The authors looked back at the cases of 1,325 women, almost all postmenopausal, who had been diagnosed with estrogen-receptor-positive, early-stage breast cancer.
Women were tested for CYP2D6 variants and divided into three groups based on the results: extensive metabolizers, extensive/intermediate metabolizers or poor metabolizers.
After an average follow-up of 6.3 years, women who were better metabolizers of CYP2D6 were less likely to see their cancer recur: 14.9 percent versus 20.9 percent in the intermediate group and 29 percent in the poor-metabolizer group. Low metabolizers also had lower rates of event-free survival, but no difference in overall survival. The authors did point out that the follow-up period was not long enough to actually determine differences in overall survival.
One expert had a mixed response to the new findings.
"I think this is real. I think these variants have some impact on how effective tamoxifen is for a given woman, but I don't think it's an all or nothing, either you respond or you don't. I think there are gradations of response," said Dr. Mary Daly, senior vice president of population science and director of the Cancer Prevention and Control Program at Fox Chase Cancer Center in Philadelphia.
But she also said she would like to see prospective studies before changing how she practices medicine.
"I'm not too sure how important this will be clinically because we're all sort of switching to aromatase inhibitors anyway," she added. "In general, though, it signals a movement towards personalizing therapies to genetic variants."
For his part, Jordan predicts that using genetic testing to help determine treatmen
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