PDCD1 and ovarian cancer: Ovarian cancer is characterized by high relapse and treatment resistance rate (7), but it is considered to be the “immunogenic tumors.” In the recent years, immune therapies such as immune checkpoint blockades (ICBs) have been developed rapidly and investigated as potential maintenance treatments in ovarian cancer, including anti–PD-1 (programmed cell death protein 1), anti–PD-L1 (programmed cell death ligand 1), and anti–CTLA-4 (cytotoxic T lymphocyte-associated antigen-4) (8, 9).