Comprehensive Genomic Profiling of Advanced Anal Adenocarcinoma.

4 Background: Anal adenocarcinoma (anal AD) is a rare and aggressive gastrointestinal malignancy. Because of its rarity, no standard therapy is established and treatment strategy for advanced rectal adenocarcinoma (rectal AD) is extrapolated. Little is known for genetic alterations (GAs) and their therapeutic implications in advanced anal AD. We aim to investigate to clarify genomic profiles of advanced anal AD in comparison of advanced rectal AD. Methods: We retrospectively extracted data on patients with advanced anal AD and advanced rectal AD who underwent comprehensive genomic profiling (CGP) tests and were registered for the Center for Cancer Genomics and Advanced Therapeutics (C-CAT) in Japan. CGP tests were performed by NCC Oncopanel or FoundationOne CDx. We examined somatic GAs, microsatellite instability (MSI) status, and tumor mutation burden (TMB). TMB-high was defined as ≥10 mutations/Mb. Actionable GAs were counted if they were classified as “pathogenic/oncogenic” or “likely pathogenic/likely oncogenic” variants. Druggable GAs are actionable GAs with approved drugs for anal AD or other types of cancer or clinical trials showing efficacy for either anal AD or different types of cancer. Results: From June 2019 to April 2023, 45 patients with anal AD and 1915 patients with rectal AD were enrolled into the C-CAT database. In the anal AD group, most common actionable GAs were TP53 (89%), KRAS (51%), ERBB3 (22%), MYC (20%), SMAD4 (20%), and ERBB2 (11%). Compared with the rectal AD group, the anal AD group had a significantly higher frequency of actionable GAs in ERBB3 (22% vs. 2%, p < 0.01), MYC (20% vs. 8%, p < 0.01), and BRCA2 (7% vs. 1%, p < 0.01), and a significantly lower frequency of actionable GAs in APC (7% vs. 85%, p < 0.01). The proportion of MSI-high and TMB-high in the anal AD group and the rectal AD group were 0% vs. 0.2% (p = 0.79), and 7% vs. 5% (p = 0.54). Common druggable GAs in anal ADs included KRAS G12D mutation (22%), ERBB2 amplification (7%), BRCA2 mutation (7%), BRAF V600E mutation (2%). Compared with the rectal AD group, the anal AD group had a significantly higher frequency of druggable GAs in BRCA2 mutation (7% vs. 1%, p < 0.01). Conclusions: The present study showed that anal AD had a different profile of GAs compared with advanced rectal AD. CGP tests are useful tool for identifying druggable GAs in advanced anal AD for expanding therapeutic opportunities.