FAP and cancer: As a type II transmembrane serine protease, fibroblast activation protein (FAP) belongs to the dipeptidyl peptidase (DPP) 4 protein family and is highly expressed in the cancer-associated fibroblasts in about 90% of normal human epithelial tumors (Garin-Chesa et al., 1990; Scanlan et al., 1994; Hamson et al., 2014; Gascard and Tlsty, 2016).