Breast Cancer and the Environment

A 2011 report from the Institute of Medicine (IOM)Breast Cancer and the Environment: A Life Course Approach, examines the existing literature on breast cancer risk posed by various environmental factors, highlights actions that offer potential to reduce risk, and recommends key areas for future research. The report, sponsored by Susan G. Komen for the Cure, was released on December 7th with a press release and report briefing. The findings were then presented formally in a plenary session at the 2011 San Antonio Breast Cancer Symposium.

According to the IOM report summary:

“Women may have some opportunities to reduce their risk of breast cancer through personal actions, such as avoiding unnecessary medical radiation throughout life, avoiding the 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.”

In other words, the report told us what we already know.

There are a few known risk factors that account for a relatively small percentage of breast cancer cases. It’s hard to study environmental causation; more research is needed across the lifespan. And, we need better methods to test agents that may be contributing to breast cancer and to explore the effects of combined exposures.

In addition to restating these existing conclusions, the report may have done more to mystify than to clarify. Genetics alone cannot explain the rise in breast cancer incidence in the United States. 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, and notably, the longer immigrant women live in the U.S. the more likely they are to get breast cancer.

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

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 piece of a complex puzzle that alters breast cancer risk. 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 nation, 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, which was founded in 1993, also argue that the rise in breast cancer incidence is not surprising given a number of synthetic chemicals that entered the marketplace after World War II. Many of these chemicals contain 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 (now in its 6th edition), 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. Incidentally, the NIEHS links to the Breast Cancer Fund’s State of the Evidence report on its website as a key resource.

Indeed, 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, however, is that the environment matters.

Although the IOM report authoritatively confirms that existing concern about environmental links is valid, it is concerning in other ways.

First, the report focuses on a definition of the environment that is much too broad (i.e., all factors that are not directly inherited through DNA, p. 1-4) with a strong emphasis on lifestyle factors as environmental. Second, it downplays the dangers of industrial chemicals (i.e., those that are biologically plausible but not causally confirmed in humans, p. 3-4) and fails to stress precautionary principles when dealing with toxic substances implicated in the development of breast cancer (e.g., endocrine disruptors, p. 3-36). Third, the report puts too much emphasis on the weighty but contradictory message that women should “take action” to reduce their breast cancer risk even though, “based on the existing literature…it [is] difficult to estimate the magnitude of the potential impact of these actions on either individuals or population groups.” (p. 6-19).

The report is also confusing when it comes to the future of environmental cancer research.

For example, the report identifies key areas of study, such as circadian rhythm, endocrine activity and interactions between chemicals (e.g., BPA and other suspect culprits), the degree to which chemicals known to mutate genes (such as polycyclic aromatic hydrocarbons, benzene, and ethylene oxide) contribute to breast cancer risk, and the potential importance of environmental chemicals (such as BPA) that change how genes function.

Studies are already underway in these areas and yes, more are needed. Yet, the report simultaneously emphasizes seemingly insurmountable barriers to such research.

“Tracing multiple and potentially interacting causes of breast cancer will be difficult. Some risk factors may have very weak effects or effects in only a small portion of the population, making their contribution to risk hard to detect. People are exposed to a complex and changing mix of environmental agents over the course of a lifetime; discerning the effects of an individual agent, or knowing whether the components of the mixture may interact to influence the development of disease, is not straightforward. Moreover, many of these agents have never been studied in ways that could indicate whether they might be relevant to breast cancer. Several challenges appear especially formidable.” (IOM Summary, p. S-5)

The iterative practice of scientific research is at work no doubt. But for the public, it looks like we’re back to square one. Risk reduction is a personal responsibility. Don’t smoke, exercise, eat right, avoid too much alcohol, try not to disrupt your hormones, don’t have too many x-rays. Fine advice. But far too many people have done all of these things and still got breast cancer.

Breast cancer activists criticized the report for the same reasons.

Jeannie Rizzo of The Breast Cancer Fund told Forbes that, “The failure to take a precautionary approach may leave the public confused and even misinformed, as is evidenced by some of the initial media headlines about the report that say that chemicals are unproven to raise breast cancer risk, when the report itself indicated there are plausible reasons for concern.”

Similarly, Karuna Jaggar of Breast Cancer Action told USA Today that, “Waiting for absolute proof is killing us. We need to take steps now to prevent women from being exposed to chemicals that increase their risk of breast cancer.”

I agree. If women are routinely charged with the responsibility of knowing their risk and taking proactive steps to reduce it, perhaps society should be held to the same standard. The evidence linking cancer and the environment is plentiful.


Additional Resources (alphabetical listing):

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 program 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, Ph.D., 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.

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.

State of the Evidence: The Connection Between Breast Cancer and the Environment (by Janet Gray, Ph.D., 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, Ph.D. 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.


For more analysis of the IOM report, see Breast Cancer Action Briefing for Advocates (Webinar) – Breast Cancer Action’s executive director, Karuna Jaggar was joined by Janet Ackerman, Research Assistant at the Silent Spring Institute on Jan 24th and joined by Ruthann Rudel, MS, Director of Research at the Silent Spring Institute on Jan 25th. The webinar provided: BCAction’s commentary and analysis of the IOM report on breast cancer and the environment; A summary of where the report got it right and where it missed the mark; A focus on the limits of individual behavior and the policy changes required to reduce these exposures to toxins that may be contributing to the skyrocketing rates of breast and other cancers; A review of the committee’s recommendations and information on how advocates can move the recommendations forward.


 

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