Germline pathogenic variants in a large convenience cohort of multiple melanoma subtypes.

9595 Background: A heritable component accounts for approximately 10% of melanomas. These estimates derive from populations deemed high risk for a germline pathogenic variant (gPV). The prevalence and clinical features of a broader melanoma patient population are unknown. Methods: Using the MSKCC IMPACT dataset, we identified a convenience cohort of all pts with melanoma who had undergone targeted tumor-normal sequencing (NCT01775072) for gPV in 76-90 genes. gPV were categorized by association with cancer predisposition and penetrance. Results: 701 pts with melanoma and germline sequencing demonstrated 105 pathogenic variants in 29 genes (Table). 14% of pts (n=99) harbored a gPV in a cancer susceptibility gene (gPV+); 49% high/moderately pathogenic, 32% low/recessive, and 19% uncertain. 6% of gPV+ pts had 2 gPVs. 77% of gPVs were involved in DNA damage repair pathways. The genes known to be associated with melanoma risk accounted for 9% of gPVs, inclusive of CDKN2A (2%), CDK 4 (1%), MITF (4%), and BRCA2 (2%). A further 15% were in genes with suggested, as yet undefined, susceptibility for melanoma; BRCA1 (6%), ATM (5%), BAP1 (2%) and PALB2 (2%). gPV+ frequency varied by melanoma subtype: unknown primary (19%, n=18), cutaneous (15%, n=64), mucosal (13%, n=13), acral (7%, n=2) and uveal (4%, n=2) (p=0.039). No significant difference in age, sex, race, stage at diagnosis, personal history of other cancer, or family history (FHx) of melanoma was seen between gPV+ and gPV-, on univariate analysis. 47% of gPV+ pts had either >1 primary melanoma, age1 risk factor. The presence of >1 melanoma and FHx of melanoma was associated with gPV+ (p=0.016). There was no significant difference in somatic TMB and MAPK pathway alterations between gPV+ and gPV-. In this cohort selected for high-risk melanomas, melanoma was the first presenting cancer for 83% of patients with gPV+. Assessment of biallelic loss to clarify if gPVs may be driving melanoma carcinogenesis is ongoing. Conclusions: This represents the largest cohort of sequenced matched germline and somatic analysis in melanoma. There is a 14% overall gPV prevalence that varies by melanoma subtype. The association of >1 primary melanoma, young age and a family history of melanoma with gPV+ is consistent with prior studies, however, would not capture 53% of gPV+ in this cohort. Melanoma represents the index cancer for the majority of gPVs, informing the need to expand germline testing in patients with melanoma. Table: see text