Gastrointestinal cancer treatment with immune checkpoint inhibitors

Immuno-oncological treatment approaches, particularly with the use of immune checkpoint inhibitors such as anti-programmed death 1 (PD-1)/programmed death ligand 1 antibody or anti-cytotoxic T-lymphocyte associated protein 4 antibody, have become the standard treatment for gastrointestinal cancers. However, gastrointestinal cancers show an overall modest tumor response to immune checkpoint inhibitors. Nevertheless, subgroups such as tumors that are DNA mismatch repair-deficient or have high microsatellite instability particularly benefit from immune checkpoint inhibitors. Even in the first-line setting for colorectal cancer, the clinical efficacy of pembrolizumab, an anti-PD-1 antibody, was superior to that of chemotherapy. Recently, a combination of atezolizumab, an anti-programmed death ligand 1 antibody, and bevacizumab was approved as the first-line treatment for hepatocellular carcinoma, and was reported as superior to sorafenib. Nivolumab, an anti-PD-1 antibody that is added to chemotherapy as the first-line treatment for gastric cancer, resulted in longer survival compared with chemotherapy alone. Further studies are ongoing to investigate additional immune checkpoint inhibitors for other gastrointestinal cancers. This review aims to provide an overview of the results of clinical trials for immune checkpoint inhibitors in gastrointestinal cancers, including colorectal cancer, gastric cancer, hepatocellular carcinoma, pancreatic cancer, and biliary tract cancer.