This document summarizes evidence from studies on the mechanisms by which physical activity may impact cancer risk and discusses results from intervention trials measuring relevant biomarkers. It finds that exercise interventions significantly reduce levels of inflammation, oxidative stress, and hormones like leptin, especially with weight loss. Studies in adipose tissue suggest effects on gene expression related to inflammation and sex steroids. While effects on immunity and DNA repair are less clear, more research is needed in cancer patients to understand impacts on prognosis. Future interdisciplinary studies should address multiple dimensions of energy balance and biomarkers.