Vigorous Exercise May Reduce Mortality in Adult Survivors of Childhood Cancer

While it is well understood that, in the general population, regular exercise is associated with a reduced risk of death, less is known about whether exercise is similarly beneficial for adult survivors of childhood cancer who may already have an increased risk of death and a shortened life expectancy because of late effects of treatment, including subsequent malignant neoplasms and cardiovascular disease (CVD). A study newly published in JAMA Oncology sought to evaluate whether vigorous exercise can change mortality in this population.

The retrospective cohort study of adult survivors who participated in the Childhood Cancer Survivorship Study (CCSS) followed 15,450 patients who were diagnosed and treated at 27 locations in the United States and Canada between January 1970 and December 1999.

At baseline and at follow-up, enrollees were asked to report how many days in the prior week they had engaged in vigorous exercise (exercise that was sufficient to result in heavy breathing, sweating, or increased heartrate). Self-reported exercise was converted into an average of metabolic equivalent tasks (METs), in hours per week, by the investigators. MET-hours per week were then categorized into 4 groups: 0, 3 to 6, 9 to 12, and 15 to 21.

The researchers found that vigorous exercise exposure greater than 0 MET-hours per week was associated with a significant reduction in the incidence of all-cause, relapse-related, and health-related mortality. At year 15, the group with 0 MET-hours per week had an incidence of all-cause mortality of 11% (95% CI, 10.6%-12.8%). By comparison, the other groups had the following incidence of all-cause mortality:

• 3 to 6 MET hours per week: 8.6% (95% CI, 7.4%-9.7%)
• 9 to 12 MET hours per week: 7.4% (95% CI, 6.2%-8.6%)
• 12 to 21 MET hours per week: 8.0% (95% CI, 6.5%-9.5%)

Compared to the group with no exercise, the adjusted risk ratio (RR) was 0.81 (95% CI, 0.68-0.97) for the 3— to 6–MET-hour group, 0.82 (95% CI, 0.68-1.00) for the 9– to 12–MET-hour group, and 0.79 (95% CI, 0.62-1.00) for the 15– to 21–MET-hour group. Exercise exposure of 15 to 18 MET-hours per week, which could be divided into sessions of 60 minutes per day, 5 days per week, appeared to be optimal.

Additionally, survivors who increased their exercise over time continued to reduce their risk of mortality; increased exercise exposure over 8 years was associated with an adjusted 40% reduction in the rate of all-cause mortality, compared with maintaining a low level of exercise (RR, 0.60; 95% CI, 0.44-0.82).

The authors say that their findings significantly extend the current evidence base and provide epidemiological evidence to support endorsing exercise for cancer survivors, though they warn that, because observational studies are susceptible to reverse-causation bias, the results must be interpreted with caution. At a minimum, they suggest that the study supports counseling all cancer survivors, as appropriate, to increase participation in vigorous exercise at least once per week, as such an increase may be realistic and achievable for a significant proportion of survivors.

References

Scott JM, Li N, Liu Q, et al. Association of exercise with mortality in adult survivors of childhood cancer [published online June 3, 2018.] JAMA Oncol. doi: 10.1001/jamaoncol.2018.2254.