PVR and breast cancer: Also, In breast cancer, malignant cells can circumvent host immune responses via various mechanisms of immune evasion, including the upregulation of immune checkpoint ligands such as programmed death ligand 1 (PD-L1), PD-L2, poliovirus receptor (PVR; CD155), and galectin-9 (Gal-9) [[8], [9], [10]].