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BACKGROUND Pulmonary infiltrates are common after allogeneic hematopoietic cell transplantation (HCT) and can have infectious or non-infectious etiologies. Fiberoptic Bronchoscopy (FOB) with bronchoalveolar lavage (BAL) is frequently used to evaluate these patients. However, the diagnostic yield can be highly variable according to patient populations, and the impact on management is not well defined, especially in the era of modern antimicrobial therapies. The aim of this study was to investigate the diagnostic and therapeutic yield of FOB-BAL in adult patients with pulmonary infiltrates during the first 100 days following HCT. METHODS We retrospectively reviewed the medical records of adult HCT patients who underwent FOB-BAL during the first 100 days post HCT between January 2005 and December 2015 at Mayo Clinic, Rochester, MN. The interval from HCT to FOB was stratified into early (days 1-30) vs. late (days 31-100). The finding of progressively more hemorrhagic effluent and/or ≥ 20% hemosiderin-laden macrophages in BAL were considered diagnostic for diffuse alveolar hemorrhage (DAH). Univariate and multivariate logistic regression models were fit to identify clinical and transplant characteristics that may impact the diagnostic yield of FOB-BAL. RESULTS A total of 114 patients (median age 55 years), representing 12% of all HCT patients underwent FOB-BAL. Underlying diagnoses were AML in 36%, MDS in 16%, ALL in 16%, MPN in 12% , CLL in 7%, and other in 13%. Transplants were from matched related donor in 43%, matched unrelated donor in 40%, and other donor/matching status in 17%. FOB-BAL was performed during the early period in 61% and during the late period in 39% of patients. In the early period, FOB-BAL provided a specific diagnosis in 49% of patients (30% DAH and 19% infection). In the late period, FOB-BAL had a diagnostic yield of 55% (14% DAH and 36% infection) (Figure 1). The distribution of bacterial and viral infections identified via BAL were similar during the early period (39% and 38%, respectively), whereas more bacterial than viral infections were identified in the later period (56% vs. 19%, respectively) (Figure 2). Non-invasive testing for respiratory tract infection was performed in 34% of patients. These included nasopharyngeal swab for RSV/Influenza PCR in 16% (all negative), multiplex respiratory pathogen PCR in 5% (1 positive for coronavirus), and sputum culture in 21% (positive in 8 patients). This compares with the identification of an infectious pathogen via BAL in 36% of patients; bacterial in 16%, viral in 11%, and fungal in 10%. Transbronchoscopic lung biopsy biopsies were performed in 8 patients and provided diagnostic information in 3 patients (eosinophilic pneumonia, organizing pneumonia and diffuse alveolar damage each in 1 patient). Procedural complications occurred in 3 patients; 2 after transbronchoscopic lung biopsy (1 bleeding and 1 pneumothorax) and 1 during FOB-BAL (atrial fibrillation with rapid ventricular rate). In a multivariable logistic regression model, the underlying diagnosis, presence of acute respiratory failure, and early vs. later time period after HCT were independently affecting the diagnostic yield of FOB-BAL, with higher likelihood of DAH being diagnosed in patients with AML/MDS and during the early post-HCT period, and higher likelihood of DAH being diagnosed in patients with acute respiratory failure (Table 1). In 40% of patients, FOB-BAL findings lead to treatment changes. These included addition of antimicrobials in 24% and addition of corticosteroids in 22% (17% DAH, 2% idiopathic pneumonia syndrome, and 1% organizing pneumonia) (Figure 3). FOB findings lead to more antimicrobial modifications in the early than in the later period (32% vs. 18%, respectively). Overall survival was poor in all the three groups, although significantly better in patients with non-diagnostic FOB findings (median of 2, 3, and 11 months in patients with DAH, infection, or non-diagnostic FOB finings, respectively) (p = 0.03) (Figure 4). CONCLUSION FOB-BAL provides clinically useful information in the post-transplant period. BAL findings were diagnostic in 51% of patients, and led to management changes in 40% of patients. Transbronchoscopic lung biopsy is associated with higher rates of procedural complications. Further characterization of the underlying diagnosis in patients with non-diagnostic FOB-BAL findings remains an unmet clinical goal. Disclosures Sakemura: Humanigen: Patents & Royalties. Kenderian:Morphosys: Research Funding; Kite/Gilead: Research Funding; Lentigen: Research Funding; Humanigen: Other: Scientific advisory board , Patents & Royalties, Research Funding; Tolero: Research Funding; Novartis: Patents & Royalties, Research Funding. Patnaik:Stem Line Pharmaceuticals.: Membership on an entity's Board of Directors or advisory committees.

