FAP and neoplasm: Fibroblast activation protein (FAP) expression is highly specific and have a property of tumor promoting in various types of tumors, although CAFs are known to have heterogeneity and have various specific markers, including alpha smooth muscle actin (αSMA), vimentin, platelet-derived growth factor receptor (PDGFR), and fibroblast specific protein-1 (FSP-1)15,16.