SAN ANTONIO - Exercise might help women beat breast cancer. Researchers found it can ease the achy joints and muscle pain that lead many patients to quit taking medicines that treat the disease and lower the risk of a recurrence.

The study is the first major test of an exercise program for women on aromatase inhibitors. These estrogen-blocking pills, sold as Femara, Aromasin, and other brands, are recommended for five years after initial breast cancer treatment for hormone-driven tumors, the most common type.

The pills also increasingly are being used to help prevent breast cancer in women at high risk because of family history, bad genes, or other reasons.

A separate study found that one of these medicines - anastrozole, sold as Arimidex and in generic form - cut this risk by 53 percent. It's the second aromatase inhibitor shown to lower risk that much.

Despite how effective the drugs are, many women shun them because they can cause aches and pains, hot flashes, and other side effects. About 15 percent of U.S. women have enough risk to merit considering the pills to prevent breast cancer, yet less than 5 percent take them, said Powel Brown, a doctor who is a prevention expert at the University of Texas MD Anderson Cancer Center.

The exercise study involved 121 postmenopausal women taking various aromatase inhibitors to treat breast cancer who complained of achy joints on a pain survey.

About half were assigned to two supervised strength-training sessions a week plus at least 150 minutes of aerobic exercise per week. The rest got advice on the benefits of exercise and did their usual activities.

After a year, joint pain scores fell 20 percent among exercisers and 3 percent among the others. The severity of pain and how much it interfered with daily live also declined more in exercisers.

The exercise group improved cardiorespiratory fitness and lost weight - nearly 8 pounds versus a slight gain in the others. Eighty percent stuck with the program, helped by free access to a gym and a personal trainer.

The other study was led by 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.