What Is the Connection Between the Environment and Breast Cancer?
Edited by Nancy Evans, Health Science Consultant, Breast Cancer Fund

Breast cancer rates have been climbing steadily in the United States and other industrialized countries since the 1940s, amounting to more than one million cases per year worldwide. In 2004, in the United States alone, an estimated 215,990 women will be diagnosed with invasive breast cancer and more than 55,390 women will be diagnosed with in situ breast cancer, meaning the tumor is confined to its original location in the breast. This year, breast cancer is expected to kill more than 40,000 American women and more than 370,000 women worldwide. Billions of dollars have been spent in an effort to stem this unrelenting tide, yet as many as half of all breast cancers occur in women who have no known risk factors for the disease. Less than one out of every 10 cases occurs in women born with genetic predisposition for the disease.

Research indicates that breast cancer arises for four primary reasons: genetic mutation, altered gene expression, altered cell interaction or from exposure to agents that alter the body’s natural production of estrogen and other hormones. Not everyone exposed to a carcinogen will develop breast cancer, however. In fact, the development of breast cancer and other cancers is a multi-step process that most commonly results from more than one exposure over time. For example, one exposure might occur prenatally, another during childhood and a third during adolescence. Each of these exposures increase the risk of breast cancer in later life. Depending on the individual, cancer might develop after just two exposures, perhaps after dozens more, or may not develop at all.

Ionizing radiation is the best-established environmental cause of human breast cancer. A growing body of evidence also implicates non-ionizing radiation (electromagnetic fields and radio-frequency radiation) as a possible contributor to the development of breast cancer. In addition, compelling scientific evidence points to some of the 85,000 synthetic chemicals in use today as contributing to the development of breast cancer, either by altering hormone function or gene expression. As with ionizing radiation, some synthetic chemicals (called mutagens) also can cause gene mutations that lead to breast cancer. While there is no simple method for linking chemical exposures to breast cancer, several types of research—experimental, body burden and epidemiological studies—yield evidence that such a link exists.

For women born without genetic predisposition for breast cancer, events during their lifetimes contribute to producing the disease. But genetic predisposition does not cause breast cancer. Rather, it means that women with inherited predisposition are more sensitive to the effects of breast carcinogens than those without a genetic predisposition.

There is broad agreement that exposure over time to estrogens that are naturally produced in the body increases the risk of breast cancer. Thus, the earlier in life a woman’s menstrual cycle begins and the later it ends, the higher her risk of breast cancer. Hormones administered as pharmaceuticals also increase this risk. The Women’s Health Initiative study on Hormone Replacement Therapy (HRT) was halted when it became clear that women who regularly took HRT had significantly higher rates of breast cancer (as well as other potentially life-threatening diseases). The National Toxicology Program now lists steroidal estrogens as known human carcinogens.1 Since 1987, the International Agency for Research on Cancer (IARC) has categorized nonsteroidal estrogens as known human carcinogens. Other compounds with estrogenic activity, including drugs such as diethylstilbestrol (DES) and pesticides such as dieldrin, are understood to increase the risk of breast cancer. In addition, plastic additives such as bisphenol-A (BPA), polyvinyl chloride (PVC, which is found in many consumer products) and gasoline additives such as benzene, solvents and degreasing agents may be linked with increased risk of breast cancer due to their estrogenic activity.

Experimental studies have identified a number of synthetic chemicals that induce mammary cancer in rodents. These include: organic solvents (used in many manufacturing processes, including the manufacture of computer components); polycyclic aromatic hydrocarbons (PAHs, produced from combustion of gasoline, diesel, heating oil, cigarettes and other tobacco products, or by grilling meats and fish at high temperature); and 1,3-butadiene, which is both an air pollutant created by internal combustion engines and petroleum refineries, as well as a chemical used in the manufacture and processing of synthetic rubber products and some fungicides.

There also is experimental evidence that certain chemicals can disrupt hormone function and thereby may increase the risk of breast cancer. These chemicals include the insecticide heptachlor, the herbicide atrazine and ingredients in some sunscreens. Others include certain phthalates, which are compounds used to make plastic soft and flexible, and parabens, which are chemicals that act as preservatives. Both phthalates and parabens are widely used ingredients in personal care products.

