PREP and cancer: Prolyl oligopeptidase(PREP, EC 3.4.21.26, also POP or PEP) isa serine protease with endopeptidase activity, cleaving peptides upto ca 30 amino acids after a proline residue.1,2 PREPis linked to several diseases and pathological processes such as neurodegenerativediseases, cancer, and inflammation (for a review, see Svarcbahs etal.3).