Schematic of simplified estrogen metabolism. Estrone (E1) and estradiol (E2) can be metabolized through oxidation pathways by cytochrome P450 (CYP) 1A, 1B, and 3A producing 2-, 4- and 16α-hydroxyestrogen (2-OHE, 4-OHE and 16α-OHE, respectively). 2-OHE and 4-OHE derivatives can be further converted to 2- and 4-methoxyestrogen metabolites (2-MeOE and 4-MeOE, respectively), which can have beneficial, antiproliferative properties. 16α-OHE, on the other hand, exerts proproliferative effects.