Introduction There have been few recent therapeutic advances in T-acute lymphoblastic leukemia/lymphoma (T-ALL/LBL), a rare and aggressive malignancy. Intensive chemotherapy +/- allogeneic transplantation (AlloHCT) can effect cure, realized by only a minority of adults. In distinction to B-ALL, there have been no safe/effective targeted therapies developed in T-ALL/LBL. We therefore performed a focused tissue array to identify novel tumor proteins, including CCR4; evaluated together with established immunophenotypic (IP) T-ALL/LBL subtypes [early-T-precursor (ETP), early non-ETP (Pre/Pro-T), common & late thymocyte]. We evaluated the clinical phenotype and outcome together with clinical and epidemiologic data in patients diagnosed at the 3-site Mayo Clinic Cancer Center (MCCC: Rochester, MN; Phoenix, AZ; and Jacksonville, FL). Methods Following IRB approval, we identified 50 consecutive T-ALL/LBL patients from 1997 -2019 diagnosed at the 3-site MCCC. Available remnant leukemia/lymphoma paraffin blocks were identified (n=28). Using immunohistochemistry (IHC) we evaluated expression of leukemic antigens of interest (CCR4, CD47, BCL2, BCL6, PD-L1, CD38 and CD123); these were selected based on clinical availability of novel targeted agents, approved or in development for other indications. Tissue array studies were performed and interpreted by a single hematopathologist (L.J) blinded to clinical data, using positive and negative controls, according to standard techniques. We also evaluated the clinical and epidemiological parameters, including different IP subtypes [ETP: CD1a-, sCD3- & CD8-, Pre/Pro-T: CD1a-, sCD3- & CD8+ or CD8- (11 marker T-ALL IP score was used to distinguish CD8- ETP vs. Pre/Pro-T), thymic: CD1a+ and mature: CD1a- & sCD3+] (Khogeer et al., Br J Haematol., 2019) & the presence of the unique MLLT10-PICALM fusion (n=6), as well as therapy and outcome. Comparisons of characteristics and outcomes of interest were made using a Wilcoxon rank sum test (continuous characteristics) or Fisher's exact test (categorical characteristics), unadjusted Cox proportional hazards regression models (overall survival), or unadjusted logistic regression models (complete remission after first line treatment). Results We identified the expression of novel targetable tissue proteins in all adult T-ALL/LBL cases [Table 1]. BCL2, CD38 & CD47 were expressed in majority of the cases, and CCR4 [Fig. 1] was expressed in 11/28 (39.3%) cases. CCR4 expression was significantly more common in the Pre/Pro-T (75%) vs. other IP subtypes (19%) (p=0.011); there was no other association of CCR4 expression with clinical characteristics/outcomes. We also observed differences in T-ALL vs. T-LBL, specifically T-ALL patients were more likely to be male (71% vs. LBL 38.9%, p=0.038). Surprisingly, T-LBL patients were more likely to have a family history of leukemia/lymphoma (41.2% vs. T-ALL 0%, p<0.001). In addition, a significantly different distribution of IP subtype in T-LBL was noted [Table 2]. Not surprisingly, T-LBL patients were more likely to receive 1st line Hyper-CVAD therapy (88.2% v. T-ALL 43.3%, p=0.005), & had a longer delay from diagnosis to initiation of therapy (median 14 vs. 4 days, p=0.012), however this did not appear to impact clinical outcome. In contrast, we observed an important association of IP subtype with outcome after therapy, including complete remission (p=0.035), & a trend suggesting differences in survival (p=0.069) [Table 3]. However, MLLT10-PICALM was not associated with any unique clinical features or with outcome (death, p=0.85; CR, p=0.98), although 4/6 patients underwent AlloHCT, suggesting an important role of AlloHCT in this subgroup. No other significant association of epidemiologic risk factors with phenotype or outcome was noted. Conclusion Using focused tissue array we have identified expression of tumor associated proteins in T-ALL/LBL including CCR4 (Pre/Pro-T IP) & others, which may be targets of therapeutic agents like mogamulizumab. Furthermore, our analysis demonstrates an important clinical impact of IP subtype in T-ALL/LBL, as well as important clinical & therapeutic differences in T-ALL vs. LBL. This study will help guide development of targeted clinical trials in T-ALL/LBL (CCR4 trial already in development). Further analyses are planned to determine the clinical & epidemiologic association of genetic lesions in this cohort. Disclosures Foran: Agios: Honoraria, Research Funding.

