Hormones, Hormone Metabolism, Environment, and Breast Cancer:
A Workshop of the National Action Plan on Breast Cancer's Etiology Working Group

Devra Lee Davis¹ and Susan M. Sieber²

¹World Resources Institute, Washington, DC; ²National Cancer Institute, Bethesda, Maryland

-- Environ Health Perspect 105(Suppl 3):557 (1997)

For more than 200 years, scientists have appreciated that breast cancer cannot arise without hormonal influences. In the 18th century, the pioneering researcher on environmental medicine, Bernardo Ramazzini, observed that nuns had higher rates of breast cancer and speculated that this might be tied to the fact that they did not have children. A century later, Beatson reported that mammary cancer did not occur in rodents that had their ovaries removed. More recently, modern epidemiologic studies have found that most of the known risk factors for breast cancer, except radiation, can be tied to lifetime exposure to estradiol and other hormones. Thus, the earlier in life that menses begins and the later that it ends, the greater cumulative exposure to estradiol and the risk of breast cancer.

While the importance of hormones for breast cancer has been understood for some time, only recently has attention focused on the need to develop and validate standardized methods for measuring hormones directly and for assessing the mechanisms by which they affect breast cancer and other aspects of women's health. In addition, several investigators have proposed that environmental factors, such as xenoestrogens and other xenohormones, may alter hormonal metabolism and thereby contribute to the development of breast cancer. As most cases of breast cancer occur in women with few of the established risk factors, efforts to identify new risk factors and new protective factors must continue to rank as high priority.

Recognizing the critical importance of hormones and environmental factors for breast cancer, this workshop brought together key multidisciplinary researchers in this field to assess the state of the art regarding the measurement and metabolism of hormones, the effect of environmental factors on hormone metabolism, their roles in the development of breast cancer, and major research gaps and data needs. The workshop also sounded the clarion call of activists, insisting that researchers do a better job communicating their results and developing research agendas that pay more attention to the identification of avoidable factors.

In response to a petition to President Clinton from 2.6 million people urging that there be a new national strategy to fight breast cancer, the Secretary of Health and Human Services, Donna Shalala, announced the development of a National Action Plan on Breast Cancer (NAPBC), which is a public/private partnership coordinated by the U.S. Public Health Service's Office on Women's Health. The mission of the NAPBC is to stimulate rapid progress in eradicating breast cancer.* Spearheaded by contributions from more than 200 scientists and activists, the NAPBC organized itself into six areas of focus, including a working group on breast cancer etiology. Reflecting the concerns of activists and scientists, the Etiology Working Group of the NAPBC convened and organized this meeting, together with the National Cancer Institute, Tulane University's Center for Bioenvironmental Research, and the U.S. Public Health Service's Office of Women's Health. The meeting followed a standard scientific format, featuring key presenters and responders. Activists attended the meeting and provided penetrating commentary both on the scientific issues that were discussed and on additional policy issues that need to be addressed in the future. Papers presented at this meeting reviewed the state of the art regarding hormonal metabolism, environmental factors and breast cancer, and avoidable or preventable causes of breast cancer. Recognizing the rapidly evolving nature of the science undergirding these issues, the organizing committee encouraged the editor to seek late-breaking additional contributions from researchers who were not able to present them to the meeting.

Recent developments provided in this volume and elsewhere indicate the complexities of the issue. Women are typically exposed to mixtures of xenohormones that include both beneficial and harmful materials, making human studies to detect these impacts especially difficult. Some xenoestrogens, such as DDT, appear to be harmful, while others, such as phytoestrogens like those found in soy products and perhaps dioxin, appear to be protective. In addition, some new studies not reviewed in this issue implicate other avoidable causes of breast cancers, including passive and active smoking, alcohol drinking, and lower levels of exercise, vitamin D, calcium, and perhaps melatonin. The role of prenatal exposures could prove to be critical and extremely difficult to study.

This monograph provides most of the key papers that were presented at the workshop, but does not include the lively discussions that occurred with each presentation. There was consensus that the development of validated and repeatable methodologies for measuring steroid hormones (including xenohormones) is urgently needed. Questions about the reliability and validity of past and current hormone measurement techniques were extensively considered at the meeting and remain the proper subject of continued research and speculation. Persisting controversies and differences of opinion regarding many of the subjects covered in this monograph reflect the healthy give and take of science at the cutting edge. The organizing committee believes that clearly articulated research opportunities outlined in these papers offer a road map for all those in the public and private sectors concerned with improving the scientific understanding of breast cancer, hormones and the environment.

*For more information, contact the U.S. Public Health Service, Office on Women's Health, Department of Health and Human Services, 200 Independence Ave, SW, Room 722F, Washington, DC 20201. Telephone: (202) 401-9587.

Last Update: April 7, 1997