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Researchers at Dana-Farber/Brigham and Women’s Cancer Center are investigating the link between exercise and lower risk of cancer, including risk of cancer recurrence.

This much is known: A sedentary lifestyle raises the risk of cancer, while physical activity – even moderate exercise – can reduce the risk not only of developing cancer but having a recurrence following treatment. What’s not so clear is exactly why.

“It’s still a little unknown,” says Dr. Jeffrey Meyerhardt, co-director of the Colon and Rectal Cancer Center at Dana-Farber/Brigham and Women’s Cancer Center, who has studied the relationship of exercise and colorectal cancer risk. In a previous study, he and Charles Fuchs, MD, MPH, director of the Gastrointestinal Cancer Center, reported that in patients with stage III colorectal cancer, more physical activity was associated with a lower risk of cancer recurrence and mortality.

According to Dr. Meyerhardt and other researchers, one way exercise can influence cancer risk is by lowering the amounts of insulin and insulin-like growth factors in the bloodstream. These hormones stimulate tumor cells to spread and survive despite the body’s attempts to kill abnormal cells. Studies show physical activity can directly reduce insulin levels, and research on this link is continuing. Jennifer Ligibel, MD, a Dana-Farber/Brigham and Women’s Cancer Center oncologist and director of the Leonard P. Zakim Center for Integrative Therapies, led a study in breast cancer patients that showed that participation in an exercise program led to a reduction in insulin levels in previously inactive breast cancer survivors.

Metformin, a diabetes drug being studied in cancer, also has an insulin-lowering effect. Dr. Meyerhardt and Dr. Ligibel are leading a study in which patients with breast or colon cancer were assigned to an exercise intervention or metformin, or both, or neither for three months. The researchers will analyze blood samples to look for changes in insulin and other factors related to cancer risk.

Exercise can also reduce inflammation, an acute or chronic immune response that can contribute to cancer risk. However, scientists are just beginning to probe the complex connections among exercise, the immune system, and cancer. Dr. Ligibel has led several studies looking at the connection between exercise and cancer risk. She is currently lead investigator for a clinical trial investigating the impact of weight loss on breast cancer recurrence. Researchers are pursuing many leads toward understanding the big picture of exercise and cancer, which undoubtedly will prove to be complicated. For example, Dr. Meyerhardt’s previous studies found that physical activity wasn’t a protective factor in patients with colorectal cancer whose cells lacked a functioning tumor-suppressor gene, P27.

“We know that despite having a certain type of cancer, exercise is not going to be helpful against everyone’s tumor,” he notes. “We’re still a ways from being able to say which patients will benefit most.”

This post originally appeared on Insight, the blog of Dana-Farber Cancer Institute.

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