Physical exercise — either as an interventional program or as a self-reported recreational activity — is considered to be generally beneficial for not only the general population, but also among patients receiving treatment for cancer and into survivorship.1
The mechanisms that drive this benefit are not well-understood, and it is believed that the benefit is not just a result of reducing risk factors such as body weight.2 Though not based on direct evidence, there are several hypotheses of how exercise can modulate cancer outcomes, including influencing metabolic and sex steroid hormone levels, increasing immune surveillance, decreasing systemic inflammation, and reducing oxidative damage.3
Mortality and Other Outcomes
Several meta-analyses suggest that exercise improves survival outcomes among patients with cancer. A meta-analysis of 71 cohort studies that included 3,985,164 subjects from the general population and 66,995 patients with cancer found a nonlinear dose-response relationship between exercise and cancer mortality in the general population, with benefit occurring with 5 metabolic equivalents of task (MET)-hours per week.4 High levels of physical activity were associated with significantly improved cancer-specific mortality among the general population (hazard ratio [HR], 0.83; 95% CI, 0.79-0.87) and cancer survivors (HR, 0.78; 95% CI, 0.74-0.84).
Similar results were found specific to breast and colorectal cancers. A meta-analysis of 22 cohort studies that included 123,574 patients with breast cancer found that high lifetime exercise levels prediagnosis were significantly associated with lower all-cause (HR, 0.82; 95% CI, 0.70-0.96) and breast cancer-related mortality (HR, 0.73; 95% CI, 0.54-0.98) compared with low or no exercise.5 High levels of physical activity more recent, but still prior, to the diagnosis also improved all-cause (HR, 0.73; 95% CI, 0.65-0.82) and breast cancer-related mortality (HR, 0.84; 95% CI, 0.73-0.97) compared with low or no exercise. High levels of exercise recently after diagnosis conferred a greater survival benefit for both all-cause (HR, 0.52; 95% CI, 0.43-0.54) and breast cancer-specific mortality (HR, 0.59; 95% CI, 0.45-0.78). There was also a significant reduction in breast cancer events, which included progression, new primaries, and recurrence, associated with high exercise levels before (HR, 0.72; 95% CI, 0.56-0.91) and after diagnosis (HR, 0.79; 95% CI, 0.63-0.98). Similarly, a meta-analysis of 11 studies that included 17,295 patients with colorectal cancer found that prediagnosis physical activity significantly improved overall (relative risk [RR], 0.81; 95% CI, 0.72-0.91) and colorectal cancer–specific mortality (RR, 0.79; 95% CI, 0.71-0.89).6 Postdiagnosis exercise also significantly improved overall (RR, 0.77; 95% CI, 0.63-0.94) and colorectal cancer̶specific mortality (RR, 0.71; 95% CI, 0.63-0.81).
In addition, there was a small trial that randomly assigned 103 patients undergoing allogenic stem cell transplant to an exercise intervention or control group.7 The intervention included endurance exercise 3 to 5 days a week and resistance exercise 2 days a week, which was initiated 1 to 4 weeks prior to hospital admission and continued for up to 8 weeks after hospital discharge. The exercise group demonstrated a significantly lower total mortality at 12.0% compared with 28.3% in the control group (P = .03) and trended toward a lower nonrelapse mortality rate (4.0% vs 13.5%; P = .086).
The benefit of exercise on other cancer outcomes was less clear. A trial of 122 patients with lymphoma found no significant difference in progression-free survival with supervised aerobic exercise compared with the control group, but there was a trend toward benefit (68.5% vs 59%, respectively; HR, 0.70; 95% CI, 0.35-1.39).8 A systematic review of 4 randomized controlled trials found that resistance training with or without aerobic exercise did not affect prostate-specific antigen levels among men with prostate cancer.9