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.
Exercise physiologist Brad Behnke has been studying prostate-cancer tumour 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 tumour blood flow during exercise.
That sounds like it could be a bad thing, at least if more blood flow “fed” tumour growth, and accelerated metastasis (spread of the disease to other organs). However, the opposite is what occurs, according to Behnke.
“When a tumour lacks oxygen, it releases just about every growth factor you can think of, which often results in metastasis,” he explained to Runner’s World. “Simply speaking, the tumour says, ‘I can’t breathe here, so let’s pick up and move somewhere else in the body.’”
When a tumour is bathed in oxygen, on the other hand, its activity tends to slow. In an earlier paper, Behnke demonstrated a 90 percent decrease in “tumour 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 tumour hypoxia of any intervention, including drugs,” he said.
Another study by a different group of researchers has shown that aerobic exercise can lead to “normalisation of the tissue microenvironment in human breast tumours.” In other words, exercise can help the tissue return to its pre-tumour state, or forestall development of a more aggressive and dangerous cancer.
In addition, greater blood flow and oxygen delivery to a tumour can potentially increase transport of cancer-fighting therapies to the tumour. 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 tumour is likely beneficial as well.”
