During the process of tumor progression, the tumor cells ultimately evolve mechanisms of immunosuppression or escape, such as loss or down-regulation of MHC expression as well as up-regulation of different pathways, including programmed death ligand-1 (PD-L1), immune-checkpoint molecules (CD47), and NK-cell ligands (FAS, FAS ligand (FASL)), and thus can actively proliferate in escape phase 31. Here, FAS is linked to neoplasm.