ABSTRACT
This chapter considers the evidence for cancer-specific benefits and risks of physical activity and exercise. In spite of the considerable work on natural immune mechanisms against cancer, and the increasing attention to natural immune changes with exercise, the hypothesis that physical activity influences the incidence of and mortality from certain cancers consequent to the enhancement of natural immunity has not been systematically evaluated. Animal studies have focused on the exercise component of physical activity in relation to colon cancer. The chapter provides a framework for the later consideration of exercise-induced changes in natural immunity and how these may relate to cancer processes. Alternatively, exercise-induced changes in blood flow might result in greater delivery of natural killer cells, cytokines, and so on to tissue sites where tumors are proliferating; at this level, exercise would interact with the immune system to enhance cancer surveillance and decrease early tumor growth.
