摘要：

To the Editor: Irvin et al1 for the first time provided evidence for the feasibility of CYP2D6 genotype-guided tamoxifen dosing. Doubling of the daily dose of 20 mg/d tamoxifen to 40 mg/d led to a significant rise in endoxifen concentrations in intermediate metabo-lizers and poor metabolizers (PMs). Intermediate metabolizers but not PMs reached endoxifen levels comparable to those of extensive metabolizers (EMs) with normal tamoxifen dose.

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