Diffuse type gastric cancer (DGC), a pathological subtype, is one of the most common malignant solid tumors, and mortality of this tumor is not negligible, especially in early-onset cancer patients. In fact, affirmative personalized treatments based on gene profile have not been established yet. The aim of this study was to provide the possible genotype-matched treatment for DGC through comprehensive examination of genomic variants and analysis of clinicopathological characteristics. We retrospectively studied 23 formalin-fixed, paraffin-embedded samples of patients diagnosed as DGC between January 2003 and December 2015 at the Department of Cancer Pathology, Hokkaido University Graduate School of Medicine. The cases were divided into two groups: early-onset (< 50 years old) and elderly-onset (≥ 50 years old) DGC groups. We performed targeted genomic sequencing using a 163 cancer-related gene panel. The sequencing data were analyzed using an original bioinformatics pipeline called GenomeJack and were clinicopathologically evaluated. Intestinal metaplasia and atrophy were highly observed in the adjacent non-cancerous mucosa in the elderly-onset DGC group compared with those in the early-onset DGC group. The number of somatic variants was significantly higher in the elderly-onset DGC group than in the early-onset DGC group. Fifteen patients (65.2%) harbored at least one genomic alteration of the potential target for genotype-matched treatment. In addition, one patient with hypermutation phenotype was diagnosed as Lynch syndrome due to MLH1 mutation, suggesting the sensitivity for the treatment with immune checkpoint inhibitors. Not only does our study demonstrated the potential utility of the targeted genomic sequencing approach for making informed therapeutic decisions, but it also sheds light on DGC pathogenesis and progression.
Keywords: Cancer gene profiling test; Gastric cancer; Genomic alteration; Genotype-matched treatment; Next generation sequencing (NGS); Precision medicine.