Individualization of tamoxifen treatment for breast carcinoma.

Traditionally, all patients treated with tamoxifen receive a standard dose. A number of studies claimed a clinically relevant impact of cytochrome P450 2D6 (CYP2D6) genotype on outcome, and therefore genotyping before tamoxifen therapy was advocated. Recent data showed that adequate exposure to the active metabolite endoxifen is important and that genotype only partially explains interindividual differences in endoxifen concentrations. Phenotyping approaches, as well as therapeutic drug monitoring (TDM) strategies, are now being tested to individualize tamoxifen treatment.