Fibroblast Activation Protein alpha subunit (FAPa or FAP, alpha) is a integral membrane gelatinase belonging to the serine protease family. FAPa is the alpha subunit and DPP4 (CD26) the beta subunit of a heterodimeric membrane-bound proteinase complex also known as 170 kDa Melanoma Membrane Gelatinase, Integral Membrane Serine Proteinase and Seprase,which also has subunit molecular weight as 88 kDa,95 kDa, 97kDa. Some cells make only FAPa homodimers, some only DPP4 homodimers. The monomer is inactive. FAP, alpha is selectively expressed in reactive stromal fibroblasts of epithelial cancers, granulation tissue of healing wounds, and malignant cells of bone and soft tissue sarcomas. This protein is thought to be involved in the control of fibroblast growth or epithelial-mesenchymal interactions during development, tissue repair, and epithelial carcinogenesis.