December 6 - 7, 2007 Advisory Committee Meeting Minutes
Cancer Subcommittee Report
Anne McTiernan, M.D., thanked the other member of the subcommittee, I-Min Lee, M.D., and their consultant, Dr. Katie Schmitz, with assistance from her pre-doctoral student, Rebecca Speck, and their CDC liaison, Candace Rutt. The subcommittee's focus has been to look at physical activity effect on cancer risk and the role of physical activity in cancer survivorship.
The subcommittee formulated three research questions:
What are the associations between physical activity and incidents of specific cancers?
What are the mechanisms explaining the associations between physical activity and cancer and how does physical activity relate to cancer independently of its effects on overweight and obese individuals?
What are the effects of physical activity on cancer survivors, including long-term and late effects of treatment, quality of life, and prognosis?
Cancer is not a specific disease as every type of cancer is different. Because of this fact different cancers had to be looked at separately with a focus on cancers that had been studied in terms of physical activity. The most studied include, breast, prostate, colon and rectum with a majority of the data from breast, prostate and colon. The subcommittee's goals were to determine the evidence of dose-response of physical activity in cancer and to identify subgroups that may differ on physical activity effect and cancer risk. Also, the group reviewed the independent and combined effects of overweight individuals and any relationship between physical activity and cancer risk.
The majority of the data reviewed was epidemiological data through 2001. A preponderance of the data suggests that colon cancer in particular is reduced in risk with increasing physical activity. Studies that combine colon and rectal cancer do not show the same protective benefits. Two-thirds of the studies show reduced risk of breast cancer with increased physical activity. The data for prostate cancer seems to initially suggest that there is no benefit of reduced risk. Reviewing the Women's Health Initiative beneficial effects in reduced risk of breast cancer were found in subjects with lowest BMI. In looking for special subgroups that had differing levels of risk no consistent pattern was found.
Dr. McTiernan introduced Dr. Schmitz who reviewed the subcommittee's work on cancer survivors. In studying this issue three types of outcomes were of particular interest: prognosis or reoccurrence and mortality among survivors, long-term and late effects of treatment and quality of life.
The data on cancer reoccurrence is limited as there were only three studies in the literature. Review of this limited data did show a dose-response effect for individuals that did activity equivalent to walking three to six hours per week.
An additional set of outcomes the subcommittee dealt with focused on the effects of cancer treatment. For purposes of the group's work only individuals that had completed cancer treatment were researched in order to focus on the effects of physical activity among cancer survivors and how it relates to possible benefits in their quality of life. The data suggests that physical activity may be useful for the growing population of adult cancer survivors who are preventing reoccurrence and mortality in a dose-response manner and improving long-term or late effects of treatment. It also appears that both aerobic and resistance training would be useful to improve these outcomes. It is unclear if aerobic activity has more benefit than resistance training or vice-versa. These conclusions are based only on adult cancer survivors, as there is not enough data to address childhood cancer survivors.
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