Menopausal women with early breast cancer fare better if they are treated with Femara than if they are given the standard hormone therapy, tamoxifen, researchers report.

Woman treated for breast cancer who were given Femara were less likely to die or have their cancer come back, compared with those who were given tamoxifen, says Beat J. Thurlimann, MD, senior lecturer in medical oncology at the University of Basel in Switzerland.

The new study was presented at the annual American Society of Clinical Oncology.

Cancer was also less likely to spread to other parts of the body if a woman took Femara, he tells WebMD.

"We were particularly impressed by the additional protection of Femara in preventing distant recurrence -- that is, cancer spreading outside the area of the original tumor," he says. "That's the type of recurrence most feared by women and their doctors because it will ultimately lead to death."

Fighting Breast Cancer

About 70 percent of women with breast cancer have tumors that are fueled by estrogen.

Hormone therapy is a cornerstone of treatment to prevent recurrences and improve survival in women treated for breast cancer.

For over 25 years, doctors have been using tamoxifen, which binds to estrogen receptors and deprives breast cancer cells of the estrogen they need to grow. In contrast, Femara is part of a class of cancer-fighting drugs known as aromatase inhibitors that work by suppressing estrogen production in the body. Other aromatase inhibitors include Arimidex and Aromasin.

The new studies show that these differences in how the drugs work may mean that aromatase inhibitors may shrink tumors better, and with fewer side effects, say doctors not involved with the research.

Roy S. Herbst, MD, PhD, associate professor of medicine and cancer biology at the University of Texas M.D. Anderson Cancer Center in Houston, says, "The study confirms that an aromatase inhibitor should be the treatment of choice for postmenopausal women with early, estrogen-fueled breast cancer."

Herman E. Kattlove, MD, an American Cancer Society spokesman in Los Angeles, agrees. "We now know that aromatase inhibitors are more effective than tamoxifen at reducing breast cancer recurrence."

Femara's Fight Against Breast Cancer

The new study involved 8,028 postmenopausal women who were given either tamoxifen or Femara after breast cancer surgery.

More than two years later, Femara was shown to be better than tamoxifen on almost every measure. Femara lowered the risk of breast cancer recurrence or death caused by breast cancer by 19 percent compared with tamoxifen, and it reduced the risk of cancer spreading outside the area of the original tumor by 27 percent.

A total of 192 women on tamoxifen died, compared with 166 on Femara, Thurlimann says.

Side Effects Seen With Both Drugs

Both drugs were generally well tolerated, he says. While tamoxifen is effective against breast cancer, because it works against the effects of estrogen in breast tissue, it can have estrogen-like activity in the uterus and increase the risk of vaginal bleeding and endometrial cancer.

In the study, Femara cut in half the risk of vaginal bleeding, he says. About four times the number of women on tamoxifen needed biopsies to evaluate vaginal bleeding, which may be a sign of cancer to the lining of the uterus, he says.

Also, more women on tamoxifen suffered clots in the legs or lungs, Thurlimann says. Tamoxifen's estrogen-like effect is also known to increase the risk of blood clots.

But women taking Femara were more prone to joint pain, bone fractures, and slightly elevated cholesterol levels than those taking tamoxifen, he says.

Fatal strokes and heart attacks, while very rare, were also more common with Femara.

So What Should Women Be Doing for Breast Cancer?

That depends on the woman, Thurlimann says. "You can't extrapolate data from a clinical trial to an individual patient," he says.

While aromatase inhibitors have the edge over tamoxifen, "you have to take into account her risk of recurrence, her preferences, and her risk for side effects," he says. "For example, a woman with osteoporosis wouldn't be a good candidate for Femara."

Also, doctors still have to learn how to best use the aromatase inhibitors. Some studies show these drugs work best right after breast cancer surgery. Other studies indicate women could cut their risk of recurrence by taking an aromatase inhibitor after they've completed about five years on tamoxifen. Five years of tamoxifen is the standard treatment for menopausal women with estrogen sensitive tumors, after breast cancer surgery.

"What's clear is that tamoxifen alone is not the answer," Kattlove says. "Whether the best strategy is tamoxifen followed by an aromatase inhibitor, an aromatase inhibitor followed by tamoxifen, or an aromatase inhibitor alone is the big question."

A second part of the trial should offer answers to that question by 2008, Thurlimann says.

By Charlene Laino, reviewed by Brunilda Nazario, MD

SOURCES: 41st Annual Meeting of the American Society of Clinical Oncology, Orlando, Fla., May 13-17, 2005. Beat J. Thurlimann, MD, senior lecturer, medical oncology, University of Basel, Switzerland. Roy S. Herbst, MD, PhD, associate professor of medicine and cancer biology, University of Texas M.D. Anderson Cancer Center, Houston. Herman E. Kattlove, MD, American Cancer Society spokesman, Los Angeles.