December 6 - 7, 2007 Advisory Committee Meeting
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
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.