NEW YORK (Reuters Health) - Several studies suggest exercise may give an immune system boost to cancer survivors, but more research is needed to see if this translates into a lower risk of cancer recurrence, according to Canadian researchers.

Of the six studies they reviewed, four showed that patients who followed a supervised exercise plan during or after cancer treatment had certain improvements in immune system function.

However, the researchers reported in a recent issue of Cancer, problems with the studies' designs make it difficult to draw conclusions from the findings.

"Additional research is needed to determine if physical exercise in cancer survivors may reduce the risk of cancer recurrence and secondary malignancies and increase survival times," according to Adrian S. Fairey and colleagues of the University of Alberta in Edmonton.

But even though the impact of exercise on cancer patients' immune systems is unclear, there is evidence that supervised activity can lessen some of the physical, psychological and emotional symptoms related to cancer and its treatment, Fairey told Reuters Health.

But, the investigator noted, "the majority of physicians are probably unaware of the benefits of exercise in cancer survivors. This is likely due to the fact that researchers have only recently begun to examine the utility of exercise."

The studies Fairey's team looked at were conducted between 1994 and 2000 and followed the effects of several weeks to several months of supervised exercise--which included activities such as riding a stationary bike, walking and resistance-training to build muscle strength.

The researchers found that in four studies, exercising patients showed some improvement in immune system function, including greater activity or better function in certain important immune cells. In addition, some exercisers showed better endurance, less decline in physical performance and greater muscle strength than patients who did not exercise.

Still, the authors pointed out, the problems with these studies, such as their small size or short duration, limit the weight that can be given to the results.

But, Fairey said, "there are larger and better-controlled trials of exercise and immune system function under way."

SOURCE: Cancer 2002;94:539-551.

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