FRIDAY, Dec. 28 (HealthDay News) For breast cancer patients prescribed tamoxifen to treat their disease, genetic traits affecting an enzyme in the liver are major players in determining the impact of the hormone therapy, new research suggests.
There's been debate in the scientific world for years over the role of genetic differences in the enzyme, known as CYP2D6. An estimated 5 percent to 7 percent of European and North American women have a trait that prevents the enzyme from working properly.
"Our findings confirm that, in early breast cancer treated with tamoxifen, genetic alterations in CYP2D6 lead to a higher likelihood of recurrence and death," Dr. Matthew Goetz, a Mayo Clinic oncologist and lead author of the study that reported the findings, said in a Mayo Clinic news release.
The researchers tracked two groups of women: postmenopausal women with primary estrogen receptor-positive breast cancer who received tamoxifen for five years, and those took got the drug for two years followed by another drug, anastrozole, for three years.
Among those who took tamoxifen for five years, those whose genetic makeup prevented the enzyme from being able to process things were 2.5 times more likely to die or have their cancer return than those whose enzymes worked normally, the investigators found.
However, genetic traits involving the enzyme didn't seem to influence the fates of the women who switched to anastrozole, an aromatase inhibitor, after two years of tamoxifen, the study found.
"Switching from tamoxifen to an aromatase inhibitor may be one reason for the discrepant studies surrounding CYP2D6 and tamoxifen -- as information about whether a patient took an aromatase inhibitor after tamoxifen was not available in most of the prior studies," senior author Dr. James Ingle, of the Mayo Clinic, said in the news release.
Goezt thinks the study findings confirm that women should switch from tamoxifen to an aromatase inhibitor, or avoid tamoxifen altogether, if tests show they have the genetic trait that limits the metabolizing process.
The study was released online in advance of publication in an upcoming print issue of the journal Clinical Cancer Research.
For more about breast cancer, visit the U.S. National Library of Medicine.
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