Fibroblast growth factor receptor 4 is a protein that in humans is encoded by the FGFR4 gene. FGFR4 has also been designated as CD334 (cluster of differentiation 334). The protein is a member of the fibroblast growth factor receptor family, where amino acid sequence is highly conserved between members and throughout evolution. A full-length representative protein would consist of an extracellular region, composed of three immunoglobulin-like domains, a single hydrophobic membrane-spanning segment and a cytoplasmic tyrosine kinase domain. The extracellular portion of the protein interacts with fibroblast growth factors, setting in motion a cascade of downstream signals, ultimately influencing mitogenesis and differentiation. This particular family member preferentially binds acidic fibroblast growth factor and, although its specific function is unknown, it is overexpressed in gynecological tumor samples, suggesting a role in breast and ovarian tumorigenesis. In a meta-analisis study, the functional polymorphism Gly388Arg (rs351855) of FGFR4 was observed to be significantly associated with nodal involvement and overall survival in patients with different types of cancer.