Programmed Death-Ligand 1 (PD-L1), CD274, or B7 Homolog 1 (B7-H1), is a transmembrane protein involved in suppressing the immune system and rendering tumour cells resistant to lysis through binding of the Programmed Death-1 (PD-1) receptor. Overexpression of PD-L1 may allow cancer cells to evade the actions of the host immune system. In renal cell carcinoma, upregulation of PD-L1 has been linked to increased tumour aggressiveness and risk of death.