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Germline mutations in the shelterin component protection of telomeres 1 (POT1) were recently found to be associated with familial chronic lymphocytic leukemia (CLL), melanoma, glioma, and several other familial cancer syndromes. The role of POT1 mutations in myeloid neoplasms and other hematologic malignancies, however, remains unknown. To explore the role of POT1 variants in hematologic neoplasms, we analyzed POT1 variants in 3323 consecutive patients who underwent next-generation sequencing (NGS) of a panel of hematologic malignancy-associated genes at our institution and characterized the clinical and pathological characteristics of patients with germline and somatic POT1 mutations. Of 3323 consecutive patients who underwent NGS, 2770 patients had a hematologic malignancy (lymphoid n = 1299, myeloid n = 934, and both lymphoid and myeloid n = 537), while 553 patients were evaluated for non-malignant cytopenias. All 57 patients (2.06%) carrying either a POT1 disease-associated variant or variant of uncertain significance had a hematologic malignancy compared to no identified POT1 variants in 553 patients with benign cytopenias (OR = 23.5, p < 0.001), suggesting that the presence of POT1 variants was predictive of a hematologic malignancy. Of 57 patients, 33 had lymphoid malignancies, 23 had myeloid neoplasms, and 2 had a lymphoid and myeloid neoplasm (Fig 1). Patient variants were classified as germline or somatic using constitutional DNA sequencing, POT1 emergence/disappearance over time, or POT1 maintenance in remission. In the absence of these data, likely germline or likely somatic designations were made by assessing variant allele frequencies against clinical/pathologic characteristics. 18 patients (33%) were found to have germline or likely germline POT1 variants (29% and 42% in the lymphoid and myeloid malignancy groups, respectively). Another 6 patients (11%) had variants whose germline status could not be determined. Of the 17 unique germline POT1 variants, 10 were missense and located within mapped functional protein domains, while 7 were classified as predicted loss-of-function (pLOF) due to a disruption of start, premature stop, frameshift, or spice site alteration. Patients with hematological malignancies had a ~5-8x increased odds of having a germline pLOF POT1 variant compared to cancer-free individuals in the Genome Aggregation Database (gnomAD, n = 113,108 exomes, OR = 7.5, p < 0.001) or in the Penn Medicine BioBank (PMBB, n = 7877, OR = 5.0, p = 0.010), with a prevalence of 0.25% compared to 0.03% and 0.05%, respectively. Germline pLOF POT1 variants were significantly more enriched in patients with myeloid (gnomAD: OR = 6.1, p = 0.02) and lymphoid (gnomAD: OR = 9.8, p < 0.001; PMBB: OR = 6.5, p = 0.004) malignancies. In 33 patients with lymphoid malignancies and POT1 variants, the most common diagnoses were CLL/SLL (n = 21, germline n = 6, somatic n = 12), CD5- CD10- indolent B cell neoplasms (n = 4, germline n = 1, somatic n = 3), and multiple myeloma (n = 3, all somatic) (Table 1). Lymphoid malignancies with a germline POT1 variant had a relative paucity of additional mutations; in contrast, somatic POT1 variants frequently co-occurred with other mutations, most commonly with TP53 (Fig 2, n = 5, 23%). Among 23 patients with myeloid malignancies, patients with germline POT1 variants developed malignancies at a significantly younger age compared to those whose POT1 variants were somatic (median age 59.5 vs 70.5 years, p = 0.04). The most common diagnosis in patients with myeloid neoplasms carrying germline POT1 variants was MPN (germline n = 5, somatic n = 1). AML, MDS/MPN, and MDS occurred in 4, 3, and 1 patients respectively. All patients with myeloid neoplasms had additional disease-associated mutations, with the most common co-occurring variants in TET2 (n = 7), JAK2 (n = 6, co-occurring with 50% of germline POT1 myeloid variants), and NRAS (n = 6). In conclusion, this is the first comprehensive analysis of POT1 variants in an unselected hospital-based population undergoing molecular testing for variants associated with hematologic malignancies. Our results show that the presence of POT1 variants is predictive of having a hematologic neoplasm and that over 30% of POT1 variants in hematologic malignancy patients are germline. Our study expands the spectrum of POT1-associated familial neoplasms and highlights the needs for better recognition of familial hematologic cancer syndromes. Disclosures No relevant conflicts of interest to declare.

