Current status of immune checkpoint inhibitors for gastric cancer.

Recent breakthrough results from immune checkpoint inhibitors (ICI) have paved the way to a new era of cancer immunotherapy. In particular, inhibition of programmed death-1 (PD-1)/programmed death-ligand 1 (PD-L1) axis with ICI including nivolumab and pembrolizumab has been emerging as a novel treatment strategy for advanced gastric cancers (GC). In a meta-analysis for anti-PD-1/PD-L1 therapy in GC, the objective response rate was 12.0% and the disease control ratio was 34.7%. The ICI treatment in GC provided modest survival benefit and especially, anti-PD-1 treatment could improve the 12-month and 18-month overall survival rate and prolonged the duration of the response. Moreover, it is likely that anti-PD-1/PD-L1 therapy is more effective in subgroups with microsatellite instability-high, Epstein-Barr virus-positive or high mutation burden in advanced GC. The next steps for developing ICI in GC are mainly two challenges as follows. First is the identification of accurate biomarkers that can predict the response to ICI. The second challenge is the clinical development of combinatorial approaches to maximize the efficacy of ICI. In this review, recent advances in ICI for GC are discussed from a viewpoint of translational aspect including biomarkers and tumor microenvironment, and from a viewpoint of clinical aspects including combination therapies.