While prolidase is described as an intracellular enzyme27, IHC staining using an antibody to prolidase overlapped with extracellular matrix (ECM) in both human PDAC and PKI tumours (Fig. 1d) and we also found that prolidase was excreted into the media from PDAC cells grown in culture (Fig. 1e). This evidence concerns the gene PEPD and neoplasm.