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* Cuts breast cancer risk 65 pct in high-risk population
* Now available as generic, cost has dropped (Recasts first paragraph, adds physician and company comments)
By Debra Sherman
CHICAGO, June 4 (Reuters) - The estrogen-blocker Aromasin was found to reduce the risk of developing breast cancer by 65 percent in post-menopausal women at high risk for breast cancer, researchers said on Saturday.
A late-stage trial of 4,560 post-menopausal women who were at increased risk of developing breast cancer found that those who took the drug, also known as exemestane, had fewer invasive breast cancers after 3 years and without severe side effects.
"We are delighted with this two-thirds reduction," Dr. Paul Goss, director of Breast Cancer Research at Massachusetts General Hospital, said in an interview.
He noted that there were fewer of the more aggressive types of tumors in patients who took the drug, but the limitation of the study was that the median follow-up was just 3 years.
The drug is sold by Pfizer Inc (PFE.N) under the brand name Aromasin, which lost its patent April 1, 2011 and is now available in a cheaper generic version.
The results of the study were presented in Chicago at the annual meeting of the American Society of Clinical Oncology.
An estimated 1.3 million women are diagnosed with breast cancer worldwide each year and nearly 500,000 die of the disease. It is the second leading cause of cancer death among U.S. women after lung cancer.
The study, which was sponsored by Pfizer, broke participants up into two groups: One got the drug and the other got a placebo. There were 11 invasive breast cancers reported in the drug group compared with 32 in the placebo group. There were also fewer cases of precursor lesions in the group that got exemestane.
Goss, who led the study, noted that tamoxifen has been used for years to prevent breast cancer, but had serious side effects, including raising the risk of developing uterine cancer, cataract formations and stroke.
Exemestane did not cause high levels of toxicity, he said. Its side effects were much milder that those seen with tamoxifen, he said, although there was a slight increase in osteopenia -- low bone density, but not low enough to be classified as osteoporosis.
Other side effects reported in the study included hot flashes, sweating, fatigue, and insomnia.
"Age is the single biggest risk factor for developing breast cancer. Once you are 60, your risk increases so this (research) merits consideration for prevention. What we don't know is whether patients need to take this pill for life."
After 5 years, there was no dangerous accumulation of toxicity from the drug, he said.
"I can't look someone in the eye and swear it won't be (toxic over a longer period of time), but there's large evidence that the drug is safe," Goss said.
People have been taking statins to lower cholesterol and antihypertensive medications to reduce blood pressure for years, Goss noted. "This is the same concept."
And the price of exemestane has fallen significantly.
Commercially, even with its patent still protected, Pfizer's Aromasin was only a moderate seller in first quarter, with sales down 11 pct to $114 million.
The once-a-day oral tablet was originally approved to treat advanced breast cancer in post-menopausal women who had already been treated with tamoxifen for 2 to 3 years. The drug is also used to treat women whose breast cancer worsened while they were taking tamoxifen.
Exemestane belongs to a class of breast cancer drugs known as "aromatase inhibitors," which work by decreasing the amount of estrogen the body produces. Lower estrogen levels can slow or even stop the growth of some breast tumors that need estrogen to grow.
Dr. Andrew Seidman, an oncologist at New York's Memorial Sloan-Kettering Cancer Center, called the results exciting because exemestane gives high-risk women an alternative to tamoxifen and to a double mastectomy just to prevent getting the disease.
Goss said he wondered whether Pfizer would try to extend the patent based upon this new preventative indication.
A Pfizer spokesman declined to comment on the drugmaker's regulatory plans.
"What we can say is that the ongoing evaluation of Aromasin by the research community contributes to a growing body of knowledge in breast cancer and may help clinicians and patients determine the best use of aromatase inhibitor therapy," the spokesman said.
Reporting by Debra Sherman, Editing by Sandra Maler