ALBERT

Description: Lenalidomide (LEN) has established a new paradigm of targeted therapy in MDS. The mechanistic underpinnings of LEN efficacy are related to the synthetic lethality of this agent through its ability to bind cereblon (CRBN). LEN induces degradation of CK1α, which is encoded by the CSNK1A1 gene located on the del(5q) CDR, whereby haploinsufficient levels of this gene allow for selective toxicity to deletion mutants. Another common cytogenetic abnormality present in patients with myeloid neoplasia (MN) is -7/del(7q). To date no selective therapies exist for -7/del(7q), an urgent unfulfilled need, given the poor prognosis associated with this cytogenetic abnormality. We were interested to explore if this same notion of selective toxicity may be possible in del(7q) myeloid patients and sought to screen drugs for this focused population. From a large cohort of patients with MN (n=3,328), we found -7/del(7q) in 10% (n=316) of patients. We first identified a signature pattern of haploinsufficient genes on -7/del(7q) based on NGS. We then searched for haploinsufficient genes which, if targeted by investigational drugs, could provide a therapeutic window for selected MN subtypes in analogy to LEN in del(5q). For the purpose of our analysis, haploinsufficient expression was defined as

Description: Large granular lymphocytic leukemia (LGLL) is an indolent disease and often associated with autoimmune disorders such as rheumatoid arthritis. The association of humoral immune disorders resulting from abnormal B cell activity, may affect original LGLL pathogenesis, clinical presentation and management through modifying disease presentation, progression and/ or resistance to standard care. Coexistence of T cell LGL leukemia with B cell abnormalities has previously been identified in the literature although described in sporadic case reports. However, no large case series or cohorts have been collected so far to study the frequency of the B-cell dyscrasia (BCD) associated with LGLL and describe clinical/ hematological findings in patients with this co-association. Here, we conducted a retrospective review of patients diagnosed with LGL leukemia at The Cleveland Clinic Foundation to search for any associated BCDs. We then classified our population into 2 groups: LGLL with BCD vs. LGLL without BCD, and comprehensively compared them for baseline, clinical and molecular characteristics. A total of 244 T-LGL patients were collected and studied. All cases were uniformly diagnosed with LGLL if 3 out of 4 following criteria were fulfilled, including: 1) LGL count 〉500/µL in blood for more than 6 months; 2) presence of abnormal CTLs expressing CD3, CD8 and CD57 by flow cytometry; 3) preferential usage of a TCR Vβ family by flow cytometry; 4) TCR gene rearrangement by PCR. Molecular studies including targeted deep sequencing for STAT3mutations were performed. Bone marrow biopsy results were reviewed to exclude other conditions. Endpoints of the study were death or lost to follow up. In our cohort, we found a frequent manifestation of humoral immune system abnormalities. We identified coexisting BCD in 45% (109/ 244) of LGLL patients, of whom 28 (11.2%) had monoclonal gammopathy of unknown significance (MGUS), and 13 (5.2%) had chronic lymphocytic leukemia (CLL/SLL). Six LGLL patients had multiple myeloma (2.4%). Moreover, polyclonal hypergammaglobulinemia (n=28, 11.2%) or hypogammaglobulinemia (n=14, 5.6%) was reported in 42 LGLL-patients (16.8%). The frequency of other disorders of B-cell origin was also examined. The total incidence of B-cell abnormalities in our LGLL cohort was 45%. Indeed an heterogeneous appearance of other B-cell disorders was observed including mantle cell lymphoma (n=2), DLBCL (n=6), marginal zone lymphoma (n=3), Waldenstrom's macroglobulinemia (n=1), Burkitt's lymphoma (n=1), indolent lymphoma (n=1), Hodgkin's lymphoma (n=1), non-Hodgkin's lymphoma (n=3), neck lymphoma (n=1), and smoldering myeloma (n=2). Patient with LGLL-BCD were older as compared to the ones without (median age: 62 vs. 63 years; ≥60 years: 57% vs. 69%, respectively), although the difference was not statistically significant (P=0.07). Gender was equally distributed (male: 