Cancer-associated fibroblasts (CAFs) are elongated, spindle-shaped activated fibroblasts characterized by some positive markers, such as alpha-smooth muscle actin (α-SMA), fibroblast activation protein (FAP) and fibroblast specific protein 1 (FSP-1), as well as caveolin-1 (CAV-1), FSP-1, PDGFR-α, PDGFR-β and Thy-1 [222,223]. Here, FAP is linked to cancer.