IDO1 and endometrial cancer: Endometrial cancer cells utilize several immune escape strategies, including enhanced expression of checkpoint regulators such as programmed cell death protein 1 (PD-1) and PD-L1, impaired antigen presentation due to reduced major histocompatibility complex class I (MHC I) expression, and enzymatic activation of immunosuppressive mediators like indoleamine 2,3-dioxygenase 1 (IDO1).