Centre of Physical Activity Research, Copenhagen University Hospital
The benefits of engaging cancer patients in an active lifestyle despite their disease are becoming increasingly evident. At present, more than 100 exercise intervention studies in cancer patients have reported favorable effects on both patient-reported outcomes and physical functioning when exercise is performed during, or after anti-neoplastic therapy. In addition, accumulating evidence suggests that exercise has a direct effect on tumor growth. Early evidence from observational studies has shown that physical activity reduces the risk of disease recurrence in colorectal, prostate and breast cancer patients. In line with this, we have recently shown that voluntary wheel running in mice could control tumor growth through an exercise-dependent increase in intratumoral immune cell infiltration in various genetic and transplantable murine tumor models. Intratumoral infiltrates included natural killer (NK cells), and exercise-mediated induction of intratumoral NK cells contributed to a 50-60% reduction in tumor growth. Further mechanistic analyses demonstrated that tumor control could be achieved through an epinephrine-dependent mobilization of NK cells, together with subsequent IL-6-induced redistribution and activation of NK cells. These findings linked exercise, epinephrine and IL-6 to NK cell mobilization and redistribution, and ultimately, to control of tumor growth in mice.