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By determining who would and would not receive possible benefit from two preventive drugs, women who aren't likely to respond could be spared the treatment and its side effects, the study authors noted.
The investigators found that women with a favorable genetic variation (called a "single nucleotide polymorphism" or SNP) in the gene ZNF423 and another near the gene CTSO were more likely to respond to prevention therapy with tamoxifen and raloxifene.
Women with unfavorable variations of these SNPs may not benefit from prevention therapy and have a five-fold increased risk of developing breast cancer, according to the study published June 13 in the journal Cancer Discovery.
"The recent guidelines by the U.S. Preventive Services Task Force emphasize that ... therapy with tamoxifen and raloxifene can lower a woman's risk for developing breast cancer. But about 50 women have to be exposed to the treatment and side effects to prevent a single case of breast cancer," study author Dr. James Ingle, a professor of oncology at the Mayo Clinic in Rochester, Minn., said in a journal news release.
"Our findings are important, because for the first time, we discovered genetic factors that could be used to select women who should be offered the drugs for prevention. Also of substantial importance is that we have discovered new information on how tamoxifen and raloxifene work to prevent breast cancer," he added.
"Findings from our study provide clear direction as to which women are likely and which are unlikely to benefit from tamoxifen or raloxifene," Ingle explained. "The best chance we have of decreasing the burden of breast cancer is to prevent it in the first place. Our findings provide the basis for a reinvigoration of research efforts in breast cancer prevention."
-- Robert Preidt
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SOURCE: Cancer Discovery, news release, June 13, 2013