 exercise has been shown to improve postischemia perfusion of normal tissues ; we investigated whether these effects extend to solid tumors . 
 estrogen receptor  negative ( er- , 4t1 ) and er+ ( e0771 ) tumor cells were implanted orthotopically into syngeneic mice ( balb / c , n = 1112 per group ) randomly assigned to exercise or sedentary control . 
 tumor growth , perfusion , hypoxia , and components of the angiogenic and apoptotic cascades were assessed by mri , immunohistochemistry , western blotting , and quantitative polymerase chain reaction and analyzed with one - way and repeated measures analysis of variance and linear regression . 
 all statistical tests were two - sided . 
 exercise statistically significantly reduced tumor growth and was associated with a 1.4-fold increase in apoptosis ( sedentary vs exercise : 1544 cells / mm2 , 95% ci = 1223 to 1865 vs 2168 cells / mm2 , 95% ci = 1620 to 2717 ; p = .048 ) , increased microvessel density ( p = .004 ) , vessel maturity ( p = .006 ) and perfusion , and reduced intratumoral hypoxia ( p = .012 ) , compared with sedentary controls . 
 we also tested whether exercise could improve chemotherapy ( cyclophosphamide ) efficacy . 
 exercise plus chemotherapy prolonged growth delay compared with chemotherapy alone ( p < .001 ) in the orthotopic 4t1 model ( n = 17 per group ) . 
 exercise is a potential novel adjuvant treatment of breast cancer . 
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