Tumor mutation burden as a biomarker in resected gastric cancer via its association with immune infiltration and hypoxia

Background Tumor mutation burden (TMB) predicts immunotherapy efficacy in solid tumors. However, the biomarker role of TMB is still conflicting in resected tumors. We aimed to examine the association of TMB with prognosis and postoperative chemotherapy (CT) or radiochemotherapy (RCT) efficacy in resected gastric cancer (GC). Methods Whole-exome sequencing (WES) was performed in 73 resected GC specimens. Validation cohorts included 352 patients from The Cancer Genome Atlas (TCGA) and 222 patients from the Asian Cancer Research Group (ACRG). Immune infiltration and hypoxia were evaluated by transcriptome data and immunohistochemistry assay. Results TMB-high GC had favorable overall survival (OS) and disease-free survival (DFS), but the OS and DFS benefits with postoperative CT/RCT were more pronounced in TMB-low GC. These findings were consistent among all three cohorts and were maintained in the pooled cohort. Stratified by stages in the pooled cohort, stage III GC benefited from postoperative CT/RCT regardless of TMB level while stage Ib/II GC benefited from postoperative CT/RCT in TMB-low but not in TMB-high subgroup. TMB positively correlated with immune infiltration which was characterized by NK cell rather than CD8 + T cell enrichment. TMB-high GC was more hypoxic than TMB-low GC, and TMB-high stage Ib/II GC was the most hypoxic. Conclusions High TMB may predict favorable prognosis in resected GC but poor response to postoperative CT/RCT in stage Ib/II subgroup, which may be determined by TMB-associated immune infiltration and hypoxia, respectively.