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Pfizer Drug Prevents Breast Cancer in Healthy, At-Risk Women

Pfizer Inc.’s Aromasin, used to treat breast cancer and stop it from returning, also prevents tumors from developing in healthy women at risk for the disease, with fewer side effects than existing options, a study found.

Women at least 60 years old or with a previous diagnosis of precancerous lesions who took Aromasin for three years were 65 percent less likely to have invasive breast cancer than those given a placebo, research showed. A report on the data, funded by New York-based Pfizer, was presented today at the American Society of Clinical Oncology meeting in Chicago.

Breast cancer strikes 1.3 million women worldwide a year, researchers said. While generic tamoxifen and Evista, made by Indianapolis-based Eli Lilly & Co., are approved for prevention, rare and sometimes deadly side effects such as stroke and blood clots limit their use, said Paul Goss, head of breast cancer research at Massachusetts General Hospital in Boston. There were no serious side effects in the study of 4,560 women, he said.

“This drug is a major step forward in terms of side effects and removes one of the major obstacles to prevention,” Goss said in a telephone interview. “The pool of women who are eligible for this may be even larger than the group we studied because the toxicity profile is so favorable.”

Goss said that while follow-up for the study was short, the researchers were “optimistic that with further data it will be maintained.”

Aromasin generated $483 million in sales last year for Pfizer, the world’s biggest drugmaker. The company lost U.S. patent protection for the treatment in April, and will lose marketing exclusivity in Europe and Japan in July, said Chris Loder, a company spokesman, in a telephone interview.

‘Mixed Blessing’

The result is that Pfizer isn’t expected to file for U.S. Food and Drug Administration approval of the drug for breast cancer prevention, Goss said.

“It’s a mixed blessing not having regulatory approval pending,” Goss said. “It would imply a drug company would be pushing it, and the cost would be beyond the reach of many women. The price has already come down dramatically.”

Doctors can prescribe approved drugs for any indication.

Aromasin, along with AstraZeneca Plc’s Arimidex and Novartis AG’s Femara, work by blocking the production of the hormone estrogen that can fuel cancer growth. This was the first study to examine the use of the drugs, called aromatase inhibitors, for preventing cancer.

Tamoxifen prevents tumor cells from using estrogen. Two-thirds of all breast cancers rely on estrogen to grow, according to the National Institutes of Health.

Invasive Breast Cancer

Invasive breast cancer was diagnosed in 11 women taking Aromasin, compared with 31 of those given placebo. There were no differences in fracture rates, cardiovascular complications or other cancers, according to the study that was simultaneously published by the New England Journal of Medicine.

The findings should lead to more breast cancer prevention efforts, wrote Nancy Davidson and Thomas Kensler, from the University of Pittsburgh Cancer Institute, in an editorial that accompanied the study in the New England Journal of Medicine.

“Breast cancer is the second most common cause of death from cancer and one of the most feared diagnoses for women in the United States,” they wrote. “We have the knowledge and tools to reduce its incidence today. We have run out of excuses. What are we waiting for?”

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