Rapamycin increases breast tumor burden in young wheel-running mice.

Rapamycin is an immunosuppressive and anti-cancer drug recently shown to enhance healthy aging in animal models. Regular physical exercise is associated with healthy aging and reduced risk of age-related diseases, such as cancer. In order to test the combined effect of these approaches, mice with 4T1 breast cancer were fed rapamycin at 14 ppm and allowed access to voluntary running wheels. After 17 days of treatment, mice fed the rapamycin diet that ran showed a significant increase in tumor burden compared with mice that did not run (P = 0.017). Not only does this have implications for young breast cancer patients, but suggests that combining rapamycin and exercise as an anti-aging strategy at a young age might be contraindicated.