Fetuin-B is a member of the Fetuin family that is part of the Cystatin superfamily of Cysteine Protease inhibitors. It is reported that Fetuin-B is highly expressed in liver tissue, in tongue and placenta tissues. Fetuin-B is a paralogue of Fetuin-A. Fetuin-A and Fetuin-B display similarities and differences in their characteristics, however, they share only 20% amino acid sequence identity. The amounts of Fetuin-B in human serum, unlike Fetuin-A, vary with gender and are higher in females than in males. Fetuin-B is an inhibitor of basic calcium phosphate precipitation but is less active than Fetuin-A. Fetuin-B expression is decreased in Fetuin-A deficient knock-out mice. The expression of Fetuin-B has been shown to be regulated by FXR (Farnesoid X Receptor), a nuclear receptor activated by bile acids. Evidence has shown that overexpression of Fetuin-B in skin squamous carcinoma cells suppresses tumor growth in nude mice. The function of Fetuin B is still not fully characterized.