54%, n=132; female: 46%, n=112) in patients who developed BCD. Conventional cytogenetics showed that patients without BCD were more often associated with abnormal cytogenetics (24%, n=9) as compared to LGLL-BCD (9%, n=5). Interestingly, BCD was found in 55 men and 54 women in whom only 6 patients had NK-LGLL while the remaining (n=103 patients) had T-LGLL suggesting a higher association with LGLL of T- rather than of NK-cell origin. Leukopenia was observed in 25/109 patients, with average absolute lymphocytes of 4.18 k/µL and LGL count of 2333 k/µL. Blood count showed: neutropenia in 44, anemia in 65, and thrombocytopenia in 29 out of 109 LGLL patients with BCD. TCR rearrangements were seen in 74 while somatic STAT3 mutations were observed in 37 LGLL patients while more enriched (44%, n=52) in LGLL without BCD. The association of other autoimmune conditions e.g., rheumatoid arthritis, was not different between the two groups (15% vs. 16% in LGLL with BCD vs. without; P=0.8). In sum, our investigation shows that BCD were frequent in LGLL and coexisted in 45% of the patients, commonly in the form of MGUS, and/ or hypergamaglobulinemia. Perhaps, the co-association of B-cell pathology with LGLL suggests that the two diseases either share pathogenetic driving mechanisms to enhance both B cells and T cells clones or that immunological dysfunction in setting of B cell dyscrasia could trigger/potentiate LGL expansion and/or transformation in this context. Disclosures No relevant conflicts of interest to declare.

Description: Genetic studies have been early introduced for the classification of acute myeloid leukemia (AML), but specific molecular lesions [e.g., t(8;21), inv(16), t(15;17)] define only a fraction of patients. In the genomic era, many mutations and cytogenetic abnormalities and their combinations have been described in AML; their diversity contributes to the heterogeneity of pathomorphologic presentations. While certain mutations are restricted to individual classical morphologic subtypes, pathognomonic lesions are difficult to find. Therefore, to date, molecular mutations or cytogenetic abnormalities have been used to assess prognosis rather than define disease sub-entities according to molecular pathogenesis, likely a future standard in AML diagnosis. Balanced translocations are prototypic founder lesions, however, founder somatic vs. subclonal mutations have not been used to define subtypes of AML. Molecular classification may better reflect the pathogenesis of AML than morphologic/clinical subtypes e.g., secondary (sAML) vs. primary AML (pAML) or AML with normal (ncAML) vs. abnormal cytogenetics (acAML). This work describes the results of a large and comprehensive analysis of genomic landscape and cytogenetics in AML. Initially, 6788 cases were analyzed, including 4867 from our institutions (Cleveland Clinic Foundation and Munich Leukemia Laboratory, n=4862) fortified by publically deposited cases (n=1926) to define gene signatures and succession of mutations distinguishing pAML vs. sAML. While data for core-binding factor AML, MLL gene rearrangement leukemia, acute promyelocytic leukemia and therapy-related AML have also been analyzed (n=1094), we focused on remaining sAML (n=876) vs. pAML (n=4808) and within these entities (ncsAML, n=367; acsAML, n=509 vs. ncpAML, n=2856 and acpAML, n=1952). Although, sAML and pAML showed usual clinical differences, a reliable diagnostic algorithm could not be constructed using supervised analytic approaches and thus we aimed at identification of molecular biomarkers with prognostic and diagnostic value. Abnormal cytogenetics were present in 57% of AML including complex: 13%, +8; 11%: -5/del(5q): 8%; and -7del7q: 8%. Deep NGS for the 25 top mutated genes was applied and correlated with clinical and cytogenetic parameters (Fig.1A-B). We then defined/compared mutational landscape in acAML and ncAML separately. AcsAML showed more complex karyotypes (58% vs. 40% in acpAML, P

