A newer drug called anastrozole could soon replace tamoxifen as the standard treatment for postmenopausal breast cancer patients whose cancer is fueled by estrogen, according to an international study.

Anastrozole (Arimidex) is one of a class of drugs called aromatase inhibitors and was significantly more effective than tamoxifen in a number of areas. More women taking anastrozole remained free of cancer than those taking tamoxifen. If cancer did recur, more time elapsed before the recurrence in patients taking anastrozole. In addition, anastrozole reduced the incidence of cancer spreading, particularly to the other breast.

The Study

The study included nearly 10,000 postmenopausal women who had localized breast 42 cancer—it had not spread to the lymph nodes or beyond—and had been treated with surgery.

The women were separated into three groups: those who took tamoxifen, those who took anastrozole, and those who took both drugs. The women were followed up for five years following their initial treatment. However, after three years, the group taking both drugs was disbanded because the treatment appeared to be not as effective.

The Results

After five years, researchers found that 10% more women taking anastrozole were disease-free compared with the women taking tamoxifen. The anastrozole group also had a 20% longer period of time until the cancer recurred and 400/o fewer instances of cancer spreading to the other breast than the group taking tamoxifen. In addition, the women taking anastrozole were 14% less likely to have their cancer spread to other sites in the body.

In addition, compliance rates were higher for those women taking anastrozole compared with tamoxifen perhaps because anastrozole produced fewer side effects, although bone fractures and joint pain were more common than among women given tamoxifen, the study found.

The study did not show any significant improvement in the overall survival rates among those women who took anastrozole compared with the women who took tamoxifen. However, more time is necessary to determine if anastrozole will produce better long-term survival rates.


The researchers found that prescribing anastrozole immediately after surgery significantly improved results for patients, and they recommend giving anastrozole instead of tamoxifen to women for five years following their initial cancer treatment.

Currently, postmenopausal women whose breast cancer is hormone-receptor-positive—approximately 75% of all patients—take tamoxifen for five years after breast cancer surgery. The drug blunts estrogen's ability to fuel cancer growth. In contrast, anastrozole prevents estrogen from being produced. It is often prescribed for women following tamoxifen therapy.

"Results from studies suggest that it is reasonable to switch patients currently on tamoxifen to an aromatase inhibitor," say the researchers. The study was led by Anthony Howell, a professor at Christie Hospital NHS Trust, in Manchester, England.

However, some cancer experts note that aromatase inhibitors can come with significant side effects, including an increased risk of osteoporosis.

Dr. Otis W. Brawley, professor of oncology at Emory University's Winship Cancer Institute in Atlanta, says, "This is the strongest of the studies I've seen so far that aromatase inhibitors are more effective than tamoxifen, and it will sway a lot of people. But the problem is that aromatase inhibitors cause significant osteoporosis, and one worries that you might be buying a woman worse problems down the road."

Another issue, Brawley adds, is the higher cost of aromatase inhibitors compared with tamoxifen. That cost differential might lead some women to stop taking the drugs before the therapy is completed.

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