Background: Myelodysplastic syndrome (MDS)/myeloproliferative neoplasm (MPN) with ring sideroblasts and thrombocytosis (MDS/MPN-RS-T) was formally included as a unique WHO-defined entity in the 2016, iteration of the classification of hematological neoplasms (under MDS/MPN overlap syndromes). Patients with MDS/MPN-RS-T have features of MDS-RS-single lineage dysplasia (SLD), persistent thrombocytosis (platelet count ≥450x109/L), with proliferation of large atypical megakaryocytes. Anemia, including red blood cell transfusion dependency (RBC-TD) is a major problem. While extensive studies have documented erythroid response rates (ERR) to erythropoiesis stimulating agents (ESA) in MDS and MDS-RS-SLD, the data in MDS/MPN-RS-T is less clear. We carried out this study to asses ERR in ESA treated patients with MDS/MPN-RS-T. Methods: After approval by the IRB, patients with 2016, WHO-defined MDS/MPN-RS-T were included in the study. The bone marrow (BM) morphology, cytogenetics and BM RS% were retrospectively reviewed. All study patients underwent next generation sequencing for 29 myeloid-relevant genes, obtained on BM mononuclear cells, at diagnosis, or at first referral, by previously described methods (Patnaik et al., BCJ 2016). Treatment details, including the type of ESA used, dose administered, side effects and reason for discontinuation were retrospectively abstracted. Erythroid responses were assessed using the 2006, international working group (IWG) MDS and the 2015, IWG MDS/MPN response criteria. Results: Forty seven patients with MDS/MPN-RS-T were identified, of which 37 (79%) patients received ESA treatment at any time point during their disease course; median age 73 years (range, 52-93), 46% male.The hemoglobin at diagnosis (HB) and baseline erythropoietin (EPO) levels were 9.1 gm/dL (range, 6.6-12.1) and 39 IU/L (range, 8-500), respectively. Ten (29%) patients were RBC-TD at baseline. None of the 37, ESA-treated patients were on concomitant cyto-reductive therapy for thrombocytosis. Twenty (54%) patients were treated with erythropoietin-a, 13 (35%) with darbepoetin, and 4 (11%) with both sequentially. Median doses were 40,000 IU weekly (range, 20,000-80,000) for erythropoietin-a and 200 mcg every 2 weeks (range, 100-500), for darbepoetin. Median treatment duration was 14 months (range, 1-173) and causes for discontinuation included; ESA failure/loss of response in 20 (54%), sustained HB rise in 1 (3%) and other causes, including adverse events in 4 (11%) patients. With regards to safety, the following events were considered potentially ESA related; treatment emergent hypertension in 2 (5%), venous thromboembolism, ischemic stroke and splenic infarction in 1 (3%) patient each, respectively. All patients with thrombotic/ischemic events had been on low dose aspirin prophylaxis. Erythroid responses by the IWG MDS and MDS/MPN response criteria were assessable in 35 (95%) patients: with 16 (46%) meeting criteria for an erythroid response, by both assessment systems. The median duration of ER was 20 months (range, 2-172). In comparison to ESA non-responders, those that responded were more likely to have baseline EPO levels ≤44 IU/L (ROC analysis; median, 28 vs 112 IU/L; p=0.0080), while there was a trend for inferior responses associated with RBC-TD (p=0.0857). Age, gender, baseline white blood cell and platelet counts, type of ESA used, BM RS %, JAK2V617F, SF3B1, DNMT3A, TET2 and ASXL1 mutational status did not impact ESA response (Table 1). On a univariate survival analysis (OS), survival was not significantly different between ESA responders vs non-responder (median OS, 76 vs 45 months; p=0.2929). After ESA failure, 7 (19%) patients received hypomethylating agents (HMA), while 5 (14%) received lenalidomide. There were no erythroid responses to HMA, while 1 of 3 (33%) assessable lenalidomide treated patients achieved a morphological complete response. Conclusion: Erythropoiesis stimulating agents are effective first line therapies for the management of anemia in patients with MDS/MPN-RS-T, with 46% achieving an erythroid response (median duration of response of 20 months). Low baseline endogenous EPO level (<44 IU/L) was the best predictor of response, with a trend towards an inferior response in the presence of RBC-TD. In the context of clonal thrombocytosis, potentially related thrombotic/ischemic events were documented in 8% of patients. Disclosures Al-Kali: Astex Pharmaceuticals, Inc.: Research Funding. Patnaik:Stem Line Pharmaceuticals.: Membership on an entity's Board of Directors or advisory committees.

Patients who develop therapy-related myelodysplastic syndromes (t-MDSs) or acute myeloid leukemia (t-AML) following prior chemotherapy or an autologous hematopoietic cell transplant (HCT), have a poor prognosis. An earlier analysis of allogeneic HCT (n=868, 1990-2004) showed 5-year overall survival (OS) and disease free survival (DFS) were 22% and 21% (reference). Furthermore, older age, graft source other than a HLA-matched sibling or HLA well matched unrelated donor (URD), t-AML not in remission or advanced t-MDS, and poor risk cytogenetics were associated with worse outcomes. Modern supportive care and conditioning regimens including reduced intensity (RIC) regimens may have improved outcomes. Therefore we analyzed 1531 HCT for t-AML (n = 772) or t-MDS (n = 759) performed from 2000 to 2014. The median age at transplant was 52 (18-77) for t-AML and 59 (18-74) for t-MDS. Eleven percent of patient with t-AML and 24% of patient with t-MDS had a prior autologous transplant. A myeloablative regimen was used for conditioning in 61% of patients with t-AML and 49% of patients with t-MDS (Table 1). For t-AML, the 5-year non-relapse mortality (NRM) and relapse rates (RR) were 33% (95% confidence interval [CI], 30-36) and 43% (40-47), respectively. For t-MDS, the 5 year TRM and RR were 32% (29-36) and 46% (43-50), respectively. Five year DFS and OS were 24% (21-27) and 25% (22-28), respectively, for patients with t-AML. Five year DFS and OS were 21% (18-24) and 27% (23-31), respectively, for patients with t-MDS. In multivariate analysis, t-AML OS and DFS was worse for: previous autologous transplant, relapsed disease at HCT, intermediate or adverse cytogenetics, partially matched and cord blood grafts, and RIC. For t-MDS: age greater than 60, previous autologous transplant, very high IPSS score, and use of HLA-partially matched unrelated grafts. A significant minority of patients with t-AML and t-MDS can achieve long-term remission with allogeneic HCT, yet risks of both NRM and relapse are still excessive. Relapse is the major cause of treatment failure. Disclosures Metheny: Takeda: Speakers Bureau; Incyte: Speakers Bureau. Weisdorf:Incyte: Research Funding; Fate Therapeutics: Consultancy; Pharmacyclics: Consultancy. Kebriaei:Jazz: Consultancy; Amgen: Research Funding; Pfizer: Honoraria; Kite: Honoraria.

