Running mice give evidence about skin cancer, colorectal cancer

Two papers published this week in the journal Carcinogenesis talk about the inhibitory effects on cancer of voluntary exercise in mice.

In the first paper, researchers looked at inhibition of skin cancer induced by ultraviolet light (UVB). Using a special mouse line under two different cancer-inducing conditions, they sum up their results with:

…voluntary running wheel exercise delayed the appearance of tumors, decreased the number of tumors per mouse and decreased tumor volume per mouse.

The effects described here indicate that voluntary running wheel exercise inhibits UVB-induced skin tumorigenesis and may also inhibit tumor growth.

The mouse line used is a model for skin cancer in humans: it has a mutation in a gene linked to skin cancer, meaning that these mice are very susceptible to UV-induced skin cancer. The two conditions used were:

• ‘High risk’, meaning the UV dose given was enough to give the mice at a very high chance of getting skin cancer.
• ‘Complete’, which is the same UV dose as the ‘high risk group’, but given for a longer time. This virtually guarantees incidence of cancer in these mice.

The beneficial effects of exercise was found in both groups. How applicable this finding is to humans remains to be seen, though, but it’s a good sign.

The second paper showed that voluntary exercise and a restricted diet reduced the number and size of pre-cancerous polyps in the intestines of male mice and improved survival. The study is the first to suggest that a "negative energy balance" appeared to be the important factor in inhibiting the growth of polyps, which are the forerunners of colorectal tumors. A negative energy balance is produced by increasing the mice’s energy output by use of a running wheel, while maintaining a restricted calorie intake; that is: mice ate less food than they would have needed to offset the increase in exercise.

Lead researcher Lisa Colbert summed it up for us:

"The exercising mice ran an average of 3.8 km a day, and the further they ran the fewer polyps they had. Exercise significantly reduced total polyp number and polyp size, as well as prolonging survival. On average, there were 16 polyps per mouse in the exercising mice compared to 22 polyps in the control mice - a decrease of 25 percent."

Again, studies looking at humans are necessary before making any medical claims, but this is another excellent lead.

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