The Environment and Breast Cancer: What’s the Connection?

By Sarah Dunagan

Breast cancer is the leading type of cancer in women in the United States, and the leading cause of death in women between their late thirties and early fifties.* Breast cancer incidence rates continue to rise worldwide, with the highest risk in industrialized western countries.

Studies that show increased risk for women who move from low-incidence regions to high-incidence countries, like the United States, point to something about the way we live in industrial societies.
“It was overwhelming to know how many chemicals they found in my house…I’ve made really conscious efforts to eliminate so many things — my lawn, everything on the food that I eat… I’ve made so many…changes…and to know that even so many years after my diagnosis, to know that I’m still being exposed. It’s overwhelming.”
–participant in the Silent Spring Institute’s Household Exposure Study
It is estimated that only 10% of women who develop breast cancer have a high-risk inherited gene that increases their susceptibility. Identifying additional non-inherited factors is critical, because it will tell us ways to reduce risk.
Although the exact mechanisms are not fully understood, laboratory research shows that chemicals may contribute to breast cancer risk by damaging DNA, promoting tumor growth, or increasing susceptibility by altering how mammary glands develop.
Testing chemicals in animals is currently the primary way of identifying chemicals that might cause cancer in humans. To date, studies on animals have found 216 chemicals that cause mammary gland tumors. Exposure to these chemicals is widespread since they are commonly found in people’s bodies and in the environment, including homes.
Sources of mammary carcinogens include
  • vehicle exhaust
  • air pollution
  • tobacco smoke
  • pesticides
  • pharmaceuticals

“I never thought about buying a car as anything to do with breast cancer. Knowing that the auto exhaust contains mammary carcinogens puts fuel efficiency in a whole new light. ”
~breast cancer activist

Most of the chemicals people are exposed to have never been tested for cancer risk, so improved and expanding testing of chemicals is essential.

Many of the established risk factors for breast cancer – such as a woman’s reproductive history and hormone replacement therapy use – are related to a woman’s lifetime exposure to estrogen; so it is important to investigate the effects of chemicals in the environment that may behave like estrogen.
Cell studies have identified a group of chemicals, known as endocrine disrupting compounds (EDCs), which can mimic or block hormones, and are thought to affect breast cancer risk.
EDCs are found in
  • some plastics
  • pesticides
  • detergents
  • and cosmetics, among other sources.
Recent studies on humans have strengthened the evidence that environmental pollutants affect breast cancer risk.
Studies have shown that women with both high exposure to PCBs (polychlorinated byphenols – banned chemicals previously used in electrical equipment and other products) and a genetic variation that affects how their bodies process chemicals have about three times higher breast cancer risk than women who don’t have this combination of factors.
Several recent studies also found that breast cancer risk increases with exposure to polycyclic aromatic hydrocarbons (PAHs), which are in:
  • air pollution from vehicle exhaust and combustion
  • tobacco smoke
  • and grilled or smoked food.
A recent study found a link between young girls’ exposure to DDT – a banned pesticide – and development of breast cancer later in life. This highlights increased vulnerability to the effects of these chemicals when exposure occurs early in life.
While researchers continue to investigate the connections between the environment and breast cancer, we have enough evidence to take precautionary steps now to protect our health by reducing exposures to potentially harmful chemicals.For more information about links between chemicals and breast cancer, visit the Environment and Breast Cancer: Science Review database on the Silent Spring Institute website.

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