Introduction: Myelodysplastic syndrome/myeloproliferative neoplasm (MDS/MPN) overlap syndromes consist of 5 distinct WHO-defined entities; namely chronic myelomonocytic leukemia (CMML), atypical chronic myeloid leukemia, BCR/ABL1- (aCML), juvenile myelomonocytic leukemia (JMML), MDS/MPN with ring sideroblasts and thrombocytosis (MDS/MPN-RS-T), and MDS/MPN, unclassifiable (MDS/MPN-U) (Arber et al., Blood 2016). With the notable exception of JMML, a bona fide RASopathy, the other entities are characterized by clinical heterogeneity and molecular diversity. Loss of function TET2 mutations (TET2MT) are common in myeloid neoplasms, especially CMML (60%), and are known leukemogenic drivers. We carried out this study to assess the TET2 mutational landscape and phenotypic correlates in patients with MDS/MPN overlap syndromes. Methods: After approval by the institutional review board, adult patients with WHO defined MDS/MPN overlap syndromes were included; with the exception of JMML. The BM morphology, cytogenetics and 2016, WHO-diagnoses were retrospectively reviewed and all patients underwent targeted next generation sequencing for 29 myeloid-relevant genes, obtained on BM mononuclear cells, at diagnosis, or at first referral, by previously described methods (Patnaik et al., BCJ 2016). Results: Five hundred and four patients were included in the study; including 387 (77%) with CMML, 48 (10%) with MDS/MPN-RS-T, 17 (3%) with aCML and 52 (10%) with MDS/MPN-U. The median age at diagnosis was 71 (range, 18-99) years, and 333 (66%) were male. TET2MT were seen in 212 (42%) patients, with the frequency of other mutations being: ASXL1 45%, SRSF2 40%, NRAS 15%, SF3B1 13%, CBL, RUNX1 and SETBP1 12% each, and JAK2 V617F 11% (Figure B). Among the MDS/MPN overlap syndromes, TET2 was more frequently mutated in CMML (49%) and aCML (47%) compared to MDS/MPN-RS-T (10%) and MDS/MPN-U (15%). The prevalence of patients with TET2MT increased with age, a finding consistent across all MDS/MPN subtypes (Figure C). Overall, 341 TET2MT were identified in 212 patients (mean 1.6 variants/patient, range 0-5): 120 (24%) had >1 TET2MT, while 113 (22%), 5 (1%) and 2 (0.4%) had 2, 3 and 5 mutations, respectively. CMML and aCML patients were more likely to have an age-independent increase in multiple TET2MT (28% and 24%), in comparison to MDS/MPN-RS-T (4%) and MDS/MPN-U (8%). TET2 MT spanned the entire coding sequence and were mostly truncating (78%, Figure A): 59 (17%) were missense, 14 (4%) involved the splice-donor/acceptor sites, 2 (0.5%) were in-frame deletions, 129 (38%) were nonsense, and 137 (40%) were frameshift mutations. Overall, the distribution of TET2MT was superimposable across CMML, aCML, and MDS/MPN-U; the only exception being the absence of splice site mutations in the latter two. One hundred and eighty-seven (55%) TET2MT were secondary to pathogenic single nucleotide variants (SNV), while the remainders were secondary to deletions (25%) and insertions (15%). Transitions comprised the most frequent type of SNV (65%), with the C:G>T:A being the most common (56%). Patients with MDS/MPN overlap syndrome and TET2MT were more likely to have additional gene mutations compared to wild type patients (mean mutation number 3.1 vs 2.1, p<0.0001), with common co-mutations being SRSF2 (51%), ASXL1 (42%), and CBL (17%). The median overall survival (OS) of the entire cohort was 29 (range, 0-170) months; 29 months for CMML, 63 months for MDS/MPN-RS-T, 14 months for aCML, and 25 months for MDS/MPN-U. On univariate analysis, OS was superior in CMML patients with TET2MT (35 months) compared to wild type cases (21 months, p<0.0001, Figure D), and in CMML patients with >1 TET2MT (41 months) in comparison to wild type (21 months, p<0.0001) and single TET2MT (29 months, p=0.0476) cases (Figure E). These observations were not seen in patients with aCML, MDS/MPN-RS-T, and MDS/MPN-U. Conclusion: Our study demonstrates that TET2MT are among the most frequent mutations in patients with MDS/MPN overlap syndromes (42%), especially CMML (49%), with an age-dependent increase in the frequency and number of TET2MT. Mutations in TET2 were found to span the entire coding sequence, with truncating mutations being more common (78%). Importantly, in CMML, TET2MT, including number of TET2MT, were associated with favorable survival outcomes. Figure Disclosures Al-Kali: Astex Pharmaceuticals, Inc.: Research Funding. Patnaik:Stem Line Pharmaceuticals.: Membership on an entity's Board of Directors or advisory committees.

