Arimidex Beats Tamoxifen in Keeping Breast Cancer at Bay

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Tamoxifen, which has been the gold standard of care in breast cancer treatment for more than 20 years, hinders the tumor's ability to use estrogen. Because Arimidex does not interfere with ovarian function, tamoxifen should still be used by premenopausal women with active ovaries, Buzdar said.

The first major results from ATAC, reported in 2001, found that Arimidex was more effective than tamoxifen in preventing a breast cancer recurrence and was better tolerated.

Subsequent data continued to show positive results.

The current data represent five years of active treatment plus three additional years of follow-up. In all, more than 9,000 women in 21 countries were involved in the study.

All the women had early-stage disease and had undergone surgery with or without chemotherapy and/or radiation. Eighty-four percent of participants had hormone-receptor-positive tumors.

The women were randomized to receive Arimidex alone or tamoxifen alone (a third arm involving a combination therapy had been halted earlier).

At the time of this 100-month follow-up, the mean age of participants was 72 years.

Arimidex improved disease-free survival by 15 percent compared with tamoxifen in women with hormone-receptor-positive breast cancer. The drug reduced the risk of all recurrences by 24 percent.

The improvement persisted even after treatment was stopped.

"The other question which was in all of our minds was what happens after you stop the pill," Buzdar said. "The pill was stopped three years ago, and the effect continues to be there. Even after stopping therapy, there are fewer recurrences in people who took Arimidex in the past."

The most common side effects were joint pain and estrogen deprivation leading to osteoporosis. Once the pill was stopped, however, a woman's risk of developing osteoporosis returned to normal. No new side effects were seen.

"Not only are you keeping more patients alive free of disease, but the safety profile is much more predictable and much more favorable than tamoxifen," Buzdar said.

More information

There's more on aromatase inhibitors at the U.S. National Cancer Institute.