A drug that inhibits the manufacture of estrogen can lower the likelihood of breast cancer among healthy women whom doctors consider at risk of developing the disease. The drug, called exemestane, may offer a preventive approach to combating the malignancy, the study authors reported June 4 at a cancer meeting in Chicago and online in the
New England Journal of Medicine
Two drugs called tamoxifen and raloxifene have previously been shown to lessen breast cancer risk when taken as preventives. Those drugs hamper the pro-growth effects of the hormone estrogen, which is implicated in most breast cancers. But while tamoxifen is commonly used as a treatment for already-diagnosed breast cancer, few cancer-free women take it as a preventive despite being deemed at risk, the study authors note.
Exemestane, a different kind of cancer-fighting drug called an aromatase inhibitor, lessens the amount of estrogen made in the body by hampering the activity of enzymes called aromatases.
In the new study, the scientists enrolled 4,560 women considered at risk of breast cancer because they were age 60 or older, had abnormal breast-cell growth considered a marker of cancer risk or had an array of other factors such as a close relative with breast cancer. All were postmenopausal, none had any previous invasive breast cancer and none carried a genetic mutation that would predispose them to the disease. Their average age was 62.5 years.
The researchers randomly assigned roughly half to get exemestane and half a placebo pill. After a median follow-up of 35 months, 11 invasive breast cancers had appeared in the exemestane group compared with 32 among the placebo recipients. Invasive breast cancer, also called infiltrating breast cancer, is dangerous because it spreads beyond its point of origin to other areas within the breast and is prone to jumping to nearby lymph nodes or to other organs.
The results suggest that taking an aromatase inhibitor such as exemestane reduces a woman’s risk of developing invasive breast cancer by 65 percent, says study coauthor Paul Goss, a physician at Harvard Medical School in Boston.
While that rate indicates a substantial lessening of risk, the absolute annual incidence of breast cancers in each group was less than 1 percent, the data show. Hot flashes, sweating, fatigue and insomnia were slightly more common among women on exemestane, but women in both groups rated their overall quality of life about the same.
During the study, which ran from 2004 to 2010, nearly 33 percent of the exemestane group had stopped taking their pills, as had almost 29 percent among those assigned placebos.
Nevertheless, the study “was well conceived and cleanly executed,” say Nancy Davidson and Thomas Kensler of the University of Pittsburgh, writing in a New England Journal of Medicine editorial. The findings “support the use of exemestane as an option for risk reduction in postmenopausal women at high risk for breast cancer,” they conclude.
Exemestane is marketed as Aromasin by its maker Pfizer, which funded the study.