By Amanda Gardner
HealthDay Reporter

(HealthDayNews) -- A group of drugs called aromatase inhibitors should be used after surgery to treat postmenopausal women with hormone-receptor-positive breast cancer, new guidelines recommend.

The guidelines are an updated technology assessment from the American Society of Clinical Oncology (ASCO), and they appear in the Nov. 15 issue of the Journal of Clinical Oncology.

This is first time ASCO has recommended that this class of drugs be used in this group of women.

"We've done this yearly for the past three years," said Dr. Eric Winer, lead author of the technology assessment and director of the Breast Oncology Center at Dana Farber Cancer Institute in Boston. "The difference this year was that, in our minds, there was enough data for us to say that in a woman who is postmenopausal at diagnosis and who has hormone-receptor-positive breast cancer, that the very best hormonal therapy includes an aromatase inhibitor at some point in time for most women."

Dr. Jay Brooks, chief of hematology/oncology at the Ochsner Clinic Foundation in New Orleans, said the new guidelines "show the continued progress that good solid clinical research does. I'm very encouraged and I think it will be an important advance in the treatment of women who are postmenopausal."

Like tamoxifen, aromatase inhibitors work by decreasing the amount of circulating estrogen in the body. Tamoxifen has dominated the breast-cancer treatment landscape for more than 20 years. This new class of drugs, three of which have been approved by the U.S. Food and Drug Administration, represents the first real challenge to tamoxifen's reign.

"Over the past 20 years, the use of tamoxifen has revolutionized the prevention and treatment of breast cancer," Brooks said. "This is a next step. I think this will eventually replace tamoxifen in postmenopausal women."

Previous trials had shown promise with the aromatase inhibitor called anastrozole (Arimidex). As a result, previous ASCO recommendations had singled out this drug.

Three new randomized trials have shown encouraging results for two other aromatase inhibitors as well. Those drugs are letrozole (Femara) and exemestane (Aromasin). All three drugs are approved by the U.S. Food and Drug Administration.

Based on results from these clinical trials, the new ASCO recommendations state that doctors and patients can substitute one of the three FDA-approved aromatase inhibitors for tamoxifen as the initial adjuvant (after surgery) therapy. Women can also choose to start with tamoxifen, then switch to an aromatase inhibitor after two to five years. A woman who switches to an aromatase inhibitor after tamoxifen should take the aromatase inhibitor from two to three years but no longer than five years because there is no clinical data longer than that. There's also no data on taking tamoxifen after an aromatase inhibitor, the guidelines state.

Although only one study showed a survival advantage associated with an aromatase inhibitor, the technical assessment pointed to "clear and consistent" improvement in disease-free survival for women receiving an aromatase inhibitor, ASCO said.

It's not yet clear to researchers whether women would be better served by taking aromatase inhibitors in place of tamoxifen or in addition to it.

"We don't know the answer to that," Winer said. "The big challenge is sorting that out. It is reasonably likely that there won't be one single strategy for all women and that there will be differences based on different tumors and different women who may be at risk for different sets of complications."

"Breast cancer is more and more a disease that we're recognizing as not one disease but many different diseases occurring that really need to be treated in something other than a one-size-fits-all manner," he added.

Many questions remain to be answered, notably what are the long-term effects of aromatase inhibitors. There is some evidence they may reduce the risk of blood clots and uterine cancer but may increase the risk of osteoporosis and fractures, the ASCO recommendations state.

"We don't have 20-year follow-up data," Winer pointed out. "We've learned a little bit of a lesson from Vioxx [an arthritis pain drug recently pulled from the market because it can cause heart attack and stroke]. And tamoxifen is a drug that we do have 30-year follow-up data for. Anytime we have a new drug and it's replacing an old drug that we're very comfortable with, you just have to have a little bit more caution."

SOURCES: Eric P. Winer, M.D., director, Breast Oncology Center, Dana Farber Cancer Institute, Boston; Jay Brooks, M.D., chief, hematology/oncology, Ochsner Clinic Foundation, New Orleans; Nov. 15, 2004, Journal of Clinical Oncology