Description: Acute promyelocytic leukemia (APL) is characterized by PML-RARA fusion caused by the t(15;17)(q24;q21) translocation. Although PML-RARA fusion explains the dedifferentiation in most of APL patients, it still does not entirely represent the unique cause of all the clinical manifestations of the disease failing to determine the full leukemic phenotype. Up to 40 % of APL patients have an additional chromosomal abnormality other than PML-RARA. Murine studies have reported that additional cytogenetic abnormalities and secondary somatic mutations (for instance FLT3-ITD) might contribute to leukemia progression. Indeed, mice expressing mutant PML-RARA develop definitive leukemia after one year, suggesting that additional hits are required for transformation. Moreover, no distinct genetic signature has been characterized by next generation sequencing (NGS). This confirms that no gene has been reproducibly identified. APL respond to all-trans retinoic acid (ATRA) in the great majority of patients. However, one quarter of APL develop ATRA resistance suggesting that additional secondary chromosomal abnormalities might be evolving resistance. Combination of low dose arsenic, modify certain epigenetics, with ATRA decreased resistance potential and improved response. In the line with other possible factors involved in ATRA resistance, is the broad nature of the targets of ATRA. A molecular core network of ATRA's targets has been clustered in differentiation, growth factors and nuclear receptors possibly cooperating with PML-RARA and additional chromosomal abnormalities. Herein, we aimed to characterize the gene mutations and chromosomal abnormalities playing key roles in cellular differentiation and epigenetic regulation and to correlate the occurrence of these alterations with treatment response and survival outcomes in APL. We took advantage of a large cohort of APL patients (n=145). Median age of the cohort was 50 yrs (19-85); equal gender distribution; median blood counts were: [WBC 6.2 x 109/L (0.4-155); 37% had leukopenia], hemoglobin [9.8 g/dL (2.7-16.2); 32% had anemia] and platelets [29 x 109/L (range of 0-228); 93% had thrombocytopenia]. In terms of karyotype, 15% of the patients carried +8, 7% had complex karyotyping (≥3 cytogenetic abnormalities), 2% had -7/del (7q) or del (12p), 1% had -17/del(17p), and 1 patient had -5. Mutational analysis of 30 genes panel, identified 141 mutations carried by 65% (94/145) of APL patients. The most frequent mutations were observed in FLT3-ITD (61/143; 43%), WT1 (26/139; 23%), and ASXL1 (7/136; 5%) genes. Less frequent mutations were found in 3.7% of CEBPA, KRAS, and NRAS genes as well as in CBL, EZH2, TET2 (3% each) genes. Additionally, we noted that all mutations were recurrent in specific functional pathways and patients carried mutations in more than 1 gene of the same pathway. Of note, cell signaling and proliferation genes (CBL, NRAS, KRAS, KIT, FLT3) were the most frequently mutated (77/141, 55%) and impacted OS (HR: 1.7, P=0.02). Moreover, transcriptional factors which are often mutated in AML (e.g. CEBPA, TP53, NPM1, RUNX1, WT1) as well as major determinants of cell's fate were markedly mutated (38/141, 27%) suggesting that genetic impairment of signaling and transcription might contribute to the lack of differentiation observed in APL phenotypes. Mutations in epigenetic genes and histone methyltransferases (ASXL1, BCORs, DNMT3A, EZH2, IDH1/2, TET2) were also found in 18/141 (13%) while genes regulating cell proliferation and RAS family (CBL, NRAS, KRAS, NPM1) were enriched in 16/132 (12%) of APL cohort. We then analyzed the genetic picture of remission (APLRm, n=131, 90%) and relapsed (APLR, 1sr relapsed to ATRA, n=14, 10%) patients. Acknowledging the low number of APLR, we observed that molecular mutations did not make a key difference in APLRvs. APLRm [except for a complete lack of mutations in epigenetic pathways (0% vs. 13%)]. Contrarily, specific cytogenetic abnormalities were more common in APLR compared to APLRm as the case of +8 (36% vs. 11%; P= .02) and -17/del(17p) (2/14 vs. 0/131; P= .008). In sum, our study demonstrates that PML-RARA might be accompanied by additional acquired chromosomal change with a variety of genetic mutations in key pathways driving cellular differentiation. These molecular/ cytogenetic associations could determine resistance to ATRA and overall APL patients' survival. Disclosures No relevant conflicts of interest to declare.

