ERAP1 and cancer: ERAP1 and ERAP2 [endoplasmic reticulum aminopeptidase 1 and 2, which form a protein complex (25)], both play a role in peptide trimming for presentation on major histocompatibility complex (MHC) class I, and are both targeted by tosedostat, which is currently in development for the treatment of cancers (fig.