Notes: (E/Z)-Endoxifen is a mixture of (E)-endoxifen and (Z)-endoxifen.{29622} (Z)-Endoxifen is an active metabolite of the estrogen receptor antagonist tamoxifen (Item Nos. 13258 / 11629) and is formed from tamoxifen primarily by the cytochrome P450 (CYP) isoform CYP2D6 via an N-desmethyltamoxifen (Item No. 40673) intermediate.{28446} (Z)-Endoxifen (100 nM) inhibits 17β-estradiol-induced increases in mRNA encoding the progesterone receptor in MCF-7 breast cancer cells.{67256} (E)-Endoxifen is a potential impurity in commercial preparations of (Z)-endoxifen.{72413}