In Japan, cancer immunotherapy using immune checkpoint inhibitors(ICIs)has become a new treatment modality in cancer chemotherapy in the 2010s, and is now widely approved for many types of cancer. Today, combination cancer immunotherapy utilizing ICIs is being developed, with many cancer types. The first approved ICI combination in Japan consists of nivolumab, an anti-PD-1 antibody, and ipilimumab, an anti-CTLA-4 antibody. In the combination therapy, ipilimumab is administered at different doses, intervals, and frequencies depending on the cancer type. ICI combination therapy has been reported to be more effective than ICI monotherapy, but also be associated with more severe adverse events. Therefore, optimal dosing strategies for ipilimumab were explored considering both treatment efficacy and adverse event profiles. In the study of 64 cases with multiple cancer, higher efficacy of ICI combined therapy was expected in cases with irAEs, and there were cases with long-lasting efficacy even after early discontinuation of ipilimumab due to irAEs. And the high dose(3 mg/kg)of ipilimumab was suggested to be an independent risk factor for CTCAE Grade 3 or higher for severe irAEs.