Body burden studies measure the presence of chemicals in people by analyzing blood, urine, body fat or breast milk. Also called biomonitoring, this type of research is used to study possible connections between chemicals and breast cancer. These studies cannot establish cause but can reveal the internal contamination of women’s bodies. Studies by the Centers for Disease Control and Prevention (CDC) show that Americans of all ages carry a body burden of at least 116 chemicals, some of them banned for more than two decades because of toxicity.²

Public health studies that have followed the development of breast cancer in women over time have identified a number of other compounds as likely contributors to the development of the disease, although the evidence remains incon-sistent. These chemicals include: dioxin, created when chlorinated materials such as plastics are burned; the pesticide DDT (dichloro-diphenyltrichloroethane) and its metabolite and environmental breakdown product DDE; and some forms of PCBs (polychlorinated biphenyls), once widely used in the manufacture of electrical equipment, carbonless paper and other industrial and consumer products.

We clearly have major gaps in our current knowledge about the links between breast cancer and the environment. Research efforts should be focused, therefore, in areas most likely to provide useful information for shaping public policies around environmental exposures and public health. The types of research most likely to produce useful evidence will be those examining:

(1) the interplay between the timing of exposures (especially periods of vulnerability), multiple exposures and chronic exposures (including occupational exposures and secondhand smoke);

(2)disparities in health outcomes and differences in exposures among racial groups;

(3) human contamination, measured by biomonitoring; and

(4)public health studies examining unexplained patterns of breast cancer.

 

To reduce the burden of breast cancer in our society, public officials and the scientific and corporate communities must act based on what is already known about agents that increase the risk of breast cancer. More research on avoidable causes of the disease is also required. Studies that ask tough and honest questions about the underlying causes of breast cancer, including research based on recommendations from the first International Summit on Breast Cancer and the Environment, must be pursued. This 2002 summit was sponsored by the CDC. While this research proceeds, fundamental changes are needed in both the public and private sectors regarding the production, use and disposal of chemicals found to increase the risk of breast cancer, specifically controlling or removing many of these substances from the environment and reducing exposure to both ionizing and non-ionizing radiation.

Considerable resources are spent encouraging women to make changes in their personal lives that might reduce their risk of breast cancer. But many factors that contribute to the disease lie far beyond an individual’s personal control and can only be addressed by government policy and private sector changes. Breast cancer is not just a personal tragedy; it is a public health crisis that requires political will to change the status quo.

This crisis must be addressed by implementing the precautionary principle as a matter of public policy. Under this principle, evidence of harm, rather than definitive proof of harm, becomes the trigger for policy action. In addition, the precautionary principle mandates that proponents of chemicals and radiological products and processes assess their health, safety and environmental impacts before introducing them to the marketplace, and make that information publicly available. The burden to provide such information thus lies with manufacturers and sellers, not with the public. An obligation exists for manufacturers to examine a full range of alternatives to toxic ingredients and to select the alternative with the least potential impact on human health and the environment, including the alternative of not bringing questionable products to the market at all. The precautionary principle rests on the democratic principle that government officials are obligated to serve the public interest by protecting human health and the environment. Decisions applying the precautionary principle must be transparent, participatory and informed by the best available information.

Six-point Plan to Help Reduce the Risk of Breast Cancer and Ultimately End the Epidemic

1. Phase out chemicals known to cause cancer or genetic harm. Test all other chemicals currently in use and proposed for market to determine the effects on human health and the environment. Make this information available to the public.

2.  Educate the public about the health effects of radiation and on how to reduce exposure to both ionizing and non-ionizing radiation.

3. Monitor the chemical body burden and resultant health outcomes in humans using biospecimens (blood, urine, fat and breast milk). Establish a comprehensive community program to detect synthetic chemicals and their metabolic products in people, document any geographic distribution patterns and health outcomes, and initiate a plan to eliminate these contaminants.

4. Hold corporations accountable for hazardous practices and offer incentives for clean, green practices.

5.  Enact “sunshine” laws and enforce existing environmental protection laws.

6. Practice “healthy purchasing,” with local, state and federal governments leading the way in purchasing environmentally preferable products, so as to create an example for corporations and individuals to follow.

Implementing this plan depends on collaboration Increasing evidence that chemicals and radiation and cooperation among individuals and are contributing to the rising tide of breast cancer organizations with varying agendas. There must not be ignored. Government and the private are well-established networks of experienced sector have an obligation to act on this evidence by environmental and health organizations that can supporting and implementing public policies that act as resources to move this effort forward. put health first. Now is the time to change the dangerous course we are on.

 

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