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It is well accepted that exercise is beneficial for human health and boosts overall energy level. However, the questions remains: can exercise be used as a cancer therapy? Research is indicating that it can. Over the past 20 years, studies have demonstrated that exercise decreases the risk of recurrence in cancer survivors. Even in the short term, exercise benefits cancer patients. A recent study found that breast cancer survivors who did 150 minutes of aerobic exercise and 2 strength-training sessions each week for 12 months had an increased overall quality of life compared to those who did not. How exercise decreases cancer recurrence and increases quality of life, however, is not well understood.
Exercise reduces obesity, insulin, and blood glucose levels, all of which could partially contribute to the increase quality of life. In addition to the above effects, the immune system is also altered after exercise. Although there is no evidence in humans that total immune cell numbers are changed after chronic exercise, there is data that indicates the activity of a certain type of white blood cell, called a natural killer (NK) cell, is increased. NK cells are one type of immune cell responsible for direct tumor cell killing. The tumor killing ability of NK cells is increased after exercise.
Researchers have used mouse models to further understand how exercise effects NK cell function during cancer. Pedersen et al. found that if mice are allowed to voluntarily run for 4 weeks before tumor inoculation, they had significantly smaller tumor growth compared to mice that did not run. This effect was seen in five different mouse tumor models, including a spontaneous model. Exercise after cancer development also resulted in delayed tumor growth in the slow growing tumor models, which grow more like human cancer. The researchers then checked to see what genes were being changed after the 4 weeks of exercise. They found that 52% of genes changed were related to the immune system.
Further investigation showed that exercising resulted in an increased number of NK cells both overall and in the tumor specifically. To test if the presence of NK cells were contributing to the anti-tumor effect, researchers depleted them from the mice. The mice without NK cells no longer responded to the exercise treatment. Thus, the researchers determined that the anti-cancer effect was dependent on NK cells. Finally, the researchers explored how exercise was affecting the NK cells. They found that adrenaline, a chemical produced during exercise, causes the NK cells to migrate to the cancer and kill the tumor cells. This is dependent on the pro-immune molecule IL-6. This communication between the exercise response and NK cells ultimately results in a strong anti-tumor immune response.
If this research applies to humans, the implications are vast. Currently, the top of the line immunotherapies, such as checkpoint inhibitors, only work in a small number of patients. Scientist are currently working on ways to activate the immune system and increase the effectiveness of immunotherapy. Exercise is an easy way to improve cancer therapy with very few side effects. If patients can improve their treatments by simply running on a treadmill, this could revolutionize the field.
Pedersen, L., Idorn, M., Olofsson, G. H., Lauenborg, B., Nookaew, I., Hansen, R. H., … Hojman, P. (2016). Voluntary Running Suppresses Tumor Growth through Epinephrine- and IL-6-Dependent NK Cell Mobilization and Redistribution. Cell Metabolism, 23(3), 554–562. https://doi.org/10.1016/J.CMET.2016.01.011
Kruijsen-Jaarsma, M., Révész, D., Bierings, M. B., Buffart, L. M., & Takken, T. (2013). Effects of exercise on immune function in patients with cancer: a systematic review. Exercise Immunology Review, 19, 120–43. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/23977724I