Although it is well-known that PD-1 and PD-L1 inhibitors have high reactivity in PD-1-positive gynecological cancer patients and ICI inhibitor reactivity is high in endometrial cancer in MSI-H or d-MMR environments, in order to effectively apply such immunotherapy in the treatment of gynecological cancer, it is crucial to understand the mechanisms of action of anti-PD-1, anti-PD-L1, and anti-CTLA-4 agents and how immunotherapy is performed in gynecological cancers. This evidence concerns the gene CD274 and endometrial cancer.