Platelet-derived growth factor receptors (PDGF-R) are cell surface tyrosine kinase receptors for members of the platelet-derived growth factor (PDGF) family. PDGF subunits -A and -B are important factors regulating cell proliferation, cellular differentiation, cell growth, development and many diseases including cancer.  There are two forms of the PDGF-R, alpha and beta each encoded by a different gene.  Depending on which growth factor is bound, PDGF-R homo- or heterodimerizes.