A new study has reported that exercise reduces tumor progression in a mouse model of breast cancer and that this is associated with a reduction in inflammation. Numerous population studies suggest an association between exercise and risk of breast cancer. However, the mechanisms involved have not been established, weakening the basis for inferring a causal relationship. In particular, inflammation plays a role in breast cancer progression and exercise has been reported to lower inflammation. However, the anti-inflammatory effects of exercise in breast cancer have not been established.

In the study, female C3(1)SV40Tag mice were assigned either to an exercise or a sedentary group (12 to 14 mice per group). C3(1)SV40Tag mice have been bred to develop mammary tumors by age 16 weeks without being administered a carcinogen or estrogen. Beginning at four weeks of age, the mice in the exercise group were exercised on a treadmill for 60 minutes per day, six days per week for 20 weeks. All of the mice were examined each week for palpable tumors, and their tumor numbers and volumes were noted. The mice were sacrificed at 24 weeks, at which point a more direct measure of tumor number and volume was taken, and mouse plasma was analyzed for inflammation markers (MCP-1 and IL-6).

The number of mammary tumors in mice assigned to the exercise group was approximately 70% of the number in the sedentary group at 24 weeks. Tumor volume was also lower in exercised mice. The reduction in tumor progression observed in mice in the exercise group was associated with reductions in circulating MCP-1 and IL-6, both markers of systemic inflammation. The authors conclude that exercise training had a beneficial effect on tumor progression that may be partly a result of its anti-inflammatory effects.