Fibroblast activation protein-α (FAP) is a type II integral serine protease that is specifically expressed by activated fibroblasts. FAP-α displays both exopeptidase and endopeptidase/gelatinase/collagenase activities. FAP-α protein and/or activity have been associated with fibrosis, inflammation and cancer, but the protein is undetectable in most normal tissues. Cancer-associated fibroblasts (CAFs) in the tumor stroma have an abundant and stable expression of FAP, which plays an important role in promoting tumor growth, invasion, metastasis, and immunosuppression. CAF overexpression of FAP promotes tumor development and metastasis by influencing extracellular matrix remodeling, intracellular signaling, angiogenesis, epithelial-to-mesenchymal transition, and immunosuppression.