Cytochrome P450 (CYP) 1A1 hydroxylates E1 and E2 preferentially at the 2-position, whereas CYP1B1 hydroxylates almost exclusively at the 4-position2-4, and the 4-OHE1(E2) are the most important metabolites in cancer initiation (Figure 1)5-7. This evidence concerns the gene CYP1B1 and cancer.