The American Cancer Society reports that the median age when patients are diagnosed with breast cancer is 61. This means that half of all cases of breast cancer occur in people younger than 61, and half occur in people older than 61. Although breast cancer is considered a disease of aging, in some cases, exposure to certain compounds in the environment while we’re still developing in the womb could flip the switch that turns mutated cells into breast cancer later in life.

Dr. Ana Soto, professor of integrative physiology and pathobiology at Tufts University Medical School in Boston, has studied the effect of various so-called endocrine disruptors — chemicals that we’re exposed to throughout our lifetimes that may disrupt the hormonal balance in the body and create the right environment for cancer development. She says these chemicals include synthetic estrogens like estrogen diethylstilbestrol; DDT, a formerly widely-used insecticide; and bisphenol A, a component of many plastics.

[See: Breast Pain? Stop Worrying About Cancer.]

Breastcancer.org reports that “hormone disruptors can affect how estrogen and other hormones act in the body, by blocking them or mimicking them, which throws off the body’s hormonal balance.” This imbalance may lead to the development of cancer later in life, Soto says, because “chemicals that affect mammary gland development may also increase the propensity to develop breast cancer.”

Estrogen Diethylstilbestrol

The American Cancer Society reports that estrogen diethylstilbestrol was prescribed to pregnant women between 1938 and 1971, as it was believed to help prevent miscarriages and premature births. The ACS estimates that some five to 10 million people may have been exposed to the drug including mothers who were prescribed the drug and the children they were pregnant with while taking the drug. “Only those children who were in the womb at the time their mothers took DES were exposed to it. Brothers or sisters from pregnancies during which DES was not taken were not exposed,” the ACS reports.

Prescribing doctors didn’t know at the time that the drug was potentially dangerous, and the connection between cancer and DES only came to light when a group of seven girls in one town were all diagnosed with a very rare form of vaginal cancer in 1971. Soto says the drug was “given for the purpose of preventing miscarriages, although it was proven to be ineffective in this regard.” DES also increased the chances of babies born to DES mothers developing several types of cancer, including breast cancer, later in life.

When these women who’d been exposed to the estrogen diethylstilbestrol reached their 40s and started being screened for breast cancer, the incidence of breast cancer increased compared to controls who hadn’t been exposed, she says. “So we know [when the fetus is developing] is an area of vulnerability.”

Soto says other windows of vulnerability occur around puberty and around the time of menopause. “But I think that we can say practically, for different reasons, the mammary gland is sensitive to carcinogens throughout life. There are times that it’s more vulnerable to some insults,” such as when the fetus is developing and early childhood.

DDT

These windows of vulnerability also exist for other chemicals in the environment. The once ubiquitous insecticide DDT is another substance believed to cause breast cancer. The Environmental Protection Agency reports that DDT was so effective in reducing the population of mosquitoes (and reducing the transmission of malaria beginning in the 1940s) that it was sprayed widely across the United States until the USDA banned its use in 1972. A 2015 study in the Journal of Clinical Endocrinology & Metabolism suggested that exposure to DDT could quadruple a woman’s risk of developing breast cancer by age 52.

[See: 7 Innovations in Cancer Therapy.]

Bisphenol A

More recently, bisphenol A has garnered headlines for being a potentially dangerous substance that’s found in rigid plastics, aluminum can linings, heat-transfer cash register receipts and the environment. (As items that contain BPA degrade, they release their BPA molecules, which can then leach into groundwater and slip into the food chain from there.) Having a similar molecular structure to DES, BPA has been associated with a higher risk of developing breast cancer via a similar mechanism of interfering with hormone-related pathways in the body.

The Food and Drug Administration has been examining the evidence around BPA but has so far only banned its use in baby formula bottles. But some researchers, including Soto, believe the evidence warrants a change in current regulations. “When the fetal mammary gland is exposed to BPA in animals, these animals have an increased propensity to develop breast cancer during adulthood,” Soto says. Although the studies were done in animals, Soto believes that the findings are translatable to humans.

BPA was identified as being