Behavioral Risk Factors in Breast Cancer: Can Risk Be Modified?
Cancer Prevention Research Program, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA; Department of Epidemiology, School of Public Health and Community Medicine and Department of Medicine, School of Medicine, University of Washington, Seattle, Washington, USA
Correspondence: Anne McTiernan, M.D., Ph.D., Cancer Prevention Research Program, Fred Hutchinson Cancer Research Center, P.O. Box 19024, MP-900, Seattle, Washington 98109-1024, USA. Telephone: 206-667-7979; Fax: 206-667-7850; email@example.com
The International Agency for Research on Cancer estimates that 25% of breast cancer cases worldwide are due to overweight/obesity and a sedentary lifestyle.
The preponderance of epidemiologic studies indicates that women who engage in 3–4 hours per week of moderate to vigorous levels of exercise have a 30%-40% lower risk for breast cancer than sedentary women. Women who are overweight or obese have a 50%-250% greater risk for postmenopausal breast cancer.
Alcohol use, even at moderate levels (two drinks per day) increases risk for both premenopausal and postmenopausal breast cancer. Certain dietary patterns, such as high fat, low vegetables/fruits, low fiber, and high simple carbohydrates, may increase risk, but definitive data are lacking.
These lifestyle factors are likely associated with breast cancer etiology through hormonal mechanisms. The worldwide trends of increasing overweight and obesity and decreasing physical activity may lead to an increasing incidence of breast cancer unless other means of risk reduction counteract these effects.
Thus, adoption of lifestyle changes by individuals and populations may have a large impact on the future incidence of this disease.
That lifestyle changes can change the risk of developing breast cancer is supported by several lines of evidence. First, rates of breast cancer incidence vary widely by geographic areas around the world.
Only a small part of these differences is due to genetics, few chemical or other carcinogen exposures have been linked to risk, and the remainder of cases are, therefore, due to individual health and lifestyle behaviors .
Second, within-country changes over time in breast cancer incidence have been paralleled by great lifestyle and health behavior changes . Third, experimental animal and human models provide confirmation of observable effects of several lifestyle behaviors on breast biology .
The International Agency for Research on Cancer estimates that 25% of breast cancer cases worldwide are due to overweight/obesity and a sedentary lifestyle . An American Cancer Society cohort study of 495,477 women followed for 16 years found that the risk of breast cancer mortality increased significantly with increasing level of obesity; compared with women with a body mass index (BMI) under 25.0, those with BMIs of 25–29.9, 30–34.9, 35–39.9, and 40 had relative risks (RR) of breast cancer mortality of 1.34, 1.63, 1.7, and 2.12, respectively .
Thus, lifestyle changes to correct these factors might be expected to have a major impact on public health.
Most breast cancer prevention strategies involve some amount of behavioral change. Tamoxifen therapy to prevent breast cancer , for example, involves a behavioral change on the part of the individual.
The implementation of this prevention method, therefore, depends on the individual being willing to change her daily routine to include taking this medication. Similarly, compliance with recommended breast cancer screening guidelines involves adopting behaviors.
Self-exam of the breast requires frequent monitoring behaviors; undergoing mammography and clinical breast exams involve making and keeping clinic appointments. While these and other prevention methods require a great deal of behavioral change, a discussion of all of these is beyond the scope of the present paper.
The purpose of this paper is to outline behavioral strategies that show promise in the prevention of breast cancer. It covers the following major lifestyle behaviors that are relevant to breast cancer etiology and control: physical activity, weight control, diet, and alcohol use. This paper, however, does not review the implementation of behavioral changes.
The Oncologist, Vol. 8, No. 4, 326–334, August 2003
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