Anal melanoma: A comparative comprehensive genomic profiling study.

Abstract

9566 Background: We performed a comprehensive genomic profiling (CGP) study of AM and CM to learn of potential genomic alterations (GA) linked to targeted and immune checkpoint inhibitor (ICPI) therapies. Methods: 90 AM and 1804 CM FFPE tissues from late stage 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. PD-L1 expression was determined by IHC. Results: AM and CM had a similar age, but AM females and CM males were significantly more common (P < 0.0001). GA/tumor was significantly higher in CM (UV light exposure) as were the median TMB and frequency of TMB ≥ 10 and 20 mutations/Mb (P < 0.0001 for all comparisons). PD-L1 expression was higher in AM than CM (P = 0.0023). AM and CM were all MS-stable. The contrast in S FB1 mutations in AM and TERT GA in CM were significant (P < 0.0001). Of potentially targetable GA, AM featured significantly more KIT GA than CM (P < 0.0001), whereas CM featured significantly more BRAF GA (P < 0.0001). Only 11% of AM BRAF GA were V600E whereas 74% of CM BRAF GA were V600E (P < 0.0001). MTOR pathway GA were common in both tumor types. Additional potentially targetable alterations in PDGFRA and ERBB2 kinases were seen in AM but not in CM. Conclusions: CM is distinct from AM featuring higher GA/tumor, higher TMB and frequent BRAF V600E GA that predict benefit from ICPI and anti-BRAF therapies. Although both AM and CM feature MTOR pathway targets, AM does have higher PD-L1 expression than CM and is characterized by an array of potentially targetable kinase genes including KIT, PDGFRA, ERBB2 and to a lesser extent than CM, BRAF.[Table: see text]