A key characteristic of carcinoma-associated fibroblasts (CAFs) is the expression of fibroblast activation protein (FAP) α. FAP is a type II transmembrane protein which has both dipeptidyl peptidase and endopeptidase activities, cleaving substrates at a post-proline bond. FAP expression is difficult to detect in non-diseased adult organs but is greatly upregulated in sites of tissue remodeling, which include liver fibrosis, lung fibrosis, atherosclerosis, arthritis, tumors, and embryonic tissues. https://www.creative-biolabs.com/adc/anti-fap-antibody-development.htm