Prevention Study Focuses on Anti-Hormone Therapy

Researchers have long speculated that aromatase inhibitors (AIs), a class of drugs used to treat estrogen-driven breast cancer, could also prevent development of hormone-fueled breast cancers in older women. New research presented at the 2013 annual San Antonio Breast Cancer Symposium involving the AI anastrozole confirms that suspicion.

Results of the IBIS-II Prevention trial show that after a median follow-up of five years, postmenopausal women at high risk of breast cancer who take anastrozole could reduce their risk of developing the disease in half (53 percent), which translates to 2 percent of women developing breast cancer on anastrozole over five years compared with 4 percent of women on placebo.

Jack Cuzick, who serves as director of the Wolfson Institute of Preventive Medicine at Queen Mary University of London, also noted that the researchers were surprised to find that women taking anastrozole also experienced a reduction in developing other malignancies, such as skin, gastrointestinal and gynecologic cancers. He further noted that participants experienced a modest increase in musculoskeletal events. There was a slight increase in fractures, but that such side effects could be controlled with a class of drugs called bisphosphonates used to treat osteoporosis.

AIs work by blocking the enzyme aromatase from converting the hormone androgen into estrogen, but they can sometimes cause debilitating side effects, such as joint pain, bone loss and heart problems. But many of these symptoms are common in postmenopausal women because of the natural decrease in estrogen, Cuzick noted, and are often inappropriately attributed to AI therapy.

"There's a perception that these drugs have high toxicity," Cuzick said at a press briefing prior to his presentation, adding most side effects can be managed and tolerated. "We need to educate people that there are effective ways to reduce breast cancer by up to 50 percent."

However, other experts have argued that the small total difference in the rate of cancers has never been shown to result in fewer breast cancer deaths, which they say must be factored in balancing the benefits against the side effects.