Breast cancer incidence has been increasing about 1 percent per year for the past sixty years, and rose by more than 40 percent between 1973 and 1998. Only 30 percent of breast cancer cases are attributed to the generally accepted risk factors. Only 5-10 percent of breast cancer cases involve mutations on the so-called breast cancer genes. And the longer immigrant women live in the U.S. the more likely they are to get breast cancer. These trends suggest that a complex intersection of factors is at work in breast cancer causation, both internal and external environments.

International, national, state, and community-based organizations have been evaluating the role of environmental exposures for decades.

The U.S. National Toxicology Program (NTP) has identified substances and exposures that are known or suspected to cause cancer, including: naturally occurring exposures (ultraviolet light, radon gas, infectious agents, etc.); medical treatments (chemotherapy, radiation, immune system-suppressing drugs, etc.); workplace exposures; household exposures; pollution; and lifestyle factors.

The Strategy and Implementation Plan for the International Agency for Research on Cancer (IARC) states that, “The environment (defined in its broadest sense to include lifestyle, nutrition and occupation, in addition to physical, chemical and biological factors), plays a role in the overwhelming majority of cancers and consequently, at least in principle, the majority can be prevented. However, despite advances in identifying a number of major human carcinogens there remain a significant proportion of cancers for which the etiology is unclear.”

In 2003, the Breast Cancer and the Environment Research Program (BCERP), a joint effort funded by National Institute of Environmental Health Sciences (NIEHS) and the National Cancer Institute began studying the impact of prenatal-to-adult environmental exposures that might predispose a woman to breast cancer. NIEHS concludes that, “Most experts agree that breast cancer is caused by a combination of genetic, hormonal, and environmental factors.” After seven years of research the NIEHS stated:

“Reports are already pointing to weak relationships between exposure to these endocrine disruptors and the early onset of puberty. This factor may be one of the pieces in the complex puzzle that alters risk of breast cancer. Further studies are under way within the BCERP to understand the impact of indoor pesticides, heavy metals, diet, pregnancy, and hormone-like substances found in cosmetics and sunscreen.”

The largest state-funded research effort in the U.S., the California Breast Cancer Research Program, was established in 1993 also based on the premise that environmental factors play an important role in cancer development.

Community-based organizations such as the Silent Spring Institute founded in 1993 also argue that the rise in breast cancer incidence is not surprising given the amount of synthetic chemicals that entered the marketplace after World War II, which contain chemical carcinogens known to damage DNA, promote tumor growth, and increase the carcinogenic susceptibility of mammary glands.

The Breast Cancer Fund‘s seminal report, State of the Evidence (6th ed.), continually reviews the body of research about the timing of toxic exposures, low-dose exposures at environmentally significant levels, real-life mixtures of exposures; and the complexity of interactions between environmental and other risk factors for breast cancer.  The NIEHS links to the Breast Cancer Fund’s State of the Evidence report on its web page as a key resource.

There is a body of evidence suggesting environmental links to breast cancer. At the same time, toxic exposures do not usually cause disease single-handedly, save for intense acute exposures. What’s more likely is that there is a delicate balance among exposures over time, accumulated genetic changes resulting from exposures, protective factors, susceptibility, disease heterogeneity, and differing mechanisms of action brought upon by chemical compounds. Together, these set the conditions, or not, for cancer. The mechanisms are not clear cut. What is clear is that the environment matters.

Concerned About Fracking

HF ImageWithin the last decade, the combination of hydraulic fracturing (fracking) with horizontal drilling has initiated large-scale drilling for natural gas across the United States. In this series, we explore some of the many reasons advocates are concerned about the impact of fracking on human health and the environment.

Evidence linking cancer and the environment is plentiful. Here is a short list (alphabetical):

Asturias Declaration: A Call for Action (2011) – The International Agency for Research on Cancer (IARC) supports and endorses the Asturias Declaration, which calls for the primary prevention of environmental and occupational cancer in countries around the world. IARC scientists worked closely together with colleagues at World Health Organization to develop the scientific programme and to draft the Asturias declaration, a call for action.

Consensus Statement on Breast Cancer and the Environment (Breast Cancer Working Group of the Collaborative on Health and the Environment, 2006) – Concludes that research has made clear that breast cancer and other cancers result from a complex web of causation in which multiple factors interact.

Disease Clusters Spotlight the Need to Protect People from Toxic Chemicals (by Kathleen Navarro, Sarah Janssen, MD, PhD, MPH, Terry Nordbrock, MLS, MPH, Gina Solomon, MD, MPH) – An unusually large number of people sickened by a disease in a certain place and time is known as a ‘disease cluster’. Clusters of cancer, birth defects, and other chronic illnesses have sometimes been linked to chemicals or other toxic pollutants in local communities, although these links can be controversial. There is a need for better documentation and investigation of disease clusters to identify and address possible causes. Published by the Natural Resources Defense Council.

