Abstract
Epidemiological research suggests that regular physical activity confers beneficial effects that mediate an anti-tumor response and may reduce cancer recurrence. It is unclear what amount of physical activity is necessary to exert such a protective effect and what mechanisms are involved. We investigated the effects of voluntary wheel running on tumor progression and cytokine gene expression in the transgenic polyoma middle T oncoprotein (PyMT) mouse model of invasive breast cancer. Runners showed significantly reduced tumor sizes compared with non-runners after 3 weeks of running (p≤0.01), and the greater the running distance the smaller the tumor size (Pearson's r = −0.61, p≤0.04, R2 = 0.38). Mice running greater than 150 km per week had a significantly attenuated tumor size compared with non-runners (p≤0.05). Adipose tissue mass was inversely correlated with tumor size in runners (Pearson's r = −0.77, p = 0.014) but not non-runners. Gene expression of CCL22, a cytokine associated with recruitment of immunosuppressive T regulatory cells, was decreased in tumors of runners compared to non-runners (p≤0.005). No differences in tumor burden or metastatic burden were observed between runners and non-runners after ten weeks of running when the study was completed. We conclude that voluntary wheel running in PyMT mice correlates with an attenuation in tumor progression early during the course of invasive breast cancer. This effect is absent in the later stages of overwhelming tumor burden even though cytokine signaling for immunosuppressive regulatory T cells was down regulated. These observations suggest that the initiation of moderate exercise training for adjunctive therapeutic benefit early in the course of invasive breast cancer should be considered for further investigation.
Highlights
Epidemiological studies have revealed a protective effect of physical activity on breast cancer-related mortality in women diagnosed with breast cancer [1,2], whereby increased physical activity was associated with reduced recurrence and mortality [3]
This significant effect of voluntary wheel running on overall tumor progression was no longer evident after 4 weeks of running, the tumor sizes in the first pair of mammary glands were significantly smaller in runners compared with non-runners up until the fifth week (p = 0.03) (Figure 1C)
Our study demonstrates an early effect of voluntary wheel running on attenuating breast cancer progression in polyoma middle T oncoprotein (PyMT) transgenic mice
Summary
Epidemiological studies have revealed a protective effect of physical activity on breast cancer-related mortality in women diagnosed with breast cancer [1,2], whereby increased physical activity was associated with reduced recurrence and mortality [3]. These observations consistently suggest a potential dose-dependent effect of physical activity on breast cancer outcomes. In contrast to the anti-tumor effects presented by these studies, 9 weeks of treadmill running exacerbated mammary tumor multiplicity and reduced survival compared with sedentary controls in the p53+/2-MMTV-Wnt-1 model of mammary cancer [6]. Differences in the duration and intensity of exercise training as well as differences in murine background strains between the studies may influence tumor outcomes
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