Introduction: Chronic myelomonocytic leukemia (CMML), an aggressive myeloid malignancy, can be categorized into two subtypes, proliferative CMML (pCMML) and dysplastic (dCMML), based on a white blood cell (WBC) count of ≥ 13 x 109/L for the former (Arber et al. Blood 2016). While this WBC cut off is somewhat arbitrary, patients with pCMML have unique phenotypic features and a shorter survival. We carried out this study to assess the genomic, transcriptomic and epigenetic landscapes of these two CMML subtypes. Methods: Peripheral blood (PB) and bone marrow (BM) mononuclear cells (MNC) were obtained from WHO-defined CMML patients. Next generation sequencing (NGS) using a 36-gene panel was performed on 350 patients with Illumina HiSeq4000 platform with median read depth of 400X. RNA sequencing (RNA-seq) was performed on 25 patients by bulk whole transcriptome sequencing using Illumina TruSeq. DNA immunoprecipitation sequencing (DIP-seq) was performed on 18 patients using 5-methylcystocine (5mC), 5-hydroxymethylcytosine (5hmC) and bridging monoclonal antibodies with subsequent paired-end sequencing using HiSeq4000. Chromatin immunoprecipitation sequencing (ChIP-seq) was performed on 30 patients with Illumina HiSeq2500 to a depth of 25 million for histone 3 lysine 4 monomethylation (H3K4me1) and histone 3 lysine 4 trimethylation (H3K4me3) and 50 million reads for histone 3 lysine 27 trimethylation (H3K27me3) and Input per sample. Results: Five hundred and seventy-three patients with WHO defined CMML were included; median age 71 years (range 18-95 years), 67% males. 282 patients had pCMML (49%), while 291 (51%) had dCMML. As pre-defined, patients with pCMML were more likely to have higher absolute monocyte counts (p<0.0001), circulating immature myeloid cells (p<0.0001), PB blasts (p<0.0001), and higher lactate dehydrogenase levels (p=0.03). At last follow up 234 (41%) deaths and 70 (20%) leukemic transformations were documented. The median OS for pCMML vs dCMML in this cohort was 19 months vs 30 months (p<0.0001, Figure 1A) and validated in an independent Austrian cohort (p=0.02). Genomic profiling: NGS performed on 350 patients (BM MNC) revealed a higher frequency of NRAS (35 vs 17%, p=0.004), cumulative RAS pathway (NRAS, KRAS, CBL and PTPN11) (73 vs 47%, p=0.001), ASXL1 (p=0.003) and JAK2V617F (p=0.04) mutations in pCMML relative to dCMML (Figure 1B); while dCMML had a higher frequency of SF3B1 mutations (p=0.02). There were no differences in distribution of TET2 and SRSF2Transcriptomic analysis: RNA-seq was performed on PB MNC from RAS pathway mutant pCMML patients (n=12) and RAS pathway wildtype dCMML patients (n=13). Unsupervised clustering analysis resulted in appropriate segregation revealing distinct expression profiles between disease subtypes (Figure 1C). Compared to dCMML, 3729 genes were significantly differentially upregulated and 2658 genes were differentially downregulated in pCMML. Among genes most highly upregulated were mitotic checkpoint kinases including AURBK, PLK1, PLK2, PLK4 andEpigenetic profiling: ChIP-seq of PB and BM MNC from pCMML (n=18) and dCMML (n=12) patients and healthy, age-matched controls (n=10) revealed a global increase in H3K4me1, without significant differences in H3K4me3 or H3K27me3 occupancies (regardless of stratification by ASXL1 mutational status; 40% ASXL1mt in pCMML, 30% dCMML) in pCMML vs dCMML (Figure 1D). H3K4me1 occupancy was also increased in a sequence-specific manner at the transcription start sites of the aforementioned mitotic kinases (PLK1 and WEE1). DIP-seq was performed on PB MNC to assess global differences in 5-mC and 5-hmC levels, between pCMML (n=9) and dCMML (n=9), with no differences seen between the two subtypes (regardless of TET2 mutational status, 40% TET2mt in each subtype) (Figure 1E). Conclusions: Despite the somewhat arbitrary WBC distinction between pCMML and dCMML, clear phenotypic, genetic, transcriptomic, epigenetic and survival differences exist between the two subtypes, providing strong biological rationale for this distinction. pCMML patients have a higher frequency of oncogenic RAS pathway mutations, a unique transcriptomic profile enriched in mitotic check point kinases and a unique chromatin configuration with global and sequence specific enrichment in H3K4me1, with no significant global differences in 5mC, 5hmC, or H3K4me3 and H3K27me3 occupancy. Figure 1 Disclosures Geissler: AOP: Honoraria; Pfizer: Honoraria; AstraZeneca: Honoraria; Novartis: Honoraria; Celgene: Honoraria; Roche: Honoraria; Abbvie: Honoraria; Ratiopharm: Honoraria; Amgen: Honoraria. Al-Kali:Astex Pharmaceuticals, Inc.: Research Funding. Patnaik:Stem Line Pharmaceuticals.: Membership on an entity's Board of Directors or advisory committees.

