Effects of exercise on the immune response to cancer.

This study examined the effects of two doses of exercise on tumor incidence and progression, and the number and activity of intratumoral phagocytic cells (80% macrophages [M phi's]). Male mice were randomly assigned to control (CON), moderate (MOD) or exhaustive (EXH) treadmill running. Mice were inoculated subcutaneously with 2.5 x 10(5) mammary adenocarcinoma cells after 3 d of running (3 h after the last run at a point when enhancement in M phi cytotoxicity is observed). This tumor was chosen due to its susceptibility to M phi inhibition in vitro and in vivo. Mice continued daily running for 14 d. Food intakes were higher during the last 3 d in MOD and EXH, but body weights were no different. Flow cytometer analysis of tumor masses revealed that MOD had greater numbers of phagocytic cells (vs EXH) with slightly higher phagocytic activities (vs CON and EXH) (P < 0.05). However, no group differences in tumor appearance were seen except on day 7 when CON had less observable tumors than MOD and EXH (P < 0.05). Tumor size was also not different between groups at any point. These results indicate that moderate exercise can increase the phagocytic capacity of intratumoral phagocytic cells, but these changes had no apparent effect on tumor incidence or progression in this study.