from it.2 The huge burden of disease demonstrated by these numbers suggests the need for creative and innovative research and bold new approaches to uncover the intricate combination of factors, both within and outside of the body, that lead to breast cancer. The term “breast cancer” encompasses more than one disease; it is an umbrella term for several subtypes of cancer of the breast. These breast cancer subtypes differ in their clinical presentation, reveal distinct gene expression patterns, and have different genetic and molecular characteristics.3-5 The different breast cancer subtypes may have some shared as well as unique causes and contributing factors that might influence approaches to prevention.6 The strong relationship between breast cancer risk and a family history of breast cancer indicates that genetic factors play an important role in the disease.7 Most breast cancers, however, occur in people with no family history,8 so environmental factors—broadly defined—must play a major role in the etiology of the disease. Yet, preventing breast cancer by finding ways to identify and influence environmental causes of the disease has proven to be extremely challenging and has not been a priority. To identify the environmental causes of breast cancer, we must expand our knowledge about normal breast development, including changes in the breast in childhood and adolescence, and about the way that stressors in the environment alter normal breast development and influence risk for cancer, risk of a new cancer developing in the second breast, and risk of death from breast cancer. We also must expand our knowledge about interventions that could effectively reduce the impact of known risk factors for breast cancer. Many known risk factors, such as age at first menstrual period,10 cannot be easily altered to prevent this disease. Substantial evidence from randomized, controlled trials and translation research in the community, however, indicates that known, modifiable risk factors for breast cancer can be changed (i.e., increasing physical activity and Introduction We urgently need to accelerate progress toward understanding the role of the environment in breast cancer prevention. Primary, secondary, and tertiary prevention all must be considered. Primary prevention is directed at stopping the onset of a targeted condition. Secondary prevention identifies and treats asymptomatic persons who already have developed risk factors or preclinical disease but in whom the condition has not become clinically apparent. Tertiary prevention refers to the treatment and management of persons with clinical disease.9 2 CHAPTER 2-2 Breast Cancer and the Environment: Prioritizing Prevention 2 2.1 Legislation/Congressional Charge to This Committee In 2008, Congress passed Public Law (P.L.) 110-354, the Breast Cancer and Environmental Research Act.a P.L. 110-354 required the Secretary of the U.S. Department of Health and Human Services (HHS) to establish an Interagency Breast Cancer and Environmental Research Coordinating Committee (IBCERCC). The Committee mandate was to review research conducted or supported by federal agencies on environmental exposures that could influence breast cancer risk and make recommendations for innovative research strategies and opportunities to understand the role of these exposures and other factors in the context of inherent biological determinants of the disease. The Committee’s ultimate goal is to recommend research that will provide the evidence to inform, enable, and promote breast cancer intervention programs across the cancer control continuum— from prevention through detection, diagnosis, treatment, and survivorship—to reduce the burden of breast cancer. The duties of the Committee, as set forth in the authorizing legislation, are to: • Share and coordinate information on existing research activities and make recommendations to the National Institutes of Health (NIH, part of HHS) and other federal agencies regarding ways reducing weight) using cost efficient approaches.11, 12 Behavioral interventions targeting weight loss and physical activity at the individual level have shown that it is difficult for participants to maintain weight and recommended health habits. Interventions at the community, state, and national levels, such as policy changes, will be needed to achieve lasting improvements in weight and physical activity in target populations.13 In addition, medications such as tamoxifen, which can reduce the incidence of breast cancer in women at high risk of the disease, have serious side effects.14 Many women who might benefit from tamoxifen in terms of breast cancer prevention do not take this medication, in part because of these side effects.15 In spite of many unknowns and substantial obstacles to progress in understanding the environmental contributors to breast cancer, scientists are finding important clues about how the disease develops and identifying new opportunities that could lead to breakthroughs in the prevention of this complex disease. For example, investigators are learning that the timing of a person’s exposure to certain environmental factors influences breast cancer risk, and that some environmental factors affect survival from the disease. New and improved technologies to assess exposures to the mixtures of environmental contaminants and