committees; Merck: Membership on an entity's Board of Directors or advisory committees, Research Funding; DTRM: Research Funding; Abbvie: Research Funding. OffLabel Disclosure: Venetoclax: off-label use in treatment of relapsed/refractory T-cell prolymphocytic leukemia

Background: Gilteritinib is approved for the treatment of relapsed/refractory (R/R) AML and FLT3-mutation (FLT3mut+). However, the gilteritinib phase 3 ADMIRAL study (Perl et al NEJM 2019) enrolled prior to widespread adoption of either midostaurin as a component of standard intensive induction and consolidation or post-transplant FLT3inhibitor (FLT3i) maintenance. Some mechanisms of drug resistance can be shared across FLT3i's, suggesting response to gilteritinib might differ in patients treated with frontline FLT3i. A better understanding of how prior therapy modulates response to gilteritinib is necessary to clarify this novel agent's role in the current FLT3-mutated AML treatment algorithm. Methods: This is an ongoing multi-institutional analysis from 13 US centers identifying patients who received gilteritinib alone or as combination therapy for the treatment of R/R FLT3mut+ AML. Patients who received gilteritinib as a part of an ongoing trial were excluded. Response criteria were identical to the ADMIRAL trial. For patients with available data and a composite complete remission (CRc), we defined clinically measurable residual disease (cMRD) negative status by bone marrow flow cytometry using a cutoff of &lt;1 x 10x105 cells as well as polymerase chain reaction (PCR) for FLT3 mutation with a minimum sensitivity of 5%. Survival from the time of gilteritinib initiation was recorded. Multivariate analysis included all variables collected to determine interaction with patient outcome (CR and survival data). Kaplan-Meier curves and log rank test were used for survival analysis after gilteritinib initiation. Results: 72 patients treated with prior FLT3i exposure received gilteritinib for treatment of R/R FLT3mut+ AML. Patient characteristics are presented in table-1 with 46 (64%) previously receiving midostaurin, 19 (26%) sorafenib, and 7 (10%) other FLT3i. 8 (11%) received more than one prior TKI. NGS at diagnosis were available in 66 patients (92%) and co-mutations in DNMT3A, NPM1 and NRAS were observed in more than 10% of patients. Average duration of gilteritinib therapy was 5.7 months (range: 0.2-25 months). 27 (37.5%) received stem cell transplant (SCT) before gilteritinib and 15 (21%) underwent SCT after gilteritinib. The composite CR rate (CRc, defined as CR + CRi + CRp) was 51.4% (n= 37 patients). With regard to specific FLT3i's, we found no significant difference in median survival (7.1 months and 6.4 months for midostaurin and sorafenib, respectively) or remission rates (CRc 54% and 47% for prior midostaurin and sorafenib, respectively). The CRc rate for patients who received only prior 7+3 and midostaurin with or without consolidation was 58% with a median survival of 7.8 months. A trend toward higher CRc rate was noted in patients treated with gilteritinib in combination regimens rather than as a single agent (64% vs 43%, respectively, p=0.09 using Chi-square test). No survival advantage for combination therapy was seen over single agent. Survival was longest in patients who obtained a CR, particularly a cMRD negative response; this remained significant after censoring at the time of SCT (figures 1&2). Patients who received SCT after gilteritinib had significantly longer survival than non-transplanted patients (9.3 months vs 5.6 months, respectively, HR 0.44, 95% CI 0.2-0.8)(figure-3). Patients with concurrent mutations of NPM1/DNMT3A had a trend toward a higher CRc compared to FLT3 mutation alone (71% vs 50%, p= 0.2) but similar survival. With regard to mutations associated with drug resistance to other FLT3i's, patients with both FLT3-ITD and FLT3-D835 mutation had similar response and survival to FLT3-ITD alone. However, patients with MAPK pathway activating mutations (e.g. NRAS and PTPN11) had lower CRc (37.5% vs 59.5%) and poorer median survival than other patients (3.3 months vs 7.5 months) (HR 2.2- 95% CI 1.1-4.4) p value &lt;0.01(figure-4). Conclusions: In this multi-center, retrospective analysis, gilteritinib remains a clinically active agent after treatment failure of prior FLT3i's (midostaurin or sorafenib). Mutations activating MAPK pathway have been implicated in secondary gilteritinib resistance but are seldom co-mutated at initial FLT3mut+ AML diagnosis. While further study is