ANPEP and cancer: Whereas genetic alterations in genes encoding members of the MHC-I/APM or regulatory pathways (e.g., the IFN-γ response pathway) cause irreversible MHC-I defects (15, 16), transcriptional repression of MHC-I genes is also observed in a number of tumor entities (17, 18) and contributes to resistance to cancer immunotherapy (19).