Description: Mutations (MT) in the 5' untranslated region (UTR) of ANKRD26 (A26) are implicated in ANKRD26- related thrombocytopenia (A26-RT), an autosomal dominant disorder of mild to moderate thrombocytopenia (TP) often presenting in adulthood, although severe and pediatric cases are reported. Erythrocyte and leukocyte counts are normal to increased, with unremarkable morphology. Platelet (plt) size is usually normal, as with ETV6- and RUNX1-mutated TP. Together, A26, ETV6, and RUNX1 germline (GL) MT comprise a separate 2016 WHO category of myeloid neoplasms (MN) with GL predisposition and preexisting platelet disorders. Normal plt size separates A26-RT from other familial TPs with giant plts. No consistent morphological plt aberrations have been reported. Bleeding history is absent or mild, and while TP is not life threating, 8-10% of patients (pts) develop a MN, including a 30-fold increased risk for AML relative to the general population. A26 is an inner membrane adaptor protein with 2 major domains: ankyrin repeats (ANKR) and coil-coil (C-C), both of which interact with signaling and cytoskeletal proteins. A26-RT MT are almost exclusively in the 5'UTR, however, rare A26 coding variants (A26-CV) are reported to segregate with familial TP. Still, some studies on A26-RT limit sequencing to the 5'UTR. As such, A26-CV are not well represented or described. We performed whole-exome sequencing (WES) on 195 pts with MN seen at Cleveland Clinic between 2004 and 2012, and downloaded WES .bam files from online sources, totaling 653 MN cases. Using a standard pipeline for discovery of rare GL variants (

Description: Therapy-related acute myeloid leukemia (t-AML) is a complex disease entity. It results from molecular abnormalities induced by chemotherapy, radiation and immunosuppressive therapies. As a group of diseases, t-AML may represent cases that progressed from therapy-related myelodysplastic syndromes (t-MDS) and "de novo" t-AML. The classification t-AML also includes patients (pts) whose AML is a second primary cancer e.g., due to a genetic predisposition to develop multiple, distinct cancers (those cases would be indistinguishable from the non-therapy-related AML). Origins of the disease may also vary: t-AML may evolve from clonal hematopoiesis of indeterminate potential (CHIP) that preceded the first cancer, as a de novo disease or as a disease which progressed from "de novo" CHIP. Comprehensive genomic analyses involving clonal hierarchy may reveal genetic patterns pointing towards a potential molecular pathogenesis. We applied targeted gene sequencing to analyze a large cohort of pts with AML (n=2696) for the presence of somatic mutations: comparator subtypes include primary AML (pAML, n=2133) and secondary AML (evolving from an antecendent MDS; sAML, n=446) to be compared to t-AML (n=117). These pts have had a history of other primary malignancies for which they received cytotoxic treatments including chemotherapy and/or radiation. t-AML pts were younger than pts with other AML types (median age: 60 years for t-AML vs. 65 and 69 for pAML and sAML). t-AML pts were more likely to have leukopenia compared to pAML (23% vs. 21%, P=0.7) but significantly less likely than pts with sAML (23% vs. 38% P=0.002). Normal cytogenetics were significantly less present in t-AML when compared to pAML (39% vs. 62% P

Description: Chromosomal abnormalities can be founder lesions (e.g., t (8; 21), inv (16), inv (3)), initiate or advance disease progression (both founder and secondary hits e.g., ASXL1, TP53, RUNX1) or can be obligatory secondary hits (FLT3, NPM1). Hence, the rank of these mutations may determine the biological properties and clinical outcomes. However, while many mechanistic studies have been undertaken without identifying the key pathogenetic factors resulting from SF3B1 mutations, important biological clues can be derived from the consequences of SF3B1 alterations in the context of the clonal architecture of myeloid neoplasia (MN). SF3B1 mutant patients often have a homogeneous phenotype with isolated erythroid dysplasia, ring sideroblasts (RS) and favorable prognoses. Studies in primary MDS cells have suggested that SF3B1 mutations are initiating lesions