Abstract 7334: Germline mutations in cancer susceptibility genes in patients with mucosal melanoma

Abstract Background: Mucosal melanoma (MM) is the rarest subtype of melanoma with markedly worse outcomes compared to cutaneous melanoma (CM). Unlike CM which is driven by somatic mutations due to UV exposure, risk factors for MM are less defined. While germline mutations in cancer susceptibility genes are well-studied in CM, they are less understood in MM. Herein, we aimed to identify the prevalence of germline mutations in cancer susceptibility genes in a large MM cohort. Methods: A cohort of 247 MM patients (pts) from MD Anderson Cancer Center with available blood for germline sequencing was identified. Pt characteristics were reflective of U.S. MM population with median age of 63, 60% females and 84.6% white. Clinicodemographic features of pts including tumor site, key somatic mutations (BRAF, NRAS, KIT) and personal history of other malignancies were abstracted, and their frequencies were compared in pts with and w/o germline mutation. Frequency of MITF and CHEK2 alleles were compared to expected population control rate based on TOPMED by Fisher’s exact test. Results: Among 247 pts, 10.9% had germline mutations, primarily in MITF (c.G952A:p.E318K) (2.4%) and CHEK2 (c.1100delC:p.T367fs) (1.6%) at OR of 13.9 (95%CI 5.0, 30.9) and 16.4 (4.4, 42.9) compared to population control rate (Table 1). MM sites of origin were gastrointestinal (36%), genitourinary (34%) and head & neck (30%). In terms of somatic mutations, KIT (26%) was most common, followed by NRAS (15%), non-V600E BRAF (6.5%) and BRAF V600E (2.4%). These variables did not differ between those with and w/o germline mutation. Pts with germline mutation had a higher incidence of non-melanoma malignancies (48% vs 29%; p=0.044). Table 1. Summary of identified germline mutations in the mucosal melanoma cohort. Germline mutation Protein MITF (N= 6) p.E318K CHEK2 (N=4) p.T367fs MUYTH p.G368D ATM splice ATM p.L263fs ATM p.R1875X ATM p.L1327X ATM p.A2067D ATM p.R2034X BRCA2 p.A1689fs CHEK2 p.S400T ERCC3 p.R109X MITF p.C29Y NF1 p.L1183R PALB2 p.V221X POLE p.D287E TP53 p.R306X TP53 p.V73Wfs*50 TSC1 p.Q844X Conclusions: This study reports a high prevalence of germline cancer susceptibility mutations in the largest cohort of MM to date, including mutations which are actionable. There is overlap with known MITF risk alleles for CM. We are currently performing a GWAS to comprehensively understand the genetic architecture of risk in MM. Citation Format: Afsaneh Amouzegar, Xiaogang Wu, James Long, Sabitha Prabhakaran, Latasha Little, Curtis Gumbs, Jared Malke, Julie Simon, Jianhua Zhang, Jennifer Wargo, Paul Scheet, Justin W. Wong, Priyadharsini Nagarajan, Jennifer L. McQuade, Andrew Futreal. Germline mutations in cancer susceptibility genes in patients with mucosal melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7334.