PDCD1 and neoplasm: Based on the research outcomes about the role of ICs in the tumor microenvironment or autoimmunological diseases, we hypothesize that the PD-1/PD-L1/PD-L2 pathway may play a significant role in the implantation and growth of endometrial tissue in the peritoneal cavity, and may be related to the local immunosuppression in patients suffering from EMS.