Anal Melanoma: A Comparative Comprehensive Genomic Profiling Study.

551Background: Anal melanomas (AM) share histologic features with cutaneous melanomas (CM), are highly aggressive and behave in a distinct clinicopathologic pattern. We performed comprehensive genomic profiling (CGP) of AM to learn of potential matched targeted and immunotherapies that may improve clinical outcomes for the disease. Methods: FFPE tissues from late stage AM (81 cases) and CM (1804 cases) underwent hybrid-capture based CGP to evaluate all classes of genomic alterations (GA). Tumor mutational burden (TMB) was determined on up to 1.1 Mbp of sequenced DNA and microsatellite instability (MSI) was determined on 114 loci. Results: AM and CM had a similar age, but AM females and CM males were significantly more common (P u003c 0.0001) (Table). Given the UV light exposure in the CM, the GA/tumor was significantly higher than AM as were the median TMB and frequency of TMB ≥ 10 and 20 mutations/Mb (P u003c 0.0001 for all comparisons). All AM and CM were MS-stable. The contrast in SFB1 mutations in AM and TERT...