Another Reason Not to Test for CYP2D6

The CYP2D6 enzyme metabolizes tamoxifen to its active metabolite endoxifen. Earlier small studies have suggested that genotyping could categorize patients as extensive, intermediate, or poor metabolizers of tamoxifen. By extension, the hypothesis was that patients would derive different benefits from tamoxifen depending on their ability to metabolize it. However, multiple studies analyzing tumor tissue and clinical outcomes from large adjuvant endocrine trials have come to differing conclusions. As a result, practice guidelines do not recommend that CYP2D6 testing be used to make treatment decisions.

Now, investigators have identified another technical problem that potentially undermines the ability to classify CYP2D6 status accurately. Prev…