FRIDAY, Dec. 14 (HealthDay News) -- The aromatase inhibitor drug Arimidex continues to outpace the old standard tamoxifen when it comes to preventing recurrences of hormone-receptor-positive breast cancers in postmenopausal women.

Even three years after treatment was stopped, women taking Arimidex still saw a benefit, researchers said.

"It has been very good news," said Dr. Aman Buzdar, U.S. principal investigator of the ATAC (Arimidex or Tamoxifen Alone or in Combination) trial, the results of which were expected to be presented Friday at the 2007 San Antonio Breast Cancer Symposium.

"A lot more women receiving Arimidex are free of cancer compared to tamoxifen, and the 100-month data show that these differences, if anything, with time actually continued to increase -- meaning there were fewer and fewer recurrences on Arimidex compared with tamoxifen," Buzdar said.

"Arimidex is the standard of care for postmenopausal women with receptor-positive breast cancer," confirmed Dr. Jay Brooks, chairman of hematology/oncology at Ochsner Health System in Baton Rouge, La. "One hundred months [over eight years] of follow-up is very profound. It's a true credit to the investigators to be able to do the study and have that much follow-up, and it shows that we have reached a new level of care for postmenopausal women. That's what I use and continue to use."

Hormone-receptor-positive cancers respond to circulating estrogen or progesterone. Experts estimate that from 50 percent to 70 percent of breast cancers are hormone receptor positive.

The new findings were also expected to be published in the journal The Lancet Oncology to coincide with the presentation.

Arimidex (anastrozole) is an aromatase inhibitor, a relatively new class of compounds that blocks estrogen production in the body. According to Buzdar, who is professor of medicine and deputy chair of the department of breast medical oncology at the University of Texas M.D. Anderson Cancer Center, Arimidex is now indicated for postmenopausal women who have a hormone-dependent cancer.

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.

SOURCES: Aman Buzdar, M.D., professor, medicine and deputy chair, department of breast medical oncology, University of Texas M.D. Anderson Cancer Center, Houston; Jay Brooks, M.D., chairman, hematology/oncology, Ochsner Health System, Baton Rouge, La.; Dec. 14, 2007, presentation, 2007 San Antonio Breast Cancer Symposium

Copyright © 2007 ScoutNews, LLC. All rights reserved.