AstraZeneca’s Arimidex Halves Breast Cancer Risk, Study Finds

AstraZeneca Plc’s cancer drug Arimidex more than halved the chance of at-risk women developing tumors when used preventively, according to a study published in The Lancet medical journal today.

In a trial among almost 4,000 post-menopausal women at high risk of the disease, those who took Arimidex for five years were 53 percent less likely to develop breast cancer than those who received a placebo, researchers led by Jack Cuzick at Queen Mary University of London’s Centre for Cancer Prevention wrote in the article.

The findings confirm those of a 2011 trial involving Pfizer Inc.’s Aromasin and show that Arimidex, also known as anastrozole, should be preferred to an older and more toxic drug, tamoxifen, by regulators for women who are predisposed to developing breast cancer, Cuzick and colleagues said in a statement.

“We now know anastrozole should be the drug of choice when it comes to reducing the risk of breast cancer in postmenopausal women with a family history or other risk factors for the disease,” Cuzick said.

Breast cancer is the most common form of cancer in women and over 508,000 died in 2011 due to the disease according to the World Health Organization.

Arimidex, which lost patent protection in 2010, earned London-based Astra $543 million in sales last year, revenue that is estimated to fall to $353 million this year, according to the average of 11 analysts surveyed by Bloomberg. The drug and Pfizer’s Aromasin belong to a class of medicines called aromatase inhibitors, which suppress levels of estrogen that can fuel cancer growth.

Joint Pain

Among the 1,920 women who took a daily dose of Arimidex for five years, there were 40 cases of breast cancer, compared with 85 cases among the 1,944 women who got a placebo, the researchers found. Those receiving the drug had more joint pain.

Still, the study found no difference in the likelihood of death between the two groups, suggesting breast-cancer mortality gains with the therapy could be small and that side effects outweigh its benefits, David Cameron, chairman of oncology at the Edinburgh Cancer Research Centre, wrote in an editorial accompanying the study.

“For any woman considering five years’ anti-estrogen therapy to reduce her risk of breast cancer without evidence to suggest that she will have a longer life, the perceived and actual toxicity of this intervention becomes important,” Cameron wrote. “The financial costs of breast cancer chemoprevention might have decreased, but the toxicity cost to women has not.”

The trial found a bigger reduction in more dangerous tumors, suggesting that a life-extending benefit will “very likely” be seen with time, Cuzick said in an e-mailed response to questions.

Funding for the study was provided by Cancer Research U.K., the National Health and Medical Research Council Australia, Sanofi and AstraZeneca.

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