Objective : Central nervous system (CNS) involvement is a known phenomenon of acute lymphoblastic leukemia. However little is known about the incidence of CNS involvement in acute myeloid leukemia (AML) as routine lumbar punctures are not done if patients are asymptomatic at diagnosis. Our practice has been to obtain lumbar puncture (LP) at or after complete remission (CR) for patients that present with any one of the following high risk features;hyperleukocytosis with WBC >10,000 or blastic crisis, extramedullary disease,monocytic differentiation. Methods: We reviewed our leukemia database at Mayo Clinic to determine the incidence of CNS involvement in patients with high risk features after due IRB approval. We also compared baseline demographic characteristics, blood counts, cytogenetic risk groups, presence of extramedullary disease, relapse rate ,transplant rate and overall survival (OS) among patients with and without CNS involvement. OS estimates were calculated by Kaplan-Meier curves and log-rank testing using JMP v.13. Results: 298 patients with AML were identified with presence of at least 1 risk factor for CNS involvement. The results of LP were only available for 126 (42%) patients. The overall incidence of CNS involvement was 12% (15/126, figure 1). Among the patients with positive disease 3 had CSF examination at diagnosis prior to CR due to the presence of CNS myeloid sarcoma (n=2) and ambiguous lineage myeloid leukemia and were excluded from further evaluation. The incidence of CSF involvement at CR1 was 9.7% (12/123). All patient with CNS positive disease received intrathecal chemotherapy with alternating cytarabine and methotrexate until they cleared their blast and additional 2-4 treatments as per treating physician's discretion .The CNS positive and negative patients were compared and did not show any statistical difference in age, gender, presence of extramedullary disease ,cytogenetic risk group, relapse rate and transplant rate as shown in table1. Molecular data was not available in most of the patients and hence was not included for analysis. The median OS was significantly lower among patients with CNS involvement compared to absence of CNS involvement but was not statistically significant likely due to small sample size (3.9 vs12.8 years (p=0.2), figure 2). The overall CNS relapse rate in patients who did not have a LP done at CR was 5.8%(10/172). Conclusions : CNS evaluation should be done in AML patients with high risk features before declaring CR. CNS disease portends overall a poor prognosis with impaired overall survival and high relapse rate. However the sample size was small and true incidence of CNS disease will need routine diagnostic LP in all high risk patients. Disclosures Patnaik: Stem Line Pharmaceuticals.: Membership on an entity's Board of Directors or advisory committees. Al-Kali:Astex Pharmaceuticals, Inc.: Research Funding.

Background Blinatumomab is a bispecific T cell antibody construct, that binds and allows CD-3 positive cytotoxic T cells to recognize and eradicate CD19-positive acute lymphocytic leukemia (ALL) blasts. The drug is approved for patient (pts) with relapsed/ refractory (RR) B-cell ALL and those with minimal residual disease (MRD) based on efficacy in clinical trials. We sought to evaluate the safety and efficacy of blinatumomab in the "real world" setting. Methods We conducted a retrospective multicenter study in collaboration with 11 U.S. academic institutions, and evaluated the outcome of RR B-cell ALL pts, who received blinatumomab outside of clinical trials. These pts were evaluated for response, duration of response (DOR), overall survival (OS) from the time of blinatumomab initiation and toxicity. DOR was estimated among pts who had achieved complete remission (CR)/CR with incomplete count recovery (CRi). Survival curves were estimated using the Kaplan-Meier method and compared via log-rank test. Results From December 2014 to May 2019, 239 pts with B-cell ALL were identified. Baseline characteristics are summarized in Table 1. The median age of pts at blinatumomab initiation was 48 years (yrs) (range, 18-85). Sixty-one (26%) pts had Philadelphia chromosome [t(9;22)] positive (Ph+ve) disease. Sixty-one (26%) pts had ≥ 3 prior therapies and 46 (19%) pts had allogeneic stem cell transplantation (allo-HCT) prior to blinatumomab. Twenty-two (9%) pts received inotuzumab ozagamicin prior to blinatumomab. Twenty-nine (12%) pts received blinatumomab in combination with tyrosine kinase inhibitor (TKI). Twelve (5%) pts received blinatumomab for MRD. Response rate (CR/CRi) in pts with RR disease was 61%; 44% had CR with MRD negativity by flow cytometry. Rate of CR/CRi in Ph+ve B-cell ALL was 74.5%. Among 12 pts who received Blinatumomab for MRD, 9 (75%) pts achieved MRD negativity. Overall 113 (48%) pts were successfully bridged to allo-HCT. Median DOR in pts with RR disease was 32.1 months (95% CI; 9.5-not reached [NR]) (Fig. 1a) and when censored at allo-HCT was 14.8 months (95% CI; 5.2-NR) (Fig. 1b). Median OS in pts with RR disease after blinatumomab was 12.7 months (95% CI; 9.2 -17.9) (Fig. 1c) and when censored at allo-HCT was 8.6 months (95% CI; 6.4-11.6) (Fig.1d). Median OS after blinatumomab in RR B-cell ALL Ph+ve pts was NR (59% alive at 2 yr). Among pts who