The National Cancer Institute paid for the study, which was led by Melinda Irwin of the Yale Cancer Center and Dr. Jennifer Ligibel of the Dana-Farber Cancer Institute in Boston.
Dr. Eric Winer, breast cancer chief at Dana-Farber, said the results may help more women stick with the drugs.
“A lot of people will say, ‘if it’s going to have a lot of side effects, I’m not going to do it.’ The truth is, not everyone gets symptoms. Exercise might be a solution,” he said.
The other study was led by Dr. Jack Cuzick of Queen Mary University of London and tested anastrozole for preventing first breast cancers. Nearly 4,000 women were given the drug or daily dummy pills, and 70 percent stuck with them for five years, just a little less than the placebo group.
After that time, 40 women on anastrozole had developed breast cancer versus 85 of the others, a 53 percent reduction in risk. That’s comparable to how another aromatase inhibitor — exemestane, or Aromasin — did in an earlier study and better than tamoxifen, the longest-used breast cancer prevention medicine.
Women on anastrozole had more joint pain and hot flashes, but these also were very common in the placebo group — more than half of both groups reported these problems, which often are due to menopause and aging, Cuzick said. Anastrozole users had more cases of a painful wrist condition called carpal tunnel syndrome, and dry eye, but these were relatively rare. Aromatase inhibitors are known to raise the risk of fractures, so many women take bone-strengthening drugs to help prevent that problem.
Besides the British cancer research agency, London-based AstraZeneca PLC, which makes the anastrozole used in the study, Arimidex, helped pay for the work, and some researchers are paid speakers for the company.