PDCD1 and neoplasm: Tumor cells and their niches in many types of cancer, including melanoma, lung carcinoma, breast cancer, bladder cancer, pancreatic cancer, and ovarian cancer, can also express PD-L1.3 The engagement of T-cell PD-1 by PD-L1 expressed on tumor cells can inhibit the T-cell activation, negatively regulating adaptive immune responses, ultimately leading to tumor evasion of immunosurveillance and poor patient prognosis.