Chapter 01 - Safeguarding Exercise Capacity Throughout and After Cancer Treatment
Sufficient levels of physical activity may also be important to improve disease-free and overall survival. Observational studies showed that higher levels of moderate-to-vigorous physical activity were associated with lower mortality risk in survivors of breast, colon, and prostate cancer, with physically active survivors having approximately 50% lower mortality. However, to establish a causal relationship between physical activity and survival, additional RCTs are needed.
RCTs evaluating the effects of physical activity on biomarkers related to cancer prognosis have recently been summarised by Ballard-Barbash and colleagues. The results suggest that exercise may result in beneficial changes in circulating levels of insulin, IGF-1, and IGF-1 binding proteins in breast cancer survivors. There is also evidence that exercise leads to beneficial changes in circulating levels of C-reactive protein and in natural killer cell cytotoxic activity in cancer survivors, including breast, prostate, and gastric cancer. In prostate cancer survivors, there is consistent evidence that exercise does not increase prostate-specific antigen (PSA) or testosterone levels. Evidence for other biomarkers is limited or non-existent. Also, the mediating role of immune, endocrine, or musculoskeletal systems on the effects of exercise on cancer outcomes requires further investigation.
Furthermore, the interaction between physical activity and primary cancer treatment remains unclear. In the START trial, Courneya and colleagues found chemotherapy completion rates to be higher in patients who completed a resistance exercise programme during adjuvant chemotherapy treatment for breast cancer (89.8%), compared to a usual care control group (84.1%) or an aerobic exercise group (87.4%). This resulted in higher survival rates among the exercise groups compared to the control group.
In addition to observational data on survival and experimental data on biomarkers in cancer survivors, a few studies in animals suggested that exercise may inhibit tumour growth, but others did not. At present, further investigation on the effects of physical activity on chemotherapy completion rates and tumour growth is needed.