New Breast Cancer Drugs Dramatically Advance Treatment for Older Women

A new family of drugs known as aromatase inhibitors is more effective at treating breast cancer in older women than the current gold-standard drug, tamoxifen, researchers said Wednesday.

The drugs also reduced recurrence of the disease and eliminated the most severe side effects associated with breast cancer treatment.

An international study on more than 9,000 women with localized breast cancer showed that one of the drugs, anastrozole, raised disease-free survival by 10%, increased the time to recurrence by 20% and reduced spread of the cancer to the second breast by 40%, compared with tamoxifen.

Trade-named Arimidex, anastrozole should be the first choice in treating as many as half of the 213,000 American women who develop breast cancer each year, said Dr. Aman Buzdar of the University of Texas M.D. Anderson Cancer Center in Houston, a coauthor of the study.

“Arimidex is a much better drug,” he said. “I see little reason to use tamoxifen as the initial treatment in new patients with breast cancer.”

Buzdar presented data from the study at the San Antonio Breast Cancer Symposium on Wednesday, and the research was simultaneously published online in the international medical journal Lancet.

A second study presented at the symposium showed that switching to another member of the family, exemstane (trade named Aromasin), after two years of tamoxifen therapy was substantially more effective than sticking to tamoxifen for the normal five-year course of therapy.

The study of nearly 5,000 patients showed that women who switched to exemstane after two years had a 30% reduction in recurrence over the three years of the study and a 54% reduction in cancer in the second breast, according to Dr. Charles Coombes of Imperial College London.

The benefit of exemstane “justifies offering treatment as early as possible,” Coombes said.

A third study of more than 3,000 women showed that switching from tamoxifen to anastrozole after two or three years reduced the risk of recurrence by 40%.

They are powerful drugs, said Dr. Derek Raghavan of the Cleveland Clinic, who was not involved in the studies.

“You don’t have to be a rocket scientist to see that there are consistent improvements,” he said.

“People forget that tamoxifen already cuts recurrence of cancer by 50%.”

Using one of the new drugs could reduce it by 70% to 80%, Raghavan said.

Because the three studies examined different patient populations and different drugs, a direct comparison of the percentage changes is not possible.

What is clear is that the aromatase inhibitors are generally more effective than tamoxifen, and that using them earlier in the treatment process produces greater benefits.

Tamoxifen revolutionized breast cancer treatment when it was introduced three decades ago.

It prevents a woman’s estrogen from binding to cancer tissues and promoting their growth.

About 75% of postmenopausal breast cancer patients and about 20% of premenopausal ones have tumors sensitive to estrogen.

But tamoxifen can have severe side effects, including the development of endometrial cancer, exacerbating blood clotting and producing vaginal bleeding and discharge.

The aromatase inhibitors, approved for sale about three years ago, work by a completely different mechanism, blocking the body’s production of estrogen and thereby robbing tumors of their stimulation.

So far, they do not seem to produce the side effects caused by tamoxifen, although they can decrease bone density, leading to joint pain and fractures, which can be treated with other drugs.

Results reported last year with a third member of the family of drugs, lotrezole (trade named Femara), showed that giving it to women after they had completed five years of therapy with tamoxifen -- at which point that drug is no longer effective -- could reduce tumor recurrence over the next five years by 43%.