and provide a marked clonal advantage to MDS-RS cells by propagating from rare lympho-myeloid hematopoietic stem cells. However, there is significant diversity of clinical phenotypes and outcomes including the observation that the disappearance of RS can be observed during the disease course of clonal MN and might suggest cellular shifts due to acquisition of additional hits. In such scenarios, the cell's fate in the context of SF3B1 mutations is pre-defined by the predominance of expanded hits. We took advantage of our detailed database of molecularly and clinical annotated cases with MN to study the SF3B1 mutatome and describe whether the clonal nature (ancestral vs. secondary) might change the clinical and phenotypic trajectories of MDS cells and whether the concatenation of mutations decreases the competitiveness of SF3B1 clones, leading to the dominance of other driver genes and subsequently to clonal evolution. The clonal hierarchy was resolved using our in-house designed VAF-based bioanalytic method and confirmed by the PyClone pipeline, which showed a high level of concordance. We first assigned clonal hierarchy to SF3B1 mutations by using VAFs (adjusted for copy number and zygosity) and classifying the mutations into dominant (if a cutoff of at least 5% difference between VAFs existed), secondary (any subsequent sub-clonal hit) and co-dominant hits (if the difference of VAFs between two mutations was

Description: Rationale: Dose-reduction of a nucleoside analog reduces cytotoxicity and hence can increase safety, but with less cytotoxicity-driven efficacy as a trade-off. Such an efficacy trade-off, however, may not apply to the nucleoside analog decitabine, because it has a molecular-targeted action of depleting DNA methyltransferase 1 (DNMT1) separable from cytotoxicity, and that occurs and is saturated at low concentrations. In fact, higher decitabine doses/concentrations, by causing cytotoxicity, limit feasible exposure times for this molecular effect that can cytoreduce p53-null, chemorefractory myeloid malignancies via terminal-differentiation instead of apoptosis, simultaneously sparing normal hematopoiesis. Hence, we designed decitabine application to avoid cytotoxicity and increase DNMT1-targeting and describe here results in 69 patients (25 of whom were previously described with shorter follow-up (NCT01165996)(J Clin Invest 2015; 125(3):1043-55]). Methods: IRB approved Myeloid Malignancy Registry (16-020) and Sample Repository protocols (5024) curated demographic, laboratory, intervention, outcome, and mutational data in myeloid malignancy patients after written informed consent; 69 of 1694 patients in the Registry received the alternative decitabine regimen: (i) Dose: 0.1-0.2 mg/kg (~3.5-5 mg/m2), verified to deplete DNMT1 without cytotoxicity in primate and human studies; (ii) Schedule: 1-2X/week, frequent and distributed, to increase S-phase dependent DNMT1-depletion; (iii) Route: subcutaneous, to avoid high peak concentrations.A standard starting dose of 0.2 mg/kg was reduced to 0.15 mg/kg if infection risk was high (e.g., ANC10% or for lack of response to 1X/week. Neutropenia from treatment was managed by interruption then resumption upon neutrophil recovery (same dose or lower by 0.05 mg/kg). Routine anti-emetic prophylaxis was not required. Results: Non-cytotoxic DNMT1-depletion was confirmed by bone marrow gH2AX and DNMT1 measurements (published for 1st25 patients). The 69 patients had MDS 54%, MDS/MPN 14%, MPN 17% and AML 15%. Their median age was 69 years (range 45-89). Prior therapies (77%) were 5-azacytidine 29%, lenalidomide 19%, erythropoietin 26%, hydroxyurea 7%, ruxolitinib 7%, cytarabine 4%. The side-effect was neutropenia (non-cytotoxic DNMT1-depletion skews myeloid differentiation away from GMP and to EMK), complicated by fever/infection in 31 patients (45%), with 1 septic death. Eight of these 31 patients (25%) had fever/infection before treatment. Blood count improvements meeting IWG criteria for response (hematologic improvement [HI]/complete remission [CR]) occurred in 30 patients (43%; CR 14%) (Fig 1A) and were durable(median treatment duration in HI/CR 82 weeks [range 14-347]). Treatment decreased bone marrow myeloblasts, even