Identifying Gaps in Breast Cancer Research (Julia G. Brody, PhD, Marion H.E. Kavanaugh-Lynch, MD, MPH , Olufunmilayo I Olopade, MD, Walter L. Palmer Distinguished Service Professor of Medicine, Susan Matsuko Shinagawa, Sandra Steingraber, PhD, David R. Williams, PhD, 2007) – a review of existing research—gathered from widely scattered sources—pointed toward discovering research areas that show some connection with the disease, and recommending further investigations that are likely to make the most difference toward eliminating the death and suffering caused by breast cancer. Published by the California Breast Cancer Research Program Special Research Initiatives.

Institute of Medicine report on Breast Cancer and the Environment: A Life Course Approach (2011) — Susan G. Komen for the Cure® provided funding for the Institute of Medicine (IOM) to review current evidence on breast cancer and the environment, consider gene–environment interactions, review the challenges in investigating environmental contributions to breast cancer, explore evidence-based actions that women might take to reduce their risk, and recommend research in all of these areas. The committee interpreted “environment” very broadly, to encompass all factors not directly inherited through DNA (e.g., how a woman grows and develops during her lifetime; what she eats and drinks; the physical, chemical, and microbial agents she encounters; how much physical activity she engages in; medical treatments and interventions she undergoes; and social and cultural practices that she experiences.)

International Agency for Research on Cancer (IARC) Medium-Term Strategy and Implementation Plan for 2010–2014 (2010) – Identifies how the IARC must orientate its activities over the next two decades such that it can best contribute to combating the projected increase in the global cancer burden.

National Institute of Environmental Health Sciences (NIEHS) Environmental Factors and Breast Cancer Risk – Briefly outlines the Institutes efforts to research the interplay of genetic, hormonal, and environment factors in increasing breast cancer risk, including the landmark Sister Study of 50,000 healthy sisters of women diagnosed with breast cancer, the impact of family history (e.g., the BRCA1 gene), cancer causing chemicals and exposures, research centers focusing on breast cancer and the environment, and the role of artificial light.

National Toxicology Program Report on Carcinogens (13th Edition, 2013) – U.S. Department of Health and Human Services Secretary Sylvia M. Burwell released the 13th Report on Carcinogens on October 2, 2014. The Report on Carcinogens (RoC) is a congressionally mandated, science-based, public health document that is prepared for the HHS Secretary by the National Toxicology Program. The report identifies agents, substances, mixtures, and exposure circumstances that are known or reasonably anticipated to cause cancer in humans.

Pathways to Breast Cancer: A Case Study for Innovation in Chemical Safety Evaluation (by Megan Schwarzman, MD, MPH and Sarah Janssen, MD, PhD, MPH, 2010) – Drawing on the fields of cancer biology, toxicology, medicine, epidemiology, public health, and public policy, a multidisciplinary expert panel reviewed existing methods for chemical toxicity testing and developed a testing scheme, called the Hazard Identification Approach. This approach provides a methodology for the identification of substances that could elevate breast cancer risk.


Reducing Environmental Cancer Risk, What We Can Do Now (2010) — The President’s Cancer Panel—a watchdog group of advisors charged with monitoring the National Cancer Program—released this report, which is the culmination of a series of hearings to gather input from experts and the public on the emerging evidence of links between environmental factors and cancer. The Panel was particularly concerned to find that the true burden of environmentally induced cancer has been grossly underestimated. With nearly 80,000 chemicals on the market in the U.S., many of which are used by millions of Americans in their daily lives and are un- or understudied and largely unregulated, exposure to potential environmental carcinogens is widespread.


State of the Evidence: The Connection Between Breast Cancer and the Environment (by Janet Gray, PhD, 2010) – The sixth edition of the Breast Cancer Fund’s signature report examining the scientific evidence linking exposures to environmental chemicals and radiation with breast cancer. In this edition, the evidence is placed in a larger conceptual context, with a substantial discussion of framing themes and methodological issues with new evidence cited in almost all categories of exposures covered.

The Falling Age of Puberty in U.S. Girls: What We Know, What We Need to Know (by Sandra Steingraber, PhD 2007) – This report is a review of the published literature on the timing of puberty in U.S. girls. It describes the basic biology of puberty, identifies the various determinants that seem to influence its onset and explores their possible interactions. Early puberty—in particular, early menarche—is a known risk factor for breast cancer. Ongoing ignorance about the extent to which chemical exposures are altering the timing of sexual maturation in children is directly attributable to a lack of basic data on the ability of common chemicals to act as endocrine disruptors.

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