Fibroblast Activation Protein (FAP) is a member of the serine protease family, exhibiting dipeptidyl peptidase and endopeptidase activities. It is a transmembrane protein primarily expressed in cancer-associated fibroblasts in the tumor microenvironment and during tissue repair processes. FAP plays a role in extracellular matrix remodeling, tumor proliferation, migration, and immune regulation. By cleaving extracellular matrix proteins and modulating signaling pathways, FAP is involved in pathological processes such as tumor invasion and metastasis. Gene expression is relatively low in normal tissues but highly expressed in various human solid tumors. Changes in FAP expression or gene mutations are associated with tumor development and tissue fibrotic diseases.