PDCD1 and neoplasm: Tumours have evolved in multiple ways to evade the immune system by creating a strong immunosuppressive microenvironment, which protects tumour cells from the immune attack by exploiting inhibitory immune checkpoints such as the programmed cell death ligand-1 (PD-L1)/programmed cell death-1 (PD-1) axis, using check point inhibitors (CKI) [8].