Breast cancer and the environment

Breast cancer's toll

Too many women are diagnosed with breast cancer each year in the United States. A woman born in the U.S. today has a one in eight chance of developing invasive breast cancer during her lifetime. It is now the most commonly diagnosed cancer in the country and in the world, surpassing lung cancer. While fewer women are dying from the disease thanks to advances in early detection and treatment, the number of new cases remains stubbornly high and continues to rise.

The rise in early-onset breast cancer is especially concerning. Rates are climbing fastest among young women—often just as they’re launching their careers and starting families. This trend affects nearly all racial and ethnic groups, with Black women experiencing higher rates than White women. Cases of early onset disease are also rising in Asian-American, Indigenous, and Hispanic women.

Adding to the burden is the enormous cost of the disease. According to the National Cancer Institute, breast cancer is the most expensive cancer. Medical costs associated with the disease reached $29.8 billion in 2020. With the rising cost of new treatments and ever-escalating out-of-pocket expenses, more and more patients are going into debt, reflecting a system of cancer care that is financially unsustainable.

Multiple risk factors

There are many factors that influence a woman’s chances of developing breast cancer. Exposure to radiation, consuming alcohol, postmenopausal weight gain, and not being physically active are well-known risk factors. Women with certain inherited genetic mutations or a strong family history of the disease also have an increased risk.

Another important risk factor is prolonged exposure to estrogen and other hormones that play a role at various stages in a woman’s life. For instance, early menarche (first period), late menopause, delayed childbearing, and not breastfeeding can increase a woman’s lifelong exposure to estrogen and, as a result, her risk of developing breast cancer.

So, what else might explain the high incidence rates? Mounting evidence—especially for early-onset disease—points to hazardous chemicals in our everyday environment as important and often overlooked contributing factors. These are chemicals we are exposed to through the air we breathe, the food we eat, the water we drink, and the products we use. Many of them have been linked with breast cancer.

The role of environmental chemicals

In the aftermath of World War II, industry began producing large quantities of synthetic chemicals—including pesticides, plastics, solvents, and other substances—with little regard for safety. These chemicals made their way into our everyday products and into our environment. Since then, tens of thousands of chemicals have been produced and sold on the market, the vast majority of which have not been tested for their effects on human health. Even when testing is done by regulatory agencies, current methods do not adequately consider the effects of chemicals on the breast.

Over the last couple of decades, studies have shown that chemicals can trigger breast cancer in many different ways. They can damage DNA, causing a cancerous tumor to form; they can make breast cells grow uncontrollably; and they can change the way the breast develops, leaving it more vulnerable to carcinogens.

Using products isn’t the only way people can be exposed to chemicals. EDCs, for example, can migrate out of items like furniture, build up in indoor air and dust, and enter our bodies. In a study in 2003, Silent Spring scientists detected dozens of EDCs in air and dust inside the home, showing for the first time that everyday consumer products are a major source of indoor air pollution. We also made the first measurements of EDCs in drinking water supplies on Cape Cod—highlighting drinking water is another important route of exposure.

Today, Silent Spring continues to develop innovative screening methods to predict which chemicals may increase breast cancer risk. Our researchers are also studying the human exposome—the full range of environmental exposures over a person’s lifetime—in women firefighters and nurses, uncovering new exposures tied to biological markers associated with early signs of breast cancer.

This work is helping to identify hidden sources of hazardous chemicals in our daily lives and reveal new opportunities to prevent breast cancer and other diseases.

Exposures early in life matter

Studies suggest the origins of breast cancer may occur early in life—in the womb, during puberty, and through pregnancy. These critical time periods are commonly referred to as “windows of susceptibility,” developmental stages when an individual may be most vulnerable to environmental exposures.

In a comprehensive review of epidemiology studies, Silent Spring scientists uncovered strong evidence linking early exposures with an increased risk of breast cancer later in life. Early exposures to DDT, dioxins, PFOSA (a type of PFAS), and air pollution, were found to be associated with a two- to five-fold increased risk of breast cancer. Similarly, early exposure in the workplace to high levels of organic solvents and gasoline components was another important risk factor.

One of the clearest examples of the lifelong consequences of early life exposures can be seen in the Child Health and Development Studies (CHDS). In this unique and valuable multigenerational study, researchers collected blood samples from women in the 1950s and ‘60s and followed the women and their children to see who developed breast cancer.

The study found that women who were exposed to high levels of DDT before the age of 14, when the pesticide came into widespread use, had a five-fold increased risk of developing breast cancer by age 50. What’s more, when the researchers looked at the daughters, those whose mothers had higher blood levels of DDT during pregnancy had a four-fold increased risk of developing breast cancer later on. 

Prevention is possible

Unlike other factors such as genetic susceptibility, environmental chemicals are modifiable risk factors—things we can change. If we can reduce people’s exposures to hazardous chemicals, we can prevent disease.

Consider the Women’s Health Initiative study, which found that postmenopausal women taking combination hormone replacement therapy (HRT) had an increased risk of developing breast cancer, heart disease, stroke, blood clots, and other effects. Because the risks of taking HRT were found to outweigh the benefits, women stopped taking the drugs starting in 2002. As a result, approximately 12,600 women a year in the United States were spared a breast cancer diagnosis. Imagine how many more women could be spared a diagnosis by removing hormone-disrupting chemicals from our environment.

Starting with the publication of the President’s Cancer Panel report on environmental pollutants and cancer, followed by the Institute of Medicine’s report on breast cancer and the environment, we have begun to see a shift in the way the nation’s physicians and scientists think about how to prevent breast cancer. Rather than waiting for definitive proof that certain chemicals cause human harm before acting, many experts are calling for a new emphasis on cancer prevention that is focused on reducing people’s exposures to toxic chemicals.