The surprising ways exercise helps the body fight cancer

For decades, doctors have recommended exercise to help cancer patients manage treatment side effects and improve their quality of life. But a landmark new study suggests exercise doesn’t just help cancer patients feel better—it may help keep cancer from returning.

The 2025 CHALLENGE Trial, published in the New England Journal of Medicine, was the first large randomized controlled study to test whether a structured exercise program could improve long-term outcomes for colon cancer patients after they had completed surgery and chemotherapy. After a median follow-up of eight years, patients with stage 2 and 3 colon cancer who participated in the program had a 28 percent lower risk of disease recurrence, a new primary cancer, or death than those who received exercise education alone. They also had a 37 percent lower risk of death from any cause. According to the study authors, the magnitude of the survival benefit was similar to that seen with many approved cancer drug therapies.

The findings mark a turning point for the growing field of exercise oncology. While no one is suggesting exercise should replace standard cancer treatments, mounting evidence suggests it should be integrated into standard cancer care alongside these therapies, says Sharlene Gill, an oncologist at the University of British Columbia and a co-author of the CHALLENGE Trial.

“The conventional pillars of cancer treatment are surgery, radiation, and chemotherapy with everything else being supportive,” says Gill. “Exercise has moved from not supporting that fight but having the ability to change the outcome of that fight.”

The results are “remarkable,” says Melinda L. Irwin, deputy director of the Yale Cancer Center and Susan Dwight Bliss professor of epidemiology and associate dean of research at Yale School of Public Health. Beyond demonstrating a statistically significant benefit, she says, the study found an effect large enough to meaningfully improve patients’ lives.

The shift has created a burgeoning interest in exercise oncology, including the 2024 formation of The International Society of Exercise Oncology and the growing number of facilities worldwide offering structured exercise programs for cancer patients.

Some experts now envision a future in which an exercise prescription becomes as routine as other parts of a cancer treatment plan.

How exercise helps make the body inhospitable to cancer

Researchers are still working to understand exactly how exercise influences cancer outcomes. One reason cancer is so difficult to fight is that cancer cells are notoriously adept at evading detection by the immune system. But evidence increasingly suggests physical activity affects several biological pathways that help create a less hospitable environment for tumors.

“The idea is not that exercise directly ‘cures’ cancer on its own, but that it may help create a physiologic environment that is less favorable for cancer growth and more supportive of the body’s natural anti-tumor defenses,” says Irwin.

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Exercise appears to strengthen the body’s surveillance system by increasing the activity of immune cells—including natural killer cells and T cells—that seek out and destroy abnormal cells. One study hypothesized that exercise might alter tumor microenvironments, making cancer cells less effective at maintaining barriers that prevent immune cells from entering and destroying them.

Exercise may also counter chronic inflammation, another force that helps tumors thrive. Physical activity decreases the activity of cytokines such as IL-6 and TNF-α, which promote inflammation. This lowering of inflammatory signaling might create a biological environment less supportive of tumor progression, explains Irwin.

Exercise may also affect cancers driven by hormonal and metabolic pathways, such as breast cancer, which can be associated with high estrogen levels. Regular aerobic exercise decreases levels of circulating estrogen in pre- and postmenopausal women and helps reduce fat tissue—the primary source of estrogen production in postmenopausal women, explains Gill.

Exercise also helps regulate insulin-like growth factor 1 (IGF-1), a hormone involved in cell growth that has been linked to increased cancer risk when elevated. Physical activity can also improve insulin sensitivity, helping counter a metabolic state associated with higher cancer risk and poorer outcomes.

Researchers hope to better understand those mechanisms in the next phase of the CHALLENGE Trial, which will analyze participants’ blood samples to identify the biological changes associated with exercise.

What researchers still don’t know

Despite the excitement surrounding exercise oncology, researchers caution that many important questions remain unanswered.

One of the biggest is what type of exercise provides the greatest benefit. Most research to date has focused on the benefits of aerobic exercise, with one study concluding that moderate-intensity endurance exercise was the most effective form for preventing cancer metastasis. But only limited research has been done on the benefits of resistance or combined training.

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Researchers are also still trying to determine the optimal dose. Participants in the CHALLENGE Trial completed about 150 minutes of moderate-intensity exercise each week, but scientists do not yet know whether smaller amounts could provide similar benefits, says Irwin.

Then there’s the question of what types and stages of cancer might benefit from exercise. So far, research has focused on localized colon, breast, and prostate cancers.

“Are these results applicable to other cancers? We don’t know yet,” says Gill. “But it’s not unreasonable to extrapolate these findings to other cancers. If patients have more active or advanced disease it becomes more difficult to extrapolate the results that exercise may extend life.”

Exercise oncology is growing—but access remains limited

At Manhattan’s Memorial Sloan Kettering Cancer Center, patients can be referred to a specialized exercise oncology program as soon as they are diagnosed with cancer, says Jessica Scott, the director of the exercise oncology program. There, exercise physiologists develop individualized plans that continue through treatment and recovery, adapting recommendations based on a patient’s fitness level, risk factors, and changing needs.

Programs like this are becoming increasingly common. An estimated 2,100 cancer exercise programs exist in the U.S. at hospitals, university-affiliated facilities, or community settings. Yet access remains one of the field’s biggest challenges.

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The American Society of Clinical Oncology recommends that patients engage in regular aerobic and resistance exercise during treatment. But exercise has not yet been incorporated into standard-of-care guidelines in the United States. (This year, the European Society for Medical Oncology adopted exercise as guideline-therapy for localized colon cancer.) That means insurance typically won’t cover programs, so patients need to rely on institutional funding or pay out of pocket, says Scott.

That shift will likely take years. But Gill argues patients do not need to wait for health systems to catch up. “Everyone can take control of this part of their journey by doing just 150 minutes a week of brisk walking or any activity they enjoy,” she says.

It might not happen tomorrow, but Scott says the goal is to have exercise oncology sessions be as routine for cancer patients as cardiac rehabilitation is for heart patients.

“My dream is every single patient diagnosed with cancer will have access to a program and an individualized exercise prescription,” says Scott.