PDCD1 and Epstein-Barr virus infection: In particular, it has been hypothesized that programmed cell death ligand 1 (PD-L1) and programmed cell death protein-1 (PD-1), crucial immune checkpoints aimed at inhibiting and escaping immune surveillance, are also implicated in non-familial SBC as well as in colorectal and gastric cancers with MSI and/or Epstein-Barr Virus (EBV) infection [47,48].