by leading authoritative bodies, and reviews the evidence on a selected set of risk factors.
As discussed in Chapters 1 and 2, the committee adopted a broad definition of “environment” that includes all factors not directly inherited through DNA. In selecting environmental factors for examination, the committee took into account several considerations, including variety in the types of potential risk factors and routes of exposure, availability of evidence for review, and indications of public concern. From the enormous list of candidates, the committee selected a limited set of factors in order to illustrate a variety of environmental exposures, and to emphasize the need for new approaches to investigate and increase the knowledge base of potential environmental risks for breast cancer. With an evolving understanding of the mechanisms for cancer development and concern about whether the right questions have yet been asked or asked using appropriate study designs, the committee saw limited value in a full review of evidence for an extensive list of environmental factors that is available from a number of other sources (e.g., International Agency for Research in Cancer [IARC], the World Cancer Research Fund/American Institute for Cancer Research [WCRF/AICR], the U.S. Environmental Protection Agency [EPA], and the National Toxicology Program [NTP]), nor was it feasible for the present study. Of the large number of environmental factors with potential but uncertain impact on breast cancer, the committee reviewed only a selected number that illustrated particular types of challenges in assessment. For example, the committee evaluated factors for which extensive epidemiologic evidence and systematic reviews were available (e.g., alcohol consumption), and it also reviewed chemicals for which studies evaluating breast cancer in humans were very limited (e.g., bisphenol A).
Little attention was given to several very familiar topics, such as dietary fat and micronutrients, that are receiving ongoing systematic review by other organizations. The committee also chose not to include established reproductive risk factors, such as age at menarche or first full-term pregnancy, and anthropometric features such as birthweight or attained height in its review of environmental factors. These risk factors have also received considerable attention elsewhere. In Chapter 7 the committee has included recommendations for additional research to confirm the appropriateness of using alterations in such reproductive and anthropometric intermediate endpoints as valid and reliable markers of alterations in risk for breast cancer.