Endoxifen levels and metabolic phenotype-associated factors in Mexican Mestizo patients under tamoxifen treatment.

Abstract

Aim: To evaluate plasma endoxifen levels and metabolic phenotype-associated factors in Mexican Mestizo patients under tamoxifen treatment. Patients & methods: A total of138 breast cancer patients under tamoxifen treatment were cross-sectionally evaluated andside effects (SE) were recorded. CYP2D6 genetic phenotypes (GP) and metabolic phenotypes (MP)were assessed(metabolic poor [mPM], intermediate [mIM], normal [mNM], and ultrarapid [mUM] metabolizer). Associations were tested in uni-multivariate models for endoxifen >5.9ng/ml and for mNM+ mUMMP. Results: The main SE was hot flashes (62%). Distribution of the CYP2D6MP was 4.3%mPM; 14.5% mIM; 75.4% mNM;and 5.8% mUM. Endoxifen >5.9ng/ml was partially associated with SE (p = 0.06); the mNM+ mUM MP was associated with treatment time (p = 0.03). Conclusion: The endoxifen-associated factors in Mexican Mestizo patients remain inconclusive, although treatment time was associated with MP.