Any amount of exercise -- even walking an hour a week -- helped promote breast cancer survival. Walking more than three to five hours a week didn't appear to be any more beneficial. 'Women do not have to run marathons for maximum benefits.'

"Women with breast cancer have little to lose and much to gain with exercise," said Dr. Michelle Holmes, a Brigham & Women's Hospital researcher and the study's lead author.

Exercise had the greatest benefit on women whose cancer was most susceptible to hormone levels -- the most common type of breast cancer.

That suggests that exercise may improve the chances of survival by reducing hormone levels and suppressing tumor growth and recurrence, Holmes said.

Susan de Vries, a Swampscott mother of three with breast cancer, hits the gym four to five times a week. Walking on the treadmill is part of her workout.

She said exercise helps her both mentally and physically.

"It makes me feel great. The mind-body connection is very important for people living with breast cancer," said de Vries, 43. "If you are proactive in any way, it helps."

The study included nearly 3,000 women in the Nurses' Health Study who were diagnosed with breast cancer between 1984 and 1998. The women -- all nurses -- were tracked by questionnaires until June 2002.

Although Holmes said walking shouldn't replace the standard treatments for breast cancer, the results suggest those who exercise may live longer.

The research team found that any amount of exercise -- even walking an hour a week -- helped promote breast cancer survival.

Walking more than three to five hours a week didn't appear to be any more beneficial.

"Women do not have to run marathons for maximum benefits," Holmes said.

Other studies have found that physically active women with breast cancer have better moods, body image and self-esteem.

The findings appear in today's Journal of the American Medical Association.