in cases without HI/CR (Fig 1B). HI/CR was achieved in MDS/AML containing monosomy 7, trisomy 8, complex cytogenetic abnormalities and/or multiple mutations (Fig 1C). Cytogenetics were normalized in 10/36 (28%) (Fig 1C). Patients with HI/CR had better overall survival (median 31 vs18 months) (p=0.036) (Fig 1D). Predictors of HI/CR were higher baseline neutrophils (median 3.04 vs 1.23 x109/L; p=0.002)and higher marrow cellularity (median 70 vs48%; p=0.044)(Fig 1E, F). Conclusion: Myeloid malignancies containing diverse genetic abnormalities responded sustainably (up to 6.5 years follow-up) to a decitabine regimen designed and demonstrated to be non-cytotoxic yet DNMT1-targeting, consistent with scientific data validating DNMT1 as a mutation-agnostic target that operates in a final common pathway of myeloid transformation. Although this single-agent regimen is non-curative, we postulate that avoidance of cytotoxicity, combined with target-validity, enabled sustained disease control/transfusion-freedom in several patients. Reported links between some mutations, e.g., in TET2, and decitabine response could be via higher neutrophils that in turn enable frequent decitabine exposures, a basic requirement for response. Also fundamental, HI/CR requires not just suppression of malignant clones but marrow capacity to support and recover functional hematopoiesis, suggesting why low baseline marrow cellularity predicted non-response. Disclosures Maciejewski: Novartis: Consultancy; Alexion: Consultancy. Saunthararajah:Novo Nordisk: Consultancy; EpiDestiny: Consultancy, Equity Ownership, Patents & Royalties. OffLabel Disclosure: Alternative dose and scheduling of Decitabine for myeloid neoplasms

Description: Acute myeloid leukemia (AML) with t(8;21) or inv(16) chromosomal rearrangements are distinct heterogeneous disease entities within AML that are classified together as core binding factor AML (CBF-AML). Given the nature of the chromosomes involved, these rearrangements lead to the production of leukemogenic chimeric transcripts (RUNX1-RUNX1T1 and CBFB-MYH11) which disrupt the physiologic activity of the heterodimeric transcription factor CBF complex. Although CBF-AML patients have a favorable prognosis and good response to treatment compared to other AML subtypes, survival outcomes are not uniform. Indeed, 30-50% of patients with CBF-AML eventually relapse, and the 5-10 yr survival ranges between 55-61% for patients 〈 60 yr in MRC/NCRI AML trials. Studies have analyzed the clonal architecture of CBF-AML patients and identified cooperating mutations independently of receptor tyrosine kinases (FLT3, KIT) mutations while others have found a 30% occurrence of KIT mutations. Studies of murine models of Runx1 and Cbfb have demonstrated that inactivation of both genes does not lead to leukemia, suggesting that other factors are necessary to recapitulate the leukemia phenotype fully. Although mutations in RAS family of genes (NRAS/KRAS) are among the most frequently observed mutations described in CBF-AML [54% in inv(16) and 30% in t(8;21)], no associations between those mutations and survival outcomes have been found. Because of the lack of association between RASMT and clinical outcomes, their role in CBF-AML is still unknown. Here, we focused on dissecting the impact of RAS mutations (NRAS/KRAS; RASMT) on the clinical characteristics, survival outcomes, and the molecular associations among CBF-AML patients by evaluating the clonal succession of RASMT. In total, 284 CBF-AML patients were identified, in whom inv(16) and t(8;21) represent 61% (n=173) and 39% (n=111) of the cases, respectively. Thirty-five % (99/284) of the patients carried RAS mutations (NRAS=78; KRAS=21) with 8 patients harboring 2 mutations comprising NRAS, KRAS, or both NRAS/KRAS genes. RAS mutations were point mutations affecting known hotspots in NRAS and KRAS. Both RASMT and RASWT had a median age 〈 60 years (55 (14-83) vs. 49 (7-83) years, P=0.9) and sex was equally distributed among the two groups. Leukopenia, defined as white blood cell count

