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Breast Cancer Health Center

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Tamoxifen Benefit Even After Therapy

Pill Continues to Prevent Breast Cancer, With Fewer Side Effects
WebMD Health News
Reviewed by Louise Chang, MD

Dec. 19, 2006 (San Antonio) -- Tamoxifen cuts the risk of breast cancerin some women by about a third, a new study confirms, and the benefit persists even after treatment ends.

Meanwhile, "many serious side effects that were apparent during active treatment disappeared over time," says researcher Jack Cuzick, MD, of Cancer Research UK in London.

Initial results of the trial, released in 2002, showed that five years of tamoxifen therapy prevents the type of breast cancer that needs estrogen to grow.

These new results provide "the clearest evidence to date that you get benefit even after stopping tamoxifen," says Powell Brown, MD, PhD, a breast cancer specialist at Baylor College of Medicine in Houston.

Brown, who was not involved with the study, moderated the session where the research was presented at the 29th Annual San Antonio Breast Cancer Symposium.

Tamoxifen and Breast Cancer Risk

The study looked at 7,145 women at high risk of developing breast cancer because they had either a mother or a sister who developed the disease before age 50, other family history of breast cancer, or a previous noncancerous breast tumor.

The women took either a tamoxifen pill or a placebo for a period of five years between 1992 and 2001.

By a median eight years later, 87 women on tamoxifen vs. 129 women on the placebo had developed cancers fueled by estrogen.

Those numbers translate to a 34% reduction in risk for the women on tamoxifen.

"More than 10 years out, the risk reduction is quite consistent with what we saw at five years," Cuzick says.

Tamoxifen did not help prevent the type of tumors not fueled by estrogen, which are notoriously difficult to treat, he says.

Also, while many doctors had thought tamoxifen could prevent breast cancer in women taking hormone replacement therapy (HRT), that did not prove to be the case.

"The data do not support the hypothesis that you can prevent HRT-related breast cancers by giving tamoxifen," he tells WebMD.

Tamoxifen Side Effects Dissipate

Cuzick says many common side effects -- including headaches, abnormal bleeding, and hot flashes -- virtually disappeared after stopping tamoxifen.

Tamoxifen is also known to cause potentially dangerous blood clots. However, by a median eight years after stopping treatment, women on tamoxifen were no more likely to have clots than those on a placebo.

Similarly, tamoxifen increased the risk of uterine cancer during active treatment. But after stopping therapy, women who had taken tamoxifen were slightly less likely to develop uterine cancer than those on placebo.

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