Physical Activity and Cancer
The 2002 International Agency on Research Against Cancer Report, Weight Control and Physical Activity, indicated that physical activity is likely to have a substantial preventive effect for cancers of the colon and breast. In addition, research is expanding on the role of physical activity in improving the quality of life among cancer patients and cancer survivors, and on its potential beneficial effect on prognosis and survival. Several studies within the SEER registry program have contributed to this body of evidence. Two population-based studies using participants from the Los Angeles Cancer Surveillance Program revealed that physical activity greatly reduces the risk for colon cancer in men and breast cancer in women. In addition, a collaborative effort across SEER registries in the Los Angeles County area, New Mexico, and Seattle is examining the combined effects of physical activity, weight, and diet on breast cancer prognosis.
Researchers selected 2,950 men diagnosed with colon cancer and categorized them according to occupation, grouped by level of activity involved in the job: sedentary, moderately active, or highly active. The study demonstrated that colorectal cancer risk increased as activity level decreased. This gradient was consistent for all socioeconomic factors, for whites, blacks, immigrant and native Hispanics, and for each subsection of the colon. The effect of physical activity on the colon is consistent with the evidence supporting dietary influence on the causes of cancer and other diseases, and the researchers urged further study of dietary effects on cancer risk.
The breast cancer case-control study conducted by the Los Angeles SEER registry evaluated the effects of physical exercise on breast cancer risk in women aged 20-40 years. In all cases, controlling for numerous variables, the risk of breast cancer significantly declined with increasing amounts of lifetime physical exercise. The investigators proposed that habitual physical activity can alter menstrual function, which reduces the cumulative exposure to the carcinogenic effects of progesterone and estradiol.
The HEAL (Health, Eating, Activity and Lifestyle) Study of Breast Cancer Prognosis is examining the effect of physical activity, weight, and diet on breast cancer prognosis among a multiethnic cohort of women with early stage breast cancer. Initial results from this study have found that physical activity levels were reduced significantly after patients were diagnosed with breast cancer. Greater decreases in physical activity were observed among women who were overweight at the time of diagnosis of breast cancer. These results suggest that declines in physical activity may contribute to weight gain commonly experienced during breast cancer treatment, which has been found to have an adverse effect on prognosis.
Garabrant DH, Peters JM, Mack TM, Bernstein L. Job activity and colon cancer risk. Am J Epidemiol 1984;119:1005-1014.
Bernstein L, Henderson BE, Hanisch R, Sullivan-Halley J, Ross RK. Physical exercise and reduced risk breast cancer in young women. J Natl Cancer Inst 1994;86:1403-1408.
Irwin ML, Crumley D, McTiernan A, Bernstein L, Baumgartner R, Gilliland FD, Kriska A, Ballard-Barbash R. Physical activity levels before and after a diagnosis of breast cancer: The Health, Eating, Activity, and Lifestyle (HEAL) Study. Cancer 2003; 97:1746-1757.