Gene Predicts Tamoxifen Success in Breast Cancer

Oct. 8, 2009 -- A single gene variant predicts breast cancer survival after tamoxifen treatment, a new study finds.

In the 46% of women with the "good" gene, tamoxifen works as well as newer drugs. For women with the gene variant linked to poor response to tamoxifen treatment, other treatment strategies would be a better choice.

In the past 25 years, tamoxifen has prevented more than half a million deaths from breast cancer. The drug helps prevent breast cancer recurrence after surgery. Tamoxifen is still a useful drug, although newer drugs called aromatase inhibitors seem to work better in clinical trials.

Now it appears that some women will do at least as well if they're treated with tamoxifen. Such women carry a version of a gene called CYP2D6 that makes tamoxifen work better.

The gene encodes an enzyme crucial to tamoxifen activity. About 46% of women have a version of the gene that contributes to high enzyme activity. Others have genes that contribute to low or intermediate activity of the enzyme.

Werner Schroth, PhD, of Germany's Fischer-Bosch Institute of Clinical Pharmacology, and colleagues analyzed CYP2D6 genes in 1,325 postmenopausal women treated with tamoxifen for early-stage breast cancer in Germany and in the U.S.

They found that women with the highly active version of the gene were significantly less likely to have their breast cancer come back after five years of tamoxifen treatment. These women had outcomes similar to those seen in women treated with aromatase inhibitors.

"[This] should provide new impetus to the medical and scientific community to revisit the issue of the relative efficacy of these two approaches in women with early breast cancer," Schroth and colleagues conclude.

The researchers suggest that genetic testing could identify women who should not be treated with tamoxifen.

Schroth and colleagues report the findings in the Oct. 7 issue of TheJournal of the American Medical Association.