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Breast Cancer: Arimidex vs. Tamoxifen

Study Shows Arimidex Beats Tamoxifen for Prevention of Cancer Recurrence
WebMD Health News

Dec. 14, 2007 (San Antonio) -- Even after treatment ends, Arimidex beats out tamoxifen in preventing breast cancer recurrence in women with hormone-fueled tumors.

Updated results from this landmark trial also show that the increased risk of fractures associated with Arimidex therapy disappears after treatment stops.

In the study, more than 5,000 women with hormone-receptor-positive tumors were followed for more than three years after treatment was stopped. The researchers show that an additional 25% of recurrences were prevented by Arimidex, compared with tamoxifen, says John F. Forbes, MD, professor of surgery at the University of Newcastle in Australia.

During treatment, nearly 3% of women taking Arimidex had bone fractures vs. only 2% on tamoxifen. More than three years after treatment ended, the percentage was about 1.5% in both groups.

Forbes reported the findings here at the annual San Antonio Breast Cancer Symposium. Results of the study, which was funded by AstraZeneca, maker of Arimidex, were simultaneously published online in the journal Lancet Oncology.

'Carryover' Effect

Studies have shown that Arimidex is better at preventing relapses than tamoxifen during the five years that women are being treated with these drugs.

What we didn't know, Forbes says, is what would happen after women stop taking them.

"The news here is that the hoped-for carryover effect seems to be true," William Gradishar, MD, a breast cancer specialist at Northwestern University in Chicago, tells WebMD.

"The safety issue, particularly with regard to bone disease, is reassuring as well," says Gradishar, who was not involved with the work.

Arimidex and other aromatase inhibitors shut down the body's ability to make estrogen.

Tamoxifen blocks estrogen's effects, but not in the same way as Arimidex and its sister drugs Femara and Aromasin. Tamoxifen blocks estrogen from getting into cancer cells, slowing tumor growth.

Arimidex Cuts Breast Cancer Relapses

The landmark study involved postmenopausal women with early-stage breast cancer. They were given either tamoxifen or Arimidex for five years, following breast cancer surgery.

The new analysis followed only about 5,000 of these women who had hormone-receptor-positive tumors. These are the tumors that are targeted by the aromatase inhibitors such as Arimidex.

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