Description: Large granular lymphocytic leukemia (LGL) is a lymphoproliferative cytotoxic T cell (CTL) that typically presents in elderly population. The spectrum of the disease ranges from semi-reactive oligoclonal to clonal CTL expansion, and from silent to a chronic leukemia with para-neoplastic manifestation. However the description of the disease still preceded the new genetic landscape mapping techniques. In lieu of this, we analyzed the genetic landscape of LGL using a set of 33 genes. Interestingly, not only did the deeper analysis help with a better understanding of the complex CTL proliferative processes but indicated a suspected association with conditions such as clonal hematopoiesis of indeterminate potential (CHIP). Association of LGL with age related CH has been described in the past by us and others. Our results indicate that LGL is often associated with the presence of myeloid mutations, generally consistent with the most common typical CHIP mutations (DNMT3A, TET2, ASXL1). We then analyzed a set of 13 patients with coexistent MDS/LGL. This observation raises the question that LGL is, at least in some cases, a tumor surveillance response. All LGL patients were diagnosed using a stringent single center diagnostic criteria and at the time of diagnosis, were also checked for other conditions including MDS to prevent any risks of overlooked diagnoses. A previously well described diagnostic standard of 〉3/5 positive criteria was used; (i) presence of large granular lymphocytes (〉500/μL, by differential counts from complete blood count) for 〉6 months; (ii) abnormal cytotoxic T lymphocytes expressing CD2, CD56 and CD57 and lacking CD28; (iii) preferential usage of a TCR Vβ family by flow cytometry; and (iv) TCR gene rearrangement by PCR; (v) bone marrow infiltration with LGL is another diagnostic criterion but a designated marrow biopsy is often not performed in clear LGL which are otherwise asymptomatic. Coexistent presence of MDS and LGL was confirmed in 13/240 (5%) of the patients. These patients displayed typical features of MDS including abnormal cytogenetics (8/13), dysmorphia of myeloid cells in the bone marrow (13/13), ringed sideroblasts (1/13) and the presence of highly clonal somatic myeloid mutations (8/13) with an average VAF of 28+3%. When compared to LGL only, the MDS/LGL series had 15% vs. 39% (P=0.014) STAT3/5b mutations. We detected the presence of mutant myeloid clones in 25% (41/161) of the patients with pure LGL with an average VAF of 35+ 2%. Suspecting that these mutations may be present early in MDS and CHIP, we compared the mutational spectrum of LGL against MDS (n=835) and CHIP. Indeed, an overlap between the typical CHIP mutations was noted with LGL; in addition the clonal burden in CHIP was observed to be lower, 13% vs. 33% in LGL indicating a more advanced myeloid disease in LGL. This could be due to overlapping demographics or through a common pathophysiologic link. Spliceosomal mutations, cohesion complex, PRC2 and RAS mutations were overrepresented in MDS and CHIP in comparison to LGL. Our results indicate that LGL is often associated with myeloid mutations that are also typical in CHIP. Though, age-related changes or other mutagenic stressors, including inflammatory changes could be contributing factors to both LGL and CHIP outgrowth, conversely LGL may evolve as a consequence of a tumor surveillance response to myeloid neoplasms or CHIP. While the coexistence of MDS and LGL has been described in the past, and our analysis corroborates this, we observed that LGL may also coexist with CHIP in some patients. The implication of this would be beneficial to our understanding of, not only, the individual diseases but could also impact care in CHIP survivorship. Disclosures Nazha: MEI: Other: Data monitoring Committee; Novartis: Speakers Bureau; Jazz Pharmacutical: Research Funding; Incyte: Speakers Bureau; Tolero, Karyopharma: Honoraria; Daiichi Sankyo: Consultancy; Abbvie: Consultancy. Saunthararajah:EpiDestiny: Consultancy, Equity Ownership, Patents & Royalties; Novo Nordisk: Consultancy. Sekeres:Celgene: Membership on an entity's Board of Directors or advisory committees; Millenium: Membership on an entity's Board of Directors or advisory committees; Syros: Membership on an entity's Board of Directors or advisory committees. Maciejewski:Novartis: Consultancy; Alexion: Consultancy.