Fibroblast growth factor 9 (FGF-9), also known as heparin-binding growth factor 9 (HBGF-9), belongs to the FGF family. FGF-9 binds several FGF receptors, FGFR 1c, 2c, 3b, 3c, and 4, and similarly to all FGF members, plays a crucial a role as cell mitogen and regulator of cell differentiation. In the nervous system, FGF-9 is secreted by neurons and induces survival signals for glial cells and astrocytes. During embryogenesis FGF-9 is a key factor for gonad development and determination of sexual phenotype, as well as skeletal development. FGF-9 is also expressed by prostatic and brain cancer.