Mammalian alkaline phosphatases (APs) are highly conserved zinc-containing allosteric enzymes that are able to hydrolyze and transphosphorylate a wide range of compounds. There are four known human alkaline phosphatase isozymes: TNAP (tissue-nonspecific; bone/liver/kidney), ALPP (placental), ALPP2 (germ cell), and ALPI (intestinal). Placental alkaline phosphatase (ALPP) is bound to the plasma membrane via a glycosyl-phosphatidylinositol (GPI) anchor. It is expressed primarily in the placenta and may be involved in transplacental IgG transport. ALPP has been found to be overexpressed on the surface of several different types of solid tumor cells and elevated serum concentrations of ALPP and ALPP-like enzymes has been found to be associated with ovarian, cervical, and testicular cancer.