Giving cancer its walking papers

Content provided by the Faculty of the Harvard Medical School

Giving cancer its walking papers

Research demonstrates that exercise benefits cancer patients.

The health benefits of exercise need little introduction. Besides combating obesity — probably the major health woe for Americans these days — physical activity lessens your chances of developing type 2 diabetes and heart disease and of having a stroke. And if you do get sick, it can be an important part of bouncing back. After a heart attack, regular exercise has been shown to reduce the chances of having another one. Physical activity can help keep the "black dog" of depression at bay.

Breast and colon cancer

A growing body of evidence suggests exercise could benefit cancer patients. In 2005, Harvard researchers found that simply walking on a regular basis helped breast cancer patients. The study focused on about 3,000 women diagnosed with breast cancer who are part of the Nurses' Health Study. Those who regularly walked three to five hours a week (or got comparable exercise) were 50% less likely to have a recurrence of their cancer than women who exercised less than an hour per week.

In September 2006, University of North Carolina researchers reported results showing that obese and overweight breast cancer patients tended to live longer if they had been physically active prior to their diagnosis.

Two other Harvard studies showed exercise benefits for colon cancer patients. One, which also used Nurses' Health Study data, reported that women who had been diagnosed and treated for colorectal cancer and who engaged in the equivalent of six hours or more of walking per week reduced their risk of dying from the cancer by 60%. The other found that colorectal cancer recurrence was half as likely in patients who were physically active for six or more hours per week, compared with those active less than an hour a week.

Why exercise has beneficial effects isn't completely understood, but researchers have some theories. In the case of colorectal cancer, it may help lower levels of insulin and insulin-like growth factor (IGF), which are associated with tumor growth. For breast cancer, a similar mechanism might be at work. In 2005, University of Pennsylvania researchers reported that breast cancer patients enrolled in a yearlong exercise program had significantly lower levels of one type of IGF compared with patients who weren't exercising. Exercise may also have therapeutic benefits for breast cancer patients because it lowers estrogen levels. Estrogen can promote the growth of cancer cells.

One unexplained aspect of these findings: Colorectal cancer patients seem to need twice as much exercise as breast cancer survivors for more or less comparable benefits. The difference especially stands out in the case of the two studies drawing on Nurses' Health Study data, which used the same survey forms to measure physical activity and a similar kind of analysis.

Don't jump to conclusions

Evidence that regular exercise seems to help with breast and colorectal cancer doesn't mean that it will help with other types of cancer. Breast and colorectal cancer are often caught early because of screening tests. Others, such as lung, ovarian, and pancreatic cancer, are usually discovered at a much later stage, when it's much harder to turn things around. In addition, different types of cancers vary in how they get started and grow. Regular exercise may be just the thing to intercept some cancers but not others.

Moreover, the results for breast and colon cancer are actually pretty mixed. A 2002 clinical trial published in Cancer Causes & Control concluded that physical activity didn't influence recurrence of the polyps that lead to colon cancer, which raises the question of how it can cut down recurrence of colon cancer. In 2006, National Cancer Institute researchers reported finding no link between physical activity and a lower incidence of colon cancer. And the University of North Carolina breast cancer study didn't find a survival benefit from exercise for women whose weight was in the normal or underweight ranges.

Dr. Robert Mayer, a co-author of one of the Harvard papers on colon cancer, cautions that people who are more physically active may have less of a cancer burden. In other words, it may not be exercise that explains the positive results but that cancer patients who are able to exercise more perhaps aren't as sick to begin with.

Other benefits

Even if exercise doesn't directly combat cancer, it may help cancer patients in other ways. Survivors of some types of cancers have higher rates of heart disease and osteoporosis; regular exercise can cut those risks. Moderate amounts of physical activity seem to help reduce the fatigue from chemotherapy and radiation, perhaps by countering depression. Emotional benefits shouldn't be discounted.

More research: Researchers always see a need for it. But an editorial in the August 2006 issue of the Journal of Clinical Oncology noted the problem with exercise studies: "There is no doubt that the pharmaceutical industry would back an agent with potential to reduce cancer recurrence by at least 50%, but who will back a trial that evaluates the potential benefit of sneakers and sweatpants?" asked the author, Wendy Demark-Wahnefried. Most likely, the Duke University researcher concluded, it'll be up to the government to undertake the requisite clinical trials, but in any case, "It's time to get moving!"

Last updated:	September 05, 2008