The newest family of breast cancer drugs is ready for prime time, a major cancer organization now says.

The new drugs are Arimidex, Aromasin, and Femara. Doctors call them third-generation aromatase inhibitors (search). For increasing numbers of postmenopausal breast cancer patients, they're taking the place of tamoxifen (search) for after-surgery treatment.

Until now, the American Society for Clinical Oncology (ASCO) has recommended tamoxifen to reduce the risk of recurrent breast cancer after surgery. Now, an ASCO blue-ribbon panel says doctors may also choose Arimidex, Aromasin, or Femara.

Like tamoxifen, the new breast cancer drugs are for postmenopausal women only. They are used after breast cancer surgery to prevent breast cancer from coming back. The drugs keep the body from making the sex hormone estrogen, which makes many breast cancers grow faster. Therefore, the drugs are useful only in women with hormone-sensitive breast cancers.

ASCO's new guidelines say postmenopausal women should consider after-surgery treatment with aromatase inhibitors:

—If their breast cancers tested positive for hormone receptors

—If they cannot take tamoxifen

—If they already have taken tamoxifen for two to three years, or for five years

The guidelines — released today — will appear in the Jan. 20, 2005 issue of the Journal of Clinical Oncology.

Lower Recurrent Breast Cancer, Side Effect Risk

The new breast cancer drugs work better than tamoxifen — and they have less dangerous side effects, says Aman Buzdar, MD, deputy chair of the department of breast and medical oncology at University of Texas M.D. Anderson Cancer Center.

"All new postmenopausal breast cancer patients should be offered aromatase inhibitors," Buzdar tells WebMD. "The evidence suggests they lower the risk of breast cancer recurrence, and they have lower-risk side effects."

In studies, Arimidex, Aromasin, and Femara carry a lower risk of potentially deadly blood clots and uterine cancer than tamoxifen. However, the breast cancer drugs do increase the risk of bone loss and fracture — a major concern for women after menopause. Buzdar says this risk can be minimized by bone-loss-preventing drugs.

And risk is the name of the game, says breast cancer specialist Pamela N. Munster, MD, of H. Lee Moffitt Cancer Center, Tampa, Fla.

"Any benefit of [post-surgery] breast cancer chemotherapy is a matter of risk reduction," Munster tells WebMD. "The higher a woman's risk, the more the benefit. First, we need to know if a patient needs chemotherapy. If a woman has a hormone-sensitive tumor, the choice becomes which treatment to use. So since the aromatase inhibitors seem better, most doctors would use them first."

Are Arimidex, Aromasin, and Femara interchangeable? Nobody knows yet. It will be years before definitive information is available. Munster says doctors now have to make their decisions based on limited evidence.

"Based on the information that is out there, if a patient came to me to get started, I would use Arimidex," Munster says. "If the patient has been on tamoxifen for two to three years, I would use Aromasin. But if she were on tamoxifen for five years, I would switch her to Femara."

Some doctors, Buzdar says, think there may be a long-term benefit to starting with tamoxifen, then switching to one of the new breast cancer drugs. But he believes the new drugs offer a woman her best chance of remaining cancer-free after surgery.

"The most important thing breast cancer patients should ask their doctors is why they are on tamoxifen and not on aromatase inhibitors," Buzdar says.

But there still are very good reasons to start with tamoxifen, says Carl Kardinal, MD, director of clinical research at the Ochsner Clinic Foundation in New Orleans.

"Tamoxifen has been around for more than 30 years. We know the side effects. The newer aromatase drugs, we don't really know yet," Kardinal tells WebMD. "Another issue which is very important is the cost. Tamoxifen is now available as a generic drug, and costs in the range of $40-$45 a month. Aromatase inhibitors like Arimidex and Femara cost more than $200 a month."

By Dan DeNoon, reviewed by Brunilda Nazario, MD

SOURCES: Winer, E.P. Journal of Clinical Oncology, Jan. 20, 2005; vol 23. News release, American Society for Clinical Oncology. ASCO web site. Aman Buzdar, MD, professor of medicine and deputy chair of the department of breast and medical oncology, University of Texas M.D. Anderson Cancer Center, Houston. Pamela N. Munster, MD, assistant professor H. Lee Moffitt Cancer Center, University of South Florida, Tampa. Carl Kardinal, MD, director, clinical research, Ochsner Clinic Foundation, New Orleans.