To improve the quality of life of people with cancer, oncologists have regularly recommended exercise. Staying fit can make patients feel and function better. But exercise itself was never considered a formal treatment for the disease.
“The thinking in the medical community was that you need biomedical interventions—surgery, radiation therapy, drugs—to treat cancer,” says Kerry Courneya, a professor of kinesiology at the University of Alberta who studies physical activity and cancer.
That thinking is changing. This year strong evidence emerged that exercise lengthens survival times and lowers recurrence risk for several cancer types. Such benefits are usually ascribed to medicine or surgery. But “exercise treats cancer as well as, if not better than, some of the current drugs that we’re offering our patients,” says Courneya, who led the first large randomized, controlled trial of the effects of workouts on cancer outcomes. It was published in July in the New England Journal of Medicine and involved more than 800 colon cancer patients. Participants with stage 3 and high-risk stage 2 cancer were assigned to a structured exercise program in addition to their oncology care. In a 10-year follow-up period, these people had a 28 percent lower risk of cancer recurrence, new cancers or death than similar patients who received only educational material about physical activity.
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These results prompted a standing ovation when presented to the American Society of Clinical Oncology at a meeting in June. They’re not the only good news in the field. For 10 different kinds of cancer—breast, prostate, colon, lung, oral, endometrial, respiratory, rectal, bladder and kidney—a 2025 longitudinal study of more than 90,000 cancer survivors in the U.S. found that people survived longer if they engaged in moderate to vigorous physical activity after their diagnosis. Even small amounts of exercise made a difference, but 150 to 300 minutes a week of moderate-intensity activity, such as brisk walking, was the most effective intervention.
There was a modest additional benefit with higher levels of activity. (Overall, the effect size varied for different cancer types.) Randomized trials of exercise interventions are now underway for breast, ovarian, esophageal and lung cancer, among others.
There had been early hints that exercise provided this kind of help. For instance, a 2011 study showed that men with prostate cancer who did three or more hours of vigorous exercise a week had a reduced risk of death from the disease. Other studies had similar results for breast and colon cancer.
Strong evidence emerged that exercise lengthens survival times and lowers recurrence risk for several cancer types.
What is it that exercise is doing inside the body that has this therapeutic effect? Exercise triggers so many biological changes at once that it’s hard to say for sure. But there are several possibilities, and it’s likely they work in combination.
A reduction in overall inflammation is probably a factor, says epidemiologist Stacey Kenfield of the University of California, San Francisco. Another important benefit of exercise is that it makes it easier for the hormone insulin to bind to cells, which brings them fresh energy. When insulin isn’t able to bind, the body starts to make more. That’s bad because cancer cells may use insulin to grow and divide more quickly.
Myokines, which are proteins released by muscle tissue, could also be important. In the laboratory, serum with high amounts of myokines reduced the growth of prostate cancer cell lines. In studies of men with prostate cancer published in 2022, Kenfield and her colleagues found that levels of myokines were higher right after a half hour of training with vigorous exercise—and in men who had been exercising for six months—compared with levels in a group of cancer patients who weren’t training.
Workouts also seem to mobilize parts of the immune system that keep cancer in check, says immunologist Per thor Straten of the Center for Cancer Immune Therapy in Denmark. In mice, he has shown that voluntary exercise leads to an influx of immune cells into tumors, as well as a more than 60 percent reduction in tumor incidence and growth. During exercise, Straten says, immune system components called natural killer cells and T cells increase significantly in number. “They’re really effective killers against cancer cells,” he says.
Straten and his colleagues are working on an ongoing randomized trial for lung cancer patients, and they hope it will show that this immune response occurs in people. Supporting findings have appeared in early data from a 2025 study in the U.K. In a small randomized trial of patients with esophageal cancer, half of the participants engaged in structured exercise while undergoing chemotherapy, and half were in a group without a structured program. The tumors of patients who were exercising appear to contain more T cells and natural killer cells.
Experts say the regularity and intensity of exercise matter. “You need to get the heartbeat up” to stimulate the immune system, Straten says. In the colon cancer study, participants chose their type of exercise but received support such as supervised workout sessions and guidance on behavioral change. That helped them stick with the program, Courneya says. “You can’t just advise people to do more exercise and expect them to do it,” he explains.
Now many cancer centers are assessing how to provide that kind of support in addition to their medical offerings. If they don’t, experts say, the centers won’t be delivering on a new standard of care.
This article was made possible by the support of Yakult and produced independently by Scientific American’s board of editors.