Figure 1.

Plasma tamoxifen, endoxifen, 4-hydroxy (4-OH) tamoxifen, and N-desmethyl tamoxifen levels in women with estrogen receptor-positive breast cancer receiving adjuvant tamoxifen (20 mg/day) for 4 months. Data are expressed as means ± standard error of the mean. Panel A shows the significant difference (P <0.001) in 4-OH tamoxifen and endoxifen between extensive and poor CYP2D6 metabolizers (black bars = extensive metabolizers, white bars= intermediate metabolizers, grey bars = poor metabolizers). Panel B depicts tamoxifen and N-desmethyl tamoxifen levels in extensive, intermediate, and poor CYP2D6 metabolizers (non-significant difference) (black bars = extensive metabolizers, white bars= intermediate metabolizers, grey bars = poor metabolizers).