Aromatase inhibitors and bisphosphonates: Good for breast cancer prevention and treatment

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The past week brought promising news for both prevention and treatment of breast cancer. In the first instance, Dr. Paul E. Goss, professor of medicine at Harvard Medical School and Massachusetts General Hospital, published in the New England Journal of Medicine the results of a randomized study demonstrating that a class of compounds called aromatase inhibitors, specifically exemestane (brand name Aromasin), can prevent breast cancer. Two other drugs, tamoxifen and raloxifene, have already been approved to prevent breast cancer, but have serious side effects. Exemestane works by halting the production of estrogen, and thus tumor growth.

In a randomized, double-blind trial of over 4,500 post-menopausal women in the United States, Canada, France, and Spain, who were identified as being at a higher than normal risk for developing breast cancer, a three-year follow-up found that 11 women who received exemestane had developed invasive breast cancer — compared with 32 women who had been given a placebo. This turns out to be a significant risk reduction of 65 percent.

Despite these positive trial results, it’s difficult to say whether exemestane will see any kind of broad usage in the coming years since aromatase inhibitors are now prescribed only by oncologists; to be used for preventive purposes, they would need to be prescribed by gynecologists and general practitioners, who may not be comfortable with such drugs. And further complicating matters, patent protection on Aromasin expired in April, which means that its maker, Pfizer, has little incentive to seek regulatory approval for the drug’s use in breast cancer prevention. ACSH’s Dr. Gilbert Ross notes that, while the study is a piece of good news, these impediments mean that it will have “little effect on the toll of breast cancer in the real world — that is, in the clinics.”

As for the latest developments in the treatment of breast cancer, researchers from the Medical University of Vienna found that women with early-stage hormone receptor-sensitive breast cancer responded positively to a class of bisphospohonate called zoledronic acid when used alongside standard hormone therapy (tamoxifen or anastrozole). The results of the landmark Austrian Breast and Colorectal Cancer Study Group trial-12 (ABCSG-12), which consisted of 1,800 women enrolled between 1999 and 2006, were published in The Lancet Oncology. Lead investigator Michael Gnant and colleagues found that 62 months following surgery, treatment with zoledronic acid reduced the risk of disease recurrence by 32 percent compared to hormone therapy alone. Noteworthy in this study is that the major beneficiaries were premenopausal women over 40 years of age.