FAP, also known as fibroblast activation protein-alpha (FAP-alpha) is a cell surface glycoprotein serine protease, which can participate in extracellular matrix degradation and is involved in many cellular processes including tissue remodeling, fibrosis, wound healing, inflammation and tumor growth. FAP is a single transmembrane protein that locates the cytoplasm and plasma membrane. Immunohistochemical studies have shown that FAP is transiently expressed in certain normal fetal mesenchymal tissues but that normal adult tissues as well as malignant epithelial, neural, and hematopoietic cells are generally FAP-negative. However, most of the common types of epithelial cancers contain abundant FAP-reactive stromal fibroblasts.