FAP and cancer: Fibroblast activating protein (FAP) is a type II transmembrane serine protease that is highly expressed as a dimer on the surface and matrix of up to 90% of epithelial cancer tumor-associated fibroblasts (CAFs) [1,2], especially in breast cancer, colorectal cancer, pancreatic cancer, cervical cancer and other malignant tumors characterized by proliferative hyperplasia reaction of connective tissue [3].