The large, well-respected study of U.S. nurses, has found that breast cancer patients who walk or do other kinds of moderate exercise for three to five hours a week are about 50 percent less likely to die from the disease than sedentary women and adds credible support to sound evidence that healthy lifestyle factors such as eating well and exercising regularly provide significant health benefits.

The protection offered against cancer recurrences appears to be on a par with chemotherapy and even the newer hormonal and drug treatments.

Although physical activity is no substitute for medical treatment, and very often difficult for exhausted cancer patients, the researchers who conducted the study, and other experts in the field say the findings indicate breast cancer patients should try to exercise regularly after undergoing standard care to maximize their chances of surviving.

Michelle D. Holmes of the A new study is the first to produce evidence that exercise improves the prospects of beating a malignancy, and proves that being physically active boosts the odds that breast cancer patients will survive the disease.

The women were monitored through 2002 and the researchers found that any amount of exercise, even walking one hour a week, increased the odds of surviving. The degree of protection increased with the amount of activity up to about three to five hours a week.

Of the 959 women who got the least exercise, which was less than three hours a week, 110 died of breast cancer. In comparison, of the 335 women who got three to five hours of exercise a week, only 20 died of the disease.

The findings held up even after other factors which could confuse the analysis, such as smoking and eating habits were accounted for.

The benefit was greatest for women whose breast cancer was sensitive to the hormone estrogen, which is the most common form. Previous research had shown that exercise lowers the levels of estrogen, which can fuel the growth of breast cancer cells.

The results indicate that breast cancer patients who follow current government guidelines for physical activity could significantly boost their chances of surviving.

Saslow, speaking for the cancer society does caution that the findings should not be misinterpreted to mean that just because someone exercises they are guaranteed to survive, or that they should feel guilty or be blamed if they do not exercise.

As Anne McTiernan of the Fred Hutchinson Cancer Research Center in Seattle says many patients end up exercising less because they are worn out by the treatment.She says that women should try to avoid that and really try to exercise after their treatment, if possible, a few hours of brisk walking will do.

The study is published in the current issue of the Journal of the American Medical Association.