Background: A large study of intratumoral heterogeneity (ITH) in gastric cancer (GC) somatic mutations, a crucial consideration for effective druggability, has not been published. This study used targeted multi-regional sequencing (MSEQ) of gastric tumor DNA to examine cancer gene mutations, with the hypothesis of widespread ITH. Methods: MSEQ was carried out with a panel of> 700 cancer-associated genes in 115 tumor biopsies from 32 patients. Analyses focused on identifying clonal and subclonal mutations in genes targetable with
