Epidemiology and biology of physical activity and cancer recurrence

Abstract

Physical activity is emerging from epidemiologic research as a lifestyle factor that may improve survival from colorectal, breast, and prostate cancers. However, there is considerably less evidence relating physical activity to cancer recurrence and the biologic mechanisms underlying this association remain unclear. Cancer patients are surviving longer than ever before, and fear of cancer recurrence is an important concern. Herein, we provide an overview of the current epidemiologic evidence relating physical activity to cancer recurrence. We review the biologic mechanisms most commonly researched in the context of physical activity and cancer outcomes, and, using the example of colorectal cancer, we explore hypothesized mechanisms through which physical activity might intervene in the colorectal recurrence pathway. Our review highlights the importance of considering pre-diagnosis and post-diagnosis activity, as well as cancer stage and timing of recurrence, in epidemiologic studies. In addition, more epidemiologic research is needed with cancer recurrence as a consistently defined outcome studied separately from survival. Future mechanistic research using randomized controlled trials, specifically those demonstrating the exercise responsiveness of hypothesized mechanisms in early stages of carcinogenesis, are needed to inform recommendations about when to exercise and to anticipate additive or synergistic effects with other preventive behaviors or treatments.

Keywords: Biomechanisms; Cancer; Exercise; Physical activity; Recurrence.

Fig. 1

Commonly proposed mechanisms relating physical activity to cancer recurrence and/or survival. Potential additive or synergistic effects between physical activity and cancer treatment are possible

Fig. 2

Colorectal cancer serves as a useful example for studying physical activity mechanisms because risk accumulation is observable. The overall strength and consistency of epidemiologic evidence relating physical activity to colorectal cancer outcomes is strongest for colorectal cancer incidence, somewhat weaker for colorectal cancer mortality (given fewer prospective studies; although results have been relatively consistent, generally showing benefit from both pre- and post-diagnosis physical activity), and weakest for adenoma (polyp) recurrence, due to limited epidemiologic research focused on recurrence outcomes and studies showing significant associations only in men. Solid arrows indicate known pathways. Broken arrows indicate hypothesized pathways. ACF, aberrant crypt foci; PA, physical activity