PDCD1 and neoplasm: Programmed cell death 1 ligand 1 (PD-L1) is often overexpressed in tumour cells and is an apoptotic process to bind to PD-1 in vivo, signaling immunosuppression and reducing T cell proliferation and activation, which suggests that the PD-1/PD-L1 pathway is a mechanism of tumour immune escape (5, 6).