UC Berkeley

BACKGROUND: Gastric cancer (GC), a molecularly heterogeneous disease, is the third leading cause of cancer death worldwide. The majority of GC cases worldwide occur in East Asia, predominantly China. Mutational Signature Framework offers an elegant approach to identify mutational processes present in tumors. METHODS: To identify mutational signature patterns, we conducted whole exome sequencing (WES) analysis in Chinese patients with GC. Mutect2 and MutsigCV were used to identify significantly mutated genes in 175 Chinese GC cases using paired tumor-normal tissues. We investigated mutational signatures using Catalogue of Somatic Mutations in Cancer (COSMIC) Version 2 (V2) and Version 3 (V3). RESULTS: We identified 104 mutated genes with P < 0.01. Seven genes (OR6B1, B2M, ELF3, RHOA, RPL22, TP53, ARIDIA) had q < 0.0001, including six previously associated with GC. Mutational signatures (COSMIC-V3) observed include 14 single base substitutions (SBS), one doublet base substitution (DBS) Signature A, and one InDel (ID2). The most frequent SBS signatures (SBS05, SBS01, SBS15, SBS20, SBS40) were also observed in 254 White GC cases from The Cancer Genome Atlas (TCGA) Project. However, SBS01 and SBS20 showed significant differences between Whites vs. All Asians (19.3% vs. 11.3% for SBS 1 (P = 0.012) and 11.4% vs. 5.9% for SBS20 (P = 0.025), respectively). Using COSMIC V2, signatures 6, 15, and 1 were the most frequent in Chinese GC cases. Further, most Chinese GC cases carried multiple signatures. CONCLUSIONS: This effort represents the most detailed mutational signatures analysis of GC cases from China to date. Results hold promise for new insights in understanding risk and prognosis factors in GC.