Senior investigator Lee Jones of Duke Comprehensive Cancer Center and colleagues implanted prostate tumors subcutaneously in the flanks of 50 mice and then put half of the mice in cages with exercise wheels and half in cages with no wheels. All mice were fed the same diet. On average, the exercising mice ran more than one-half a mile each day.

"Our study showed that exercise led to significantly greater tumor growth than a more sedentary lifestyle did, in this mouse model," Jones said in a statement.

The findings were presented at the American Association for Cancer Research annual meeting in San Diego.

The researchers caution men against interpreting these findings as an endorsement for not exercising for fear of getting or exacerbating cancer.

"These mice were not receiving treatment and we were allowing aggressive tumors to grow unchecked for the sake of the experiment," study investigator Stephen Freedland said. "Patients would not find themselves in the same situation."