required, we hypothesize that their detection after frontline FLT3i therapy may represent treatment-emergent clones with propensity for pan-FLT3i resistance. Disclosures Zeidan: Cardiff Oncology: Consultancy, Honoraria, Other; Trovagene: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding; Otsuka: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria, Research Funding; Boehringer-Ingelheim: Consultancy, Honoraria, Research Funding; Celgene / BMS: Consultancy, Honoraria, Research Funding; Jazz: Consultancy, Honoraria; Daiichi Sankyo: Consultancy, Honoraria; BeyondSpring: Consultancy, Honoraria; Seattle Genetics: Consultancy, Honoraria; Taiho: Consultancy, Honoraria; Cardinal Health: Consultancy, Honoraria; Acceleron: Consultancy, Honoraria; Astellas: Consultancy, Honoraria; Aprea: Research Funding; ADC Therapeutics: Research Funding; MedImmune/Astrazeneca: Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Ionis: Consultancy, Honoraria; Epizyme: Consultancy, Honoraria; Astex: Research Funding; CCITLA: Other; Leukemia and Lymphoma Society: Other; Agios: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding; Incyte: Consultancy, Honoraria, Research Funding. Yilmaz:Pint Pharma: Honoraria; Pfizer: Research Funding; Daicho Sankyo: Research Funding. Foran:Agios: Honoraria, Research Funding; H3Biosciences: Research Funding; Xencor: 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. Daver:Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Syndax: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; KITE: Consultancy, Membership on an entity's Board of Directors or advisory committees; Agios: 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, Research Funding; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Karyopharm: Research Funding; Servier: Research Funding; Genentech: Research Funding; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novimmune: Research Funding; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Trovagene: Research Funding; Fate Therapeutics: Research Funding; ImmunoGen: Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz: Consultancy, Membership on an entity's Board of Directors or advisory committees; Trillium: Consultancy, Membership on an entity's Board of Directors or advisory committees. Perl:Novartis: Honoraria, Other, Research Funding; Agios: Consultancy, Honoraria, Other; Biomed Valley Discoveries: Research Funding; Jazz: Honoraria, Other; FORMA Therapeutics: Consultancy, Honoraria, Other; Syndax: Consultancy, Honoraria; Actinium Pharmaceuticals Inc: Consultancy, Honoraria, Research Funding; AbbVie Inc: Consultancy, Honoraria, Other, Research Funding; Loxo Oncology Inc, a wholly owned subsidiary of Eli Lilly & Company: Consultancy, Honoraria, Other; Bayer HealthCare Pharmaceuticals: Research Funding; New Link Genetics: Honoraria, Other; Astellas: Consultancy, Honoraria, Other: writing/editorial support, travel costs for meeting presentations related to study, Research Funding; Daiichi Sankyo: Consultancy, Honoraria, Other: Writing/editorial support, travel costs for meetings, Research Funding; Leukemia & Lymphoma Society, Beat AML: Consultancy; Arog Pharmaceuticals Inc: Other: uncompensated consulting, travel costs for meetings; FUJIFILM Pharmaceuticals USA, Inc: Research Funding; Takeda: Honoraria, Other: Travel costs for meeting. Altman:Kartos: Research Funding; Celgene: Research Funding; Boehringer Ingelheim: Research Funding; ImmunoGen: Research Funding; Amgen: Research Funding; Aprea: Research Funding; Amphivena: Research Funding; Genentech: Research Funding; Novartis: Consultancy; Syros: Consultancy; Janssen: Consultancy; Immune Pharmaceuticals: Consultancy; ASH: Consultancy; Bristol-Myers Squibb: Consultancy; Glycomimetics: Other: Data safety and monitoring committee; Daiichi Sankyo: Other: Advisory Board - no payment but was reimbursed for travel; Kura Oncology: Other: Scientific Advisory Board - no payment accepted, Research Funding; BioSight: Other: No payment but was reimbursed for travel , Research Funding; AbbVie: Other: advisory board, Research Funding; Agios: Other: advisory board, Research Funding; Theradex: Other: Advisory Board; Astellas: Other: Advisory Board, Speaker (no payment), Steering Committee (no payment), Research Funding; PrIME Oncology: Consultancy; PeerView: Consultancy; Cancer Expert Now: Consultancy; France Foundation: Consultancy; Fujifilm: Research Funding. OffLabel Disclosure: Some of the patients we are reporting on received gilteritinib in combination with other agents which is off-label use.