CTSE and cancer: Cathepsin E (CTSE) is an intracellular aspartic protease that is normally expressed in a wide range of immune cells but also is present in osteoclasts and gastric epithelial cells; secreted forms have been described.8–10 A differential expression pattern has been demonstrated for CTSE in normal, metaplastic, dysplastic, and neoplastic gastric epithelium as well as in the intestinal dysplasia–neoplasia sequence in APCmin/+ mice.11–15 Furthermore, CTSE has also been suggested as both a diagnostic and a prognostic biomarker for some cancers.16