FGF-8 belongs to the fibroblast growth factor (FGF) family and plays an important role in cell growth, embryogenesis, and tumorigenesis. Four isoforms (a, b, e, and f) of human FGF-8 generated by alternative splicing of the mRNA have been described. The isoforms may have different functions during embryogenesis. During prenatal stages, FGF-8 is required for the normal development of various organs, including limbs and central nervous system. FGF-8 was first cloned from SC-3 mouse mammary carcinoma cells and was found to be induced in response to androgenic stimuli. FGF-8 is found to have a transforming capacity and is detected in human prostate and breast carcinoma specimens and cell lines. The isoform FGF-8b has the highest affinity to FGF receptors and the strongest transforming capacity.