Patients undergoing cancer treatment are often advised by their doctors to continue exercising — if possible — as part of their daily routine. Exercise can improve mood and release stress, two factors that can help cancer sufferers get through treatment. But a new study shows that exercise may also play a role in helping to slow the growth of cancerous tumors and aid in cancer treatment.

The research, published in the Journal of the National Cancer Institute, found that exercise can make it harder for breast cancer tumors to develop, and it can increase the tumors susceptibility to chemotherapy. For the study, which was conducted on mice, researchers inserted breast cancer cells into the tissue of female mice. The mice were then divided into two groups, those that remained sedentary and those that were allowed to run on a hamster wheel at will.

In both groups, the cancerous cells began to form into tumors, but blood testing showed that the tumors grew more slowly in the mice that were active than in those that were not. Researchers found that exercise increased the flow of oxygen to the tumors just as it does to healthy cells within the body. But what was surprising was that this caused the tumors to grow more slowly than the more oxygen deprived — or hypoxic — environment of the sedentary mice.

Next, researchers looked at the effect this oxygen-rich environment had on the chemotherapy medications administered to treat breast cancer tumors. In this study, researchers tested a group of female mice that had breast cancer. Half of the group received chemotherapy drugs while the other half did not. Within each subgroup, one half of the animals exercised, while the other half remained sedentary.

Not surprisingly, researchers found the largest tumors in the sedentary mice that did not receive the chemotherapy medication. Interestingly, the mice that received either chemotherapy treatment or exercise showed similar levels of tumor growth, suggesting that either method could work to inhibit the growth of tumors. However, the mice that both ran and were given chemotherapy drugs saw the slowest tumor growth. Researchers think it's possible that exercise made the tumors more susceptible to the chemotherapy drugs. 

Of course, this study was small and it involved mice, not humans. But even the study's authors were surprised by the effectiveness of exercise in boosting cancer treatment:

“We set about to see whether exercise would affect the tumor perfusion, and could not have guessed that it would be as effective as it was,” said Mark Dewhirst, the Gustavo S. Montana Professor of Radiation Oncology at Duke University School of Medicine and senior author of the study.

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