Articles & Resources

State of Evidence: Breast Cancer and the Environment

By Nancy Evans, Health Science Consultant, Breast Cancer Fund

As organizations and individuals concerned with breast cancer and other environmentally mediated illnesses, we are aware of the many ways in which science demonstrates that human health and the environment are intimately linked. We also recognize that public health measures have long been, and will likely continue to be, our best hope to reduce the incidence of breast cancer, other cancers, and many other chronic diseases of our time.

The breast cancer epidemic continues. In 2005, breast cancer struck an estimated 211,000 women in the U.S.[1] and more than 1.1 million worldwide - more than any other type of cancer except skin cancer [2]. While environmental factors do not solely account for the increasing incidence of the disease since 1950, neither known risk factors nor improved diagnostic methods explain the escalation in incidence of breast cancer.

Animal and cell studies clearly identify dozens of chemicals that cause mammary tumors or mimic the activity of estrogen, a known breast cancer risk factor, and research evidence documents widespread human exposure. This evidence provides a compelling basis for reducing exposures while we continue to investigate links between the environment and breast cancer.

According to the National Cancer Institute, more than 100,000 chemicals are in use today in the United States [3]. Less than 10 percent of these chemicals have been tested for their effects on human health. As long as 90% of the chemicals we are exposed to are untested for their impact on human health, any public health statement that seeks to minimize the contributing role of chemicals to breast cancer or other diseases should recognize the limited evidentiary base on which it is made.

Exposure to ionizing radiation is the longest-established environmental cause of human breast cancer in both women and men. In 2005, the National Toxicology Program classified X-radiation and gamma radiation as known human carcinogens, because "exposure to these kinds of radiation causes many types of cancer including leukemia and cancers of the thyroid, breast and lung [4]." Also in 2005, a report from the National Research Council established that there is no safe dose of radiation, that "the smallest dose has the potential to cause a small increase in risk [of cancer] to humans [5]." Ionizing radiation is a mutagen as well as a carcinogen, and may even enhance the ability of hormones or other chemicals to cause cancer [6].

An epidemic of cancer and chronic disease
Breast cancer is part of a larger cancer epidemic: the lifetime risk of some type of cancer in the U.S. is 1 in 3 for women and 1 in 2 for men [7]. Once rare, cancer is now a familiar occurrence in our population and evidence linking cancer and environmental exposures continues to mount.

Concerns extend beyond breast cancer, and indeed beyond cancer in general, to the extraordinary number of chronic diseases in the United States and how many of those diseases may be linked to environmental exposures. An estimated 125 million Americans, or 43 percent of the population, have at least one chronic illness, while 60 million people, or 21 percent of the population, suffer from multiple chronic conditions. Nearly 20 million American children suffer from at least one chronic health problem [8]. Cancer, asthma, heart disease, birth defects, developmental disabilities, diabetes, endometriosis, infertility, and Parkinson's disease are among the chronic conditions becoming increasingly common. Scientific understanding of the role of environmental factors varies across this spectrum of diseases, but the emerging evidence is powerful and frequently includes chemical contaminants as contributing to the growing toll of human suffering.

Common threads in a complex puzzle
Although links between exposures to environmental contaminants and health effects have been known for centuries, emerging science gives us new insights into the changing patterns and mechanisms of disease and disability. For example, most cancers cannot be attributed to a single cause but rather to an incredibly complex interplay of genetic and environmental factors over time, beginning with fetal development. Repeated environmental insults or "hits" throughout life can alter gene expression, damage the immune system, and alter cellular function, including disruption of cell signaling, thereby putting a person on the pathway to cancer or autism or Parkinson's or one of a host of diseases and disorders later in life. Within the complexities of each of these diseases, common elements can be seen. Some of the same environmental exposures are linked to different diseases, depending on the age and genetic makeup of an individual at the time of exposure. For example, fetal exposure to certain polychlorinated biphenyls (PCBs) may cause neurodevelopmental effects in some individuals and contribute to breast cancer risk in others. Finding ways to prevent these diseases requires a new paradigm for solutions based on an interdisciplinary and precautionary approach. Only through collaboration among scientists, health-affected communities, policy makers and the public will we find meaningful solutions to protect human health and the health of the planet.

Measuring the pollution in people
When most people hear the word "pollution," they think of chemicals that have contaminated the external environment - their neighborhood, their town, their air or water. But research by the Centers for Disease Control and Prevention (CDC) shows that pollution is personal - the external environment has invaded our internal environment. CDC scientists have found measurable levels of 148 chemicals in the blood and urine of Americans of all ages [9]. Biomonitoring, the process of measuring our chemical body burden, reveals widespread exposure to complex mixtures of toxic chemicals.

