Abstract

10578 Background: Gastric cancer (GC) is the fourth leading cause of cancer-related deaths worldwide. The role of pathogenic/likely pathogenic variants (PVs) in cancer predisposition genes is not well understood. We aimed to assess the prevalence of PVs in GC patients undergoing germline genetic testing (GGT) via multi-gene panel testing (MGPT) at a large commercial laboratory. Methods: Retrospective review of MGPT (>10 genes) in GC patients at a large commercial laboratory (Invitae Corp.) from March 2015 to July 2023 was performed. GC included diffuse type, intestinal type or unspecified type, as provided by ordering clinicians. Association of patient characteristics with positive GGT results was assessed with logistic regression with a significance threshold of p < 0.05. Results: 3,706 GC patients underwent GGT(Table). Overall, 495 (13.4%) patients were found to carry ≥1 PV, including 29 patients with 2 PVs and 3 patients with 3 PVs. GGT was negative in 1,890 (51.0%) patients, 1,199 (32.4%) had a variant of uncertain significance-only and 121 (3.3%) carried a single PV in a gene associated with autosomal recessive inheritance. PVs were identified in 38 genes; 77.7% (385/495) were in a gene previously associated with GC, primarily the homologous recombination repair genes ( BRCA1, BRCA2, PALB2and ATM, 34.9%), the Hereditary Diffuse Gastric Cancer genes ( CDH1and CTNNA1, 19.6%) and mismatch repair genes ( MLH1, MSH2, MSH6, PMS2and EPCAM, 17.4%). Males were more likely to carry a PV than females (OR 1.4, 95% CI 1.1-1.7) and having a personal history of another cancer increased the odds of carrying a PV (OR 1.3, 95% CI 1.0-1.7). Age, number of genes tested and histology were not significantly associated with PV. Conclusions: In this large study of GGT in GC patients, the prevalence of PVs in cancer associated genes was 13.4%, higher than previous estimates of 3-5%. PVs were predominantly in genes associated with GC. Male sex and history of other cancers were associated with a PV. Limitations include incomplete histologic data, varying panel size, and ascertainment bias as patients may have had additional personal/family history that prompted GGT. These results support consideration of GGT in all GC patients as prevalence of PVs is similar to other cancer types for which guidelines recommend universal genetic testing.[Table: see text]