February 28 - 29, 2008 Advisory Committee Meeting Minutes
Subcommittee Report: Cancer
Anne McTiernan, M.D., Ph.D., presented the cancer subcommittee work. The subcommittee focused on 2 areas: Physical activity effect on cancer risk and the role of physical activity in cancer survivorship. The goals of the subcommittee included:
Determine evidence of dose-response of physical activity and cancer.
Identify subgroups of individuals that may differ on physical activity effect on cancer risk.
Review independent and combined effects of overweight/obesity and physical activity on cancer risk.
Identify mechanisms that may explain links between physical activity and cancer risk, to help determine validity of associations, and to help with guidance on exercise prescriptions.
The data that was reviewed focused on cancer risk by specific cancer subtypes. Most of the data is on breast and colorectal cancer. From the studies the following risk reductions to cancer associated with physical activity were extrapolated:
Breast cancer — 20 – 80% risk reduction
Colon cancer — 30% risk reduction
Edometrium cancer — 30% risk reduction
Lung cancer — 20 – 24% risk reduction
Prostate cancer — no effect
Ovary cancer — 19% risk reduction
Other cancers — insufficient evidence
The data also suggests there are no clear subgroups that differ from overall physical activity cancer associations. Physical activity also reduces cancer risk independent of weight control, but optimal effect may be seen with optimal weight maintenance. Additionally, there is no clear dose cut-off for physical activity effect across different cancer types.
There is a dose-response effect between physical activity and colon and breast cancer, showing 30 – 60 minutes of moderate-to-vigorous activity per day reduces risk. In other cancers there is insufficient evidence to support any conclusions. Regular aerobic exercise is associated with reduced risk for several cancers. Benefits are seen with moderate intensity exercise; however, greater benefit can be seen with greater volume and intensity. The benefit is also seen across age and avoiding lifetime weight gain will likely optimize benefits.
Additional questions that current data cannot sufficiently answer include the effects of specific activities, the optimal dose(s) of the activity and the optimal time of life for benefits.
Addressing the issue of the effects of physical activity on cancer survivors, Dr. McTiernan noted that there are over 10 million U.S. cancer survivors with length of survival increasing. Cancer survivors face long-term effects of their cancer, treatments, and risk for future cancer and other chronic disease. The evidence of benefit varies from preliminary to moderate to strong in different cancer types in different domains.
There are several plausible mechanisms in this area. Human trials support the effect of exercise on improving risk factors/biomarkers for cancer among adipose tissue and cytokines, sex hormones, insulin and insulin resistance, and inflammation. The greatest effect in serum biomarkers is seen with reduction in body fat.
The American Cancer Society issues the following recommendations:
Reducing cancer risk in adults
Moderate-vigorous activity for at least 30 minutes per day, per week; however, 45 – 60 minutes per day is preferable.
Reducing cancer risks in children
Moderate-vigorous activity for at least 60 minutes or more per day, per week.
Reducing cancer risks in patients and survivors
When on treatment, physical activity is likely helpful; however reduced intensity may be needed.
When off treatment one can participate in activity as one would when in prevention mode.
Regarding future research needs more information is needed on the associations of physical activity with less well-studied cancers as well as in minority populations. Additional information is also needed on the effects of specific types of activity as well as different intensity, duration and frequency of activity. Future research should focus on long-term observational follow-up of survivors. There is not enough data to comment on the dose-response effect of physical activity on recurrence and mortality as well as effect on early late stages of cancer. More studies are needed on the effects of physical activity on specific cancer treatments.
The subcommittee can conclude that 30 – 60 minutes per day of moderate-to-vigorous endurance exercise reduces the risk for colon and breast cancers. There is insufficient data to give clear dose recommendations for other cancers. Exercise programs improve quality of life and fitness in cancer survivors.
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