With more than 230,000 new cases of breast cancer expected to be diagnosed in the United States in 2011, many wonder about the role that environmental exposures may be playing. Susan G. Komen for the Cure® asked the IOM to review the current evidence on breast cancer and the environment, consider gene–environment interactions, review the research challenges, explore evidence-based actions that women might take to reduce their risk, and recommend directions for future research. Overall, the IOM finds that major advances have been made in understanding breast cancer and its risk factors, but more needs to be learned about its causes and how to prevent it. The report urges a life-course approach to studying breast cancer because new information suggests that women and girls might be more susceptible to some risk factors during certain life stages.
The committee defined “environment” broadly, and reviewed evidence on a range of factors women encounter in their daily lives. Of the environmental factors reviewed, those with the most consistent evidence of a link with increased breast cancer risk included ionizing radiation, combination estrogen-progestin hormone therapy, and greater postmenopausal weight. More physical activity was linked to reduced risk. But for many other factors, the evidence from human studies is more limited, contradictory, or absent.
The IOM concludes that women may have some opportunities to reduce their risk of breast cancer through personal actions, such as avoiding unnecessary medical radiation throughout life, avoiding use of estrogen –progestin hormone therapy, avoiding smoking, limiting alcohol consumption, increasing physical activity, and, for postmenopausal breast cancer, minimizing weight gain. In addition to applying a life-course approach to studies of breast cancer, research recommendations include developing improved tools for epidemiologic research and testing of chemicals and other substances, developing effective preventive interventions, developing better approaches to modeling breast cancer risks, and improving communication about breast cancer risks. Questions about the topics addressed in the report are explored in the Questions and Answers booklet.