received blinatumomab for MRD, median DOR was NR and 54% sustained MRD negativity at 2 yrs. Median OS was 34.7 months (95% CI; 8.8-34.7) in group of pts who received blinatumomab for MRD. Seven (3%) pts discontinued blinatumomab due to adverse events and 40 (21%) pts had dose interruptions. Cytokine release syndrome (CRS) of any grade (G) was reported in higher number of pts (93 [39%]) compared to clinical trials, though G3-4 CRS appears to be similar (G1-2 [36%], G3-4 [3%]). Forty-four (44%) pts were treated with steroids and 8 (8%) pts required tocilizumab with steroids for CRS. Ninety-three percent of pts had complete resolution of CRS. CNS toxicities were observed in 31 (13%) pts, among them 60% (n= 19) had G3-4 toxicities. Hepatic toxicities were observed in 84 (35%) pts as outlined in Table 1. Six (2.5%) pts died due to blinatumomab induced toxicities. Conclusion: Our real-world data with multicenter collaboration suggest that overall blinatumomab was well tolerated and had led to significant response in pts with RR B-cell ALL. Disclosures Advani: Amgen: Research Funding; Abbvie: Research Funding; Pfizer: Honoraria, Research Funding; Macrogenics: Research Funding; Kite Pharmaceuticals: Consultancy; Glycomimetics: Consultancy, Research Funding. Aldoss:AUTO1: Consultancy; Helocyte: Consultancy, Honoraria, Other: travel/accommodation/expenses; Agios: Consultancy, Honoraria; Jazz Pharmaceuticals: Honoraria, Other: travel/accommodation/expenses, Speakers Bureau. Podoltsev:Agios Pharmaceuticals: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Blueprint Medicines: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Boehringer Ingelheim: Research Funding; Astellas Pharma: Research Funding; Alexion: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Research Funding; Sunesis Pharmaceuticals: Research Funding; Jazz Pharmaceuticals: Research Funding; Pfizer: Research Funding; Astex Pharmaceuticals: Research Funding; CTI Biopharma: Research Funding; Celgene: Other: Grant funding, Research Funding; Genentech: Research Funding; AI Therapeutics: Research Funding; Samus Therapeutics: Research Funding; Arog Pharmaceuticals: Research Funding; Kartos Therapeutics: Research Funding. Curran:Incyte: Research Funding; Merck: Research Funding; Gilead: Research Funding. Yang:Agios: Consultancy; AstraZeneca: Research Funding. Mattison:Pfizer: Membership on an entity's Board of Directors or advisory committees. Liedtke:Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; IQVIA/Jazz: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech/Roche: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celator: Research Funding; Caelum: Membership on an entity's Board of Directors or advisory committees; BlueBirdBio: Research Funding; Amgen/Onyx: Consultancy, Honoraria, Research Funding; Adaptive: Membership on an entity's Board of Directors or advisory committees; Agios: Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Prothena: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Atallah:Helsinn: Consultancy; Takeda: Consultancy, Research Funding; Jazz: Consultancy; Pfizer: Consultancy; Helsinn: Consultancy; Novartis: Consultancy; Jazz: Consultancy.

Introduction: Short telomere syndromes (STS) are accelerated aging syndromes affecting hematopoietic, pulmonary, hepatobiliary and/or immunological systems. Clinical assessment of age-appropriate telomere length (TL) is performed using flow cytometry & fluorescence in-situ hybridization (flowFISH). Screening for germline variants in STS-related genes is guided by flowFISH-determined centile categories of TL, with screening recommended for TL <1st centile or 1-10th centile in lymphocytes (L) or granulocytes (G). However, the utility of genetic testing for patients with TL >10th centile and integration of clinical phenotype with flowFISH data in predictive algorithms is currently unclear. Methods: FlowFISH testing was done at reference laboratories in Vancouver (Repeat Diagnostics; Canada) & Johns Hopkins University (JHU, USA). Salient clinical features were pre-determined as, personal history of premature hair greying (onset at age < 30 years), idiopathic pulmonary fibrosis (IPF) or IPF/emphysema overlap (in smokers), cryptogenic cirrhosis or NRH, unexplained cytopenias &/or immunodeficiency, & family history of the above (in >1 1st or 2nd degree relatives). Clinical likelihood score (CLS) was assigned as low (1), intermediate (int, 2) or high (>2), based on the number of aforementioned clinical features present prior to flowFISH testing. Genetic testing was performed using either an in-house or commercial bone marrow failure-specific next generation sequencing (NGS) panel or whole exome sequencing (WES), and data for known variants affecting telomerase or telomeric function (TERT, TERC, DKC1, TINF2, NHP2, NOP10, TCAB1, NAF1, & RTEL1) was recorded. Results: One hundred forty-nine patients at our institution underwent TL assessment at Repeat diagnostics (n=38) and JHU (n=111) laboratories, respectively. Median age was 56 (range: 7-79) years; 88 (59%) being males. Significant family history was present in 40 (27%) patients, while premature greying of hair was present in 13 (9%) patients. Organ-specific clinical features included unexplained cytopenias (n=89, 60%) IPF (n=71, 48%), cryptogenic cirrhosis