CYP2D6 genotype affects outcome in postmenopausal breast cancer patients treated with tamoxifen monotherapy

Tamoxifen efficacy may be influenced by a number of factors, including CYP2D6 genotype, co-administration of drugs that inhibit CYP2D6, and adherence to tamoxifen therapy. CYP2D6 plays a major role in catalyzing the conversion of tamoxifen to its active metabolite endoxifen. Studies of the relevance of CYP2D6 genotyping have had conflicting results due to various limitations: differences in CYP2D6 allele coverage, phenotype classification and other confounding variables.