Timing of exposure matters
More than two decades of research on laboratory animals, wildlife and cell behavior demonstrate the inadequacy of the old adage, "the dose makes the poison." Today's scientists know that the timing, duration, and pattern of exposure are equally if not more important than the dose. Low dose exposure to environmental chemicals - parts per billion or even per trillion - during a critical window of development can cause profound, irreversible effects on organs and systems.

The tragic legacy of diethylstilbestrol (DES), a drug prescribed between 1941 to 1971 to prevent miscarriages, shows that cancer can begin in the womb [10]. Women's bodies are the first environments for the next generation, but sadly, it is now clear that toxic chemicals reach even this once-believed safe place. CDC scientists found that women have higher levels of some chemicals in their bodies than men do. A recent study of umbilical cord blood of newborn infants revealed the presence of an average of 200 industrial chemicals per cord blood sample [11].

Multiple and chronic exposures
Each of us is exposed to hundreds of synthetic chemicals every day--at home, at school, at work, and as we travel from place to place. However, much of what we know about the health effects of exposure to synthetic chemicals comes from occupational health research. Workers are exposed on a daily basis to higher levels of chemicals than the general public. Aircraft and automotive workers, barbers and hairdressers, chemists, farmers, paper mill workers, and microelectronics workers and women in many other jobs are exposed to known mammary carcinogens [12, 13]. Chemicals used in these occupations ultimately enter the larger environment when they are carried home on work clothes, added to consumer products, dumped into landfills or released into the air or water [14]. Workers and communities near industrial sites are at greatest risk of harm. We must ensure that no population bears an adverse burden of chemical exposures.

We need precautionary measures to protect human health
Research on environmental contributors to breast cancer and other diseases should be aggressively expanded. But while research continues, scientific uncertainty should not be a reason for inaction on public health policy. Breast cancer is a symptom of a larger public health crisis that demands action by society as a whole.

For more information, register for "What is the Connection Between the Environment and Breast Cancer", a lecture given by Silent Spring Institute, a nationally recognized leader in research on breast cancer and the environment, on Wednesday, January 10 from 7:30 - 9 p.m. at the New Canaan Nature Center. Call (203) 966-9577 to register.

References:
1. American Cancer Society (2005). Cancer Facts and Figures, 2005.
2. Parkin DM, Bray F, Ferlay J, Pisani P (2005). Global cancer statistics, 2002. CA: A Cancer Journal for Clinicians 55:74-108.
3. National Cancer Institute (2003). Cancer and the environment: What you need to know, what you can do. National Institutes of Health.
4. National Toxicology Program (2005). Eleventh Report on Carcinogens. National Institute of Environmental Health Sciences. National Institutes of Health.
5. National Research Council (2005). Biologic effects of ionizing radiation VII: Health risks from exposure to low levels of ionizing radiation. National Academy of Science, Washington DC.
6. Calaf GM, Hei TK (2000). Establishment of a radiation and estrogen-induced breast cancer model. Carcinogenesis 21:769-776.
7. Jemal A, Murray T, Ward E, Samuels A, et al (2005). Cancer Statistics, 2005. CA: A Cancer Journal for Clinicians. 55:10-30.
8. Partnership for Solutions: Better Lives for People with Chronic Conditions (2003). http://www.nccconline.org/pdf/PrevalenceandCostFacts.pdf
9. CDC (2005). Third National Report on Human Exposure to Environmental Chemicals. Atlanta: Centers for Disease Control and Prevention.
10. Herbst All, Scully RE (1970). Adenocarcinoma of the vagina in adolescence. A report of seven cases including six clear cell carcinomas (so-called mesonephromas). Cancer 25:745-757.
11. Environmental Working Group (2005). Body Burden 2: The Pollution in Newborns. http://ewg.reports/bodyburden2.
12. Brody JG, Rudel RA. (2003). Environmental pollutants and breast cancer. Environmental Health Perspectives 111(8):1007-1019.
13. Breast Cancer Fund and Breast Cancer Action (2006). State of the Evidence: What is the Connection Between the Environment and Breast Cancer?. 4th edition., p. 46
14. Steingraber S (1997). Living downstream: An ecologist looks at cancer and the environment. Reading M A: Addison-Wesley, p. 64.