elucidated. In this study, tumor-bearing mice randomized to voluntary wheelrunning showed over 60% reduction in tumor incidenceand growth across five different tumormodels.Microarray analysis revealed training-induced upregulationof pathways associated with immune function.NK cell infiltration was significantly increasedin tumors from running mice, whereas depletion ofNK cells enhanced tumor growth and blunted thebeneficial effects of exercise. Mechanistic analysesshowed that NK cells were mobilized by epinephrine,and blockade of b-adrenergic signaling bluntedtraining-dependent tumor inhibition. Moreover,epinephrine induced a selective mobilization of IL-6-sensitive NK cells, and IL-6-blocking antibodiesblunted training-induced tumor suppression, intratumoralNK cell infiltration, and NK cell activation.Together, these results link exercise, epinephrine,and IL-6 to NK cell mobilization and redistribution,and ultimately to control of tumor growth.