Abstract C158: Contribution of multi-organ cancer predisposition genes for gastric cancer risk of different histological subtypes

Abstract Approximately 10% of gastric cancer (GC) cases exhibit familial clustering, yet only 1-3% can be explained by known hereditary syndromes, being Hereditary Diffuse Gastric Cancer (HDGC) the most well-established disease predisposing for diffuse gastric cancer. Familial intestinal gastric cancer (FIGC) has been defined clinically, but it remains mostly genetically unexplained. Likewise, the heritability of mixed GC remains to be uncovered. We aimed to estimate the frequency of known cancer predisposition gene variants in GC cases with family history of cancer and/or early onset. We evaluated the contribution of pathogenic and likely pathogenic (P/LP) variants in well-established and multi-organ cancer predisposition genes for GC risk in a large multi-center study involving 750 GC patients, either by targeted sequencing or whole exome sequencing. We identified 45 patients (6%) with P/LP variants in ATM (17 cases), BRCA2 (10 cases), MLH1 (five cases), TP53 (three cases), BRCA1, PALB2, RAD51D and CHEK2 (two patients each), and RAD51C and PMS2 (one case each), all mutually exclusive. The P/LP variant prevalence was higher in intestinal (9.8%) than in diffuse (4.3%) or mixed GC (4.5%) (p-value=0.023), with no clear difference per mutated gene by histological subtypes. Only sixteen of the 45 variant carriers fulfilled the criteria for genetic testing of at least one cancer predisposition syndrome. Our findings indicate that multi- organ cancer predisposition genes should be included in gene panels used for investigating germline variants in GC patients, especially when there is family history of cancer but irrespective of histology subtype, as this would increase the chance of identifying patients that might benefit from prevention and targeted treatment strategies. Citation Format: Ana P. Estrada-Florez, Paul C. Lott, Luis G. Carvajal Carmona. Contribution of multi-organ cancer predisposition genes for gastric cancer risk of different histological subtypes [abstract]. In: Proceedings of the 17th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2024 Sep 21-24; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2024;33(9 Suppl):Abstract nr C158.