Abstract 2356: Novel and recurrent germline mutations in Colombian families with colorectal cancer syndromes

Abstract Hereditary colorectal cancer (CRC) syndromes accounts for approximately 5-10% of total CRC cases. Among those, Lynch syndrome (LS) is the most frequent, but the penetrance depends on the mismatch repair gene (MMR) affected. On the other hand, the Familial Adenomatous Polyposis (FAP) syndrome is less frequent, but with penetrance near to 100%. In Colombia we don't know the prevalence of these syndromes. In the National Cancer Institute from Colombia, the largest reference cancer center in the country, we aim to performed germline genetic analyses in Colombian CRC patients with a suspected hereditary cancer syndrome, as part of the Hereditary Cancer Program that seeks to identified high risk families to offer preventive measures and screening recommendations. A total of 66 patients with CRC fulfilling criteria have been so far analyzed with Next Generation Sequencing using a multigene panel. From those, the 32% have negative results, 41% have VUSs and 27% have positive results (meaning a pathogenic or potentially pathogenic genetic variant). The most prevalent CRC syndrome is Lynch (11/18, 61% with MMR mutated genes), followed by polyposis syndromes such as FAP (11% APC) and MAP (1.5% biallelic MUTYH). Most of our Lynch syndrome families fulfilled Bethesda or Amsterdam criteria. Two recurrent mutations in MLH1 were found in Lynch syndrome families (6/11, 54.5%), which are MLH1: c.1918C>T (p.Pro640Ser) and MLH1: c.790+1G>A. Further haplotype analysis will help us to determine if mutation carriers shared a common ancestry. Citation Format: Ana Lucía Rivera-Herrera, Ana Milena Gómez-Camargo, Martha Lucía Serrano-López, Luis G. Carvajal-Carmona, María Carolina Sanabria-Salas. Novel and recurrent germline mutations in Colombian families with colorectal cancer syndromes [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2356.