The changes in 2007 suggesting pharmacogenomic testing didn't go far enough, evidently, so now, with pretty minimal evidence, FDA has gone ahead and upped the ante with specific recommendations for starting doses depending on the VKORC polymorphism profile. They cite "multiple studies" to justify a dosing table (!), which is news to me.
The 1960s brought flower power and also the invention of Tamoxifen. Tamoxifen reduced breast cancer recurrence by 50%, and women everywhere rejoiced.
Does the evidence support routinely testing patients for CYP2D6 polymorphisms if they are planned for tamoxifen treatment? We know that "poor metabolizers" include those with certain characteristic polymorphisms in the CYP2D6 gene. We now have commercially available testing to profile patients in advance of planned tamoxifen use and clinicians are starting to ask whether such testing is routinely indicated.