or NRH (n=21, 14%), & unexplained immunodeficiency (n=14, 9%). CLS stratification included low (n=74, 50%), int (n=54, 36%), & high (n=21, 14%), with higher CLS significantly correlating with lower delta TL for L (p=0.0005) but not G (p=0.3). Genetic testing was performed in 51 (35%) patients (NGS-51, WES-1) among which 13 (26%) patients had a telomere-associated variant; 5 (10%) pathogenic (pv, all TERT). CLS alone was unable to predict likelihood of finding a telomere-associated variant (p=0.4). Based on age-appropriate centile categorization of L & G TL (information for both available in 134 patients), patients were stratified into six groups (table 1). TL <1st centile in L: This group was further divided into two groups; TL<1st centile in both L & G [A1, n=7, CLS low-3 (43%), int-2 (29%), & high-2 (29%)] and TL <1st centile in L and 1-50th centile in G (A2, n=2, CLS low & high) patients. Among the 4 (57%) patients who underwent genetic (NGS-3, WES-1) testing, 3 (75%) had TERTpv in A1 subgroup and 1 A2 subgroup patient had a VUS in TERT.TL <1st centile in G, 1-10th centile in L (n=18): This group included 9 (50%) low, 8 (44%) int and 1 (6) high CLS patients, of which only 1 of 8 NGS-tested patients had TERTpv.TL 1-10th centile in L or G: This group was divided into; 1-10th centile in both L & G [C1, n=28, CLS low-3 (11%), int-14 (50%), high-11(39%)] of whom 8 (22%) underwent NGS with no pathogenic variants but 3 VUS in RTEL1, NAF1 & PARN genes, and 1-10th centile in L, >1-90th centile in G [C2, n=36, CLS low-19 (53%), 16 (44%), 1 (3%)] of whom 8 (22%) underwent NGS with 1 TERTpv and 2 VUS in TINF2TL >10th centile in L & 1-90th centile in G (n=43, 32%): CLS stratification in this group included 27 (63%) low, 12 (28%) int, 4 (9%) high. NGS testing was done in 13 (30%) patients [CLS low-9(69%), int 2(15%), high 2 (15%)], of whom only 2 (15%) had VUS in TINF2 and TERT gene, but no pathogenic variants (figure 1). Conclusion: Our study demonstrates the importance of using a flowFISH assay based predictive algorithm to screen patients with suspected STS for telomere-related genetic alternations, in comparison to a clinical likelihood score. We also demonstrate a limited role for genetic testing in patients with lymphocyte TL >10th centile, regardless of the clinical likelihood score. Disclosures Patnaik: Stem Line Pharmaceuticals.: Membership on an entity's Board of Directors or advisory committees.

Background MDS is a heterogeneous disease and the revised International Prognostic Scoring System (IPSS-R) is utilized in prognostication. The percentage (%) of blasts in the bone marrow is determined in the aspirate morphologically. Though the former is the standard of care the blast percentage is also reported by flow cytometry and biopsy which can many times be inconsistent. We previously presented the utilization of biopsy based blast percentage which showed meaningful prognostic groups compared to aspirate. In this study we compare the blasts as reported by the aspirate and flow cytometry in MDS-EB in calculating IPSS-R. Methods The MDS database was reviewed for cases of MDS-EB after due IRB approval at the Mayo clinic. We calculated IPSS-R scores based on the aspirate blast % (IPSS-RAsp) and flow blast% (IPSS-Rfl). The aspirate blast percentage was reported morphologically. Suboptimal aspirates were excluded from the study. The flow blast percentage was determined by immunophenotyping. The overall survival (OS) was determined by IPSS-RAsp and IPSS-RFl. OS estimates were calculated by Kaplan-Meier curves and log-rank testing using JMP v.13. Uno's concordance statistic was used to compare the 2 risk scoring systems. Results Of 1322 patients, 431 (33%) cases were identified with MDS-EB out of which 120 (29%) cases had blasts reported in the aspirate and flow. Based on aspirate MDS EB1: 54% (n=65), MDS EB2 46% (n=55). The hematological, cytogenetic and R-IPSS categories were compared between MDS-EB1 and MDS- EB 2. The blast percentage and hemoglobin levels was significantly different between MDS-EB1 and EB2 as seen in table 1, however the IPSS-R risk groups were not significantly different. The flow cytometry was concordant with aspirate in 66/120 (55%) cases. Out of the dis-concordant cases only 20% (11/54) was upstaged by flow cytometry with most of the patients being down staged as expected by the techniques used in processing the blood and hence not reliable when reported low (Figure 1). The OS outcomes based on the IPSS- R asp, IPSS-Rfl areshown in figure 2A,2B .The p value with aspirate based R-IPSS was more significant than flow cytometry based R-IPSS (p= 0.0007 vs 0.0174). We compared the two models for observed OS differences using the Uno model which was not statistically significant. (p= 0.6) Conclusions Both models did not show a difference which is likely due to the very small sample size. However flow cytometry did down stage more patients when disconcordant and may have less value in that setting. It would be ideal to compare all 3 models aspirate, biopsy and flow cytometry however we did not have enough number of patients to do the comparison. Disclosures Patnaik: Stem Line Pharmaceuticals.: Membership on an entity's Board of Directors or advisory committees. Al-Kali:Astex Pharmaceuticals, Inc.: Research Funding.