e11501 Background: The clinical outcome of tamoxifen-treated breast cancer patients may be influenced by the activity of cytochrome P450 enzymes that catalyze the formation of antiestrogenic metabolites endoxifen and 4-hydroxytamoxifen. Methods: The AmpliChip CYP450 Test was used to identify CYP2D6 genotypes which have an impaired ability to metabolize tamoxifen into the active metabolite, endoxifen. Results: Our aim is to determine the share of ultrarapid (UM), extensive (EM), intermediate (IM) and poor (PM) metabolizers in the group of postmenopausal women with estrogen receptor-positive breast cancer. We are presenting first 72 results as the part of long term study on 180 women. It is evident that EM and UM have significantly lower percentage of disease progression (22% respectively 0%) compare to IM (67%). No progression observed at PM needs further monitoring and investigation. Conclusions: The results tentatively support the hypothesis, that the genetic variants associated with activity of CYP2D6 could help to clinicians in determining the therapeutic strategy. [Table: see text] No significant financial relationships to disclose.
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