In cases of pleural mesothelioma, the immune checkpoint inhibitor nivolumab, an anti-programmed cell death-1 monoclonal antibody, has been shown to be efficacious in patients refractory to pemetrexed.[5,6] However, the effects of immune checkpoint inhibitors on the progression of peritoneal mesothelioma have not been reported. This evidence concerns the gene PDCD1 and peritoneal mesothelioma.