Cancer patients are often advised to exercise, and it’s easy to understand why. A cancer diagnosis is life-shattering, so patients often fall into a deep depression, which makes recovery all the more difficult. Far better to challenge oneself with exercise goals, be they hitting a set minutes-per-week target or finishing a half marathon. Exercise can’t guarantee anyone a recovery from cancer, but the opposite—depressed, inactive acceptance of one’s condition—is almost certain to create a downward spiral.

This is the mostly psychological side of exercise and cancer. But are there also physical pathways by which exercise can improve cancer outcomes?Research published in the Journal of the National Cancer Institute indicates that the answer is yes.

Kansas State University exercise physiologist Brad Behnke has been studying prostate-cancer tumor growth in rats that either exercise or are sedentary. As with humans, rats divert blood flow to the muscles when exercising. The result, in Behnke’s research to date, is a 200 percent increase in tumor blood flow during exercise.

That sounds like it could be a bad thing, at least if more blood flow “fed” tumor growth, and accelerated metastasis (spread of the disease to other organs). However, the opposite is what occurs, according to Behnke.

“When a tumor lacks oxygen, it releases just about every growth factor you can think of, which often results in metastasis,” he explained to Runner’s World Newswire by email. “Simply speaking, the tumor says, ‘I can’t breathe here, so let’s pick up and move somewhere else in the body.’”

When a tumor is bathed in oxygen, on the other hand, its activity tends to slow.In an earlier paper, Behnke demonstrated a 90 percent decrease in “tumor hypoxia” (low oxygen) among rats that engaged in long-term, moderate-intensity treadmill exercise. “As far as I know, this is the largest reduction in tumor hypoxia of any intervention, including drugs,” he said.

Another study by a different group of researchers has shown that aerobic exercise can lead to “normalization of the tissue microenvironment in human breast tumors.” In other words, exercise can help the tissue return to its pre-tumor state, or forestall development of a more aggressive and dangerous cancer.

In addition, greater blood flow and oxygen delivery to a tumor can potentially increase transport of cancer-fighting therapies to the tumor. For example, exercisers respond better to radiation treatments, Behnke said. Exercise increases blood flow by increasing blood pumping and pressure, and by decreasing blood vessel constriction.

Behnke’s research has focused on low- to moderate-intensity exercise such as brisk walking or slow jogging, and human studies have not been conducted yet.

“There really aren’t any negative effects to moderate-intensity exercise,” he said. “Exercise improves the side effects of cancer and treatments, but what the exercise does to the tumor is likely beneficial as well.”