Fibroblast growth factor 8b （FGF-8b）, a secreted heparin-binding protein, is a member of the fibroblast growth factor （FGF） family and is an isoform of FGF-8. Alternative splicing of fgf-8 gene gives rise to potentially four （a, b, e, f） different protein isoforms in human, and FGF-8b exhibits the highest transforming activity in NIH3T3 cells. FGF-8b signals through FGF receptors （FGFRs） to activate PI3K and MAPK pathways. FGF-8b is broadly associated with mitogenic and cell survival activities, and regulates gastrulation, epithelial-mesenchymal transition, and later on mesenchymal to epithelial differentiation during embryonic development. FGF-8b has also been found in peripheral blood leukocytes and healthy bone marrow samples.