Background:Leukemia cutis (LC) occurs in 10-30% of AML cases and may be a marker of poor prognosis. However, outside of monocytic AML (FAB M4/M5), no clinical or genetic predictors of LC are known. Recently, a number of somatic molecular mutations have been described in AML. Using amplicon-based next-generation sequencing (NGS) of a panel of recurrent, hematologic malignancy-associated mutations, we sought to determine potential molecular markers associated with the development of LC. Methods: A cohort of non-M3 AML patients treated at the University of Pennsylvania was identified in which NGS had been performed on either leukemic blasts obtained during clinical care or from the institutional tissue bank.Average read depth for 33 hematologic malignancy-associated genes was approximately 3000X, minimal depth was 250x, and reporting frequency cutoff for variants was 5%. Mutations were reported as pathogenic or variants of uncertain significance (VUS, further sub-classified internally as likely disease associated, VUS, or likely benign) based on the University’s Center for Personalized Diagnostics (CPD) review of publically available data; only pathogenic or likely disease-associated mutations were included in this analysis. A database maintained by dermatopathology was reviewed to identify cases of leukemia cutis at any time during the disease course. Independent dermatopathology review was obtained for indeterminate cases. Association between presence of each of the 3 most common molecular mutations (FLT3-ITD, DNMT3A, and NPM1) and development of LC was assessed by logistic regression, with adjustment for FAB M4/M5, as appropriate. The association between presence of a molecular mutation in different functional classes (tumor suppressors, activated signaling, chromatin modifiers, transcription factors, splicing machinery) and the development of LC was also assessed. Results:279 adult patients with AML with known molecular genotype were identified. Molecular profile was determined from AML diagnosis in (243, 88%) with the remainder undergoing assessment after prior therapy (relapsed or refractory). 56% were male with median age of 60 years (range 18-87) and median WBC count at diagnosis of 22 K/uL (range 0.4 -388 K/uL; 17% ≥100K/uL). The majority of patients had intermediate cytogenetic risk (12% favorable, 59% intermediate, 23% unfavorable, 6% unknown) and 41% of patients had FAB M4/M5 AML (9% unknown). The three most common mutations were NPM1 (29%), DNMT3A (25%), and FLT3-ITD (23%). NPM1mutations were enriched in patients with FAB M4/M5 AML (41% vs 23%, p=0.003). Leukemia cutis was present in 26 (9%) of patients. NPM1 mutant status was present in 14 of 26 cases of leukemia cutis (OR 3.17, 95% CI 1.40-7.20, p=0.006). No association was detected for LC and the presence of mutant FLT3-ITD (OR 1.27, p=0.613), mutant DNMT3A (OR 1.7, p=0.224), or a mutation in any functional class of AML mutations (all p-values NS). The impact of NPM1 mutant status remained significant after adjustment for association with M4/M5 AML (OR 3.91, p=0.005). As the histologic subtype of AML might modify the association between NPM1 mutations and leukemia cutis, we next examined the impact of NPM1 mutant status on patients with FAB M4/M5 AML and non-M4/M5 AML. Among patients with M4/M5 AML, 10/12 (80%) patients with LC were NPM1 mutant compared to 32/91 (35%) without LC suggesting that the presence of mutated NPM1 was significantly associated with the development of LC (OR 9.22, p=0.006). Among patients with non-M4/M5 AML, 3/9 (33%) of patients with leukemia cutis were NPM1 mutant compared to 32/142 (22.5%) without LC indicating no association in the non-M4/M5 subgroup (OR 1.72, p=0.461). Interestingly, M4/M5 AML was not associated with LC in the NPM1 WT cohort (OR 0.65, p=0.6). Conclusion: Using NGS, we identify a novel association between NPM1 mutation status and the presence of leukemia cutis, particularly within monocytic AML. Confirmation of these observations in a larger dataset is planned. Our data suggest potential cellular effects of NPM1 mutation affecting homing of leukemic blasts to skin and support the World Health Organization’s provisional classification of NPM1-mutated AML as a distinct biologic entity. Disclosures No relevant conflicts of interest to declare.