Can Exercise Help us Beat Cancer?

In a study performed at Massachusetts General Hospital in Boston and Memorial Sloan Kettering Cancer Center in New York City, Dr. Mark W. Dewhirst performed an study that tested the hypothesis that exercise improves the flow of nutrients and oxygen to tumor tissues which in turn reduces the tumor’s growth rate. It has already been confirmed that exercise does increase the flow of nutrients and oxygen to normal, healthy tissues. This study was performed on female mice that had been implanted with breast cancer tumors, but still possessed functional immune systems, which improves the ability to make conclusions based upon the data, but inhibits the application of these conclusions on human immune systems.

The female mice were randomly selected to be placed in a group of voluntary wheel exercise, or in a group of forced sedentary lifestyle. There were 11 mice in the exercise group and 12 in the sedentary group. The mice were observed 3 times a week for 18 days, which is a significant period of life in mice. At the end of the 18 days, it was shown that there was a statistically significant decrease in tumor growth rate in the exercise group, compared to the sedentary group. From tumor extracts, the observers were able to observe that there was a 1.4 fold increase of apoptosis in the exercise group of mice, meaning that the tumor cells were targeted and killed by the mice’s immune system. It is believed that this may have been due to an increase in Fas receptors from exercise, which are related to the activation of apoptosis.

As well as a greater amount of apoptosis, the overall improvement of vessel function within the tumor tissues was observed in the exercise group. Between the two groups of mice, microvessel density within the tumor was significantly higher in the exercise group. This would result in a greater distribution of blood within the tumor tissues. Vascular maturity was also 3 to 4 times greater in the exercise group, allowing for an increase in oxygen transport to the tumor tissues. Finally, the exercise group of mice seemed to induce an increase of expression for key regulators that aid in the activation of the growth of new blood vessels around the tumor. Hypoxia is the state of oxygen and nutrient deprivation within cells, and the increase of vessel function within the tumors of the exercise group of mice resulted in the statistically significant lowering of this state in the tumor tissues. However, it is unclear why the reduction of the state of hypoxia alone would increase the rate of cell death within the tumor.

Next the observers decided to test the hypothesis that chemotherapy was more effective when coupled with exercise that reduced the state of hypoxia in the tumor tissues. Four groups of 17 female mice were formed, each inserted with a breast cancer tumor. One group was subjected to voluntary exercise on a wheel, one was sedentary, one was subjected to a cancer drug called cyclophosphamide, and another was subjected to both exercise and cyclophosphamide. In this study, the rate of tumor growth in the mice was measured 3 times weekly until the death of the subject. It was observed that the group of mice subjected to cyclophosphamide and exercise had a tumor growth rate significantly lower than any other. There was no difference in the growth rate of tumors in the exercise group and the cyclophosphamide group, however, both of these groups possessed a significantly lower rate than the sedentary group.

Based upon the results of these two studies, Dr. Dewhirst and his colleagues concluded that aerobic exercise induces angiogenesis, which leads to the reduction of the state of hypoxia in tumor tissues. This means that there is more oxygen available within the tumor’s environment, which allows chemotherapy drugs to act more effectively and slow the growth rate of tumors. These conclusions should be interpreted with caution, however, as humans posses slower-growing tumor models, and so exercise may not be as effective within this model. It should also be noted that in the study, exercise was only coupled with only one chemotherapy drug, and it is unclear if exercise would allow other chemotherapy drugs to be more effective as well. The data observed in the first study should also be highlighted due to a large spread of data points within the exercise group, which when considering the small sample size of mice, results in less conclusive data. The amount of exercise performed by each mouse was not discussed as well, leading to more inconclusive data. Meaning that the lower growth rate of tumors in the exercising mice may not have actually been statistically significant, and thus it is not conclusive that exercise does reduce the rate of growth of tumors.

The work by Dr. Dewhirst and his colleagues is extremely important, however, because it suggests that aerobic exercise could be useful in the therapeutic treatment of cancer in humans, whether coupled with chemotherapy or not. However, more studies must be performed, preferably with a greater sample size and more controlled factors so that more definite conclusions can be made. Ensuing studies should attempt to answer whether exercise is able to aid the effectiveness of a multitude of chemotherapy drugs, can aid in the treatment of multiple types of cancers, and most importantly, can aid in the treatment of a human model of tumors.

Dr. Dewhirst’s work can be connected to the fact that biological systems are affected by disruptions to their dynamic homeostasis, as is seen when tumor tissues are able to grow out of control when a state of hypoxia sets in. The loss of essential oxygen and nutrients damages the homeostasis of those tissues and allows the tumor to grow even more in the chaotic environment. By restoring the environment of the tumor tissues back to order through angiogenesis, the tumor’s growth rate decreases and apoptosis can take place at a greater rate, combatting the tumor cells.

Here is the a link to the article published by Dr. Dewhirst and his colleagues in The Journal of National Cancer Institute: http://jnci.oxfordjournals.org/content/107/5/djv040.full

Here is a link to an article written by Gretchen Reynolds on the New York Times website that discusses the study as well: http://well.blogs.nytimes.com/2015/03/25/how-exercise-may-aid-cancer-treatment/