Epidemiological studies suggest that environmental factors may mediate the transformation of latent prostate cancer into clinically apparent tumors and that exercise appears to influence this progression. Review of recent systematic reviews, meta-analyses, and studies on the topic that have been published in the recent literature. Hypothesized biological mechanisms for the physical activity cancer association include changes in hormone level, reduced percentage of body fat, enhancement of the immune system, and alteration in free radical damage by scavenger systems. The available data indicate that 30-60 minutes per day of moderate-to-vigorous physical activity is needed to be protective against breast and colon cancers. We further identify future directions for research, including a better understanding of the biological mechanisms, the need to standardize physical activity and identify mechanistic endpoints of physical activity that can then be correlated with outcomes.