range from further examination of elements of the biology of breast development and carcinogenesis to tests of potential interventions to reduce risk. Important components of the work recommended here provide support for the research necessary to develop better tools for assessing the carcinogenicity of chemicals and pharmaceuticals as well as tools needed to strengthen epidemiologic research. The importance of a life course perspective runs throughout these recommendations.

Many of these recommendations are directed to both researchers and research funders. Researchers will have to conduct the work described here, but they will need the resources that come from a variety of sources. The National Institutes of Health and other federal agencies are major funders of research on breast cancer or they have unique authority or responsibility in certain areas. But the nation’s portfolio of research on breast cancer is also shaped in important ways by funders and other organizations in the private sector, such as Susan G. Komen for the Cure, that have the flexibility to pursue research topics and approaches that federal agencies may not. The committee urges effective and innovative collaborations to answer the many unresolved questions about the causes of breast cancer.


Progress has been made in understanding the biology of breast development, molecular mechanisms of carcinogenesis, the influence of the tissue microenvironment on breast cancer development, and some aspects of risk and prevention. But gaps remain in understanding of the etiology of breast cancer and the extent of environmental influences on breast cancer development.

Most epidemiologic studies have been obliged to focus on events in the few years or perhaps one to two decades before a breast cancer diagnosis. As described in Chapter 5, however, growing evidence suggests that events associated with breast carcinogenesis may occur much earlier—in young adulthood, puberty, childhood, and in utero. The effect of radiation, for instance, is greater when exposure occurs around the time of puberty or earlier. Although information about some early life events, such as age when first giving birth or age at menarche, can be reliably retrieved, few studies have collected information on nonreproductive environmental exposures that may influence the occurrence of clinically detectable breast cancer many decades later.

To address gaps in knowledge about the origins of breast cancer, the committee determined that research should increasingly focus on the influence of environmental factors during potential windows of susceptibility over the life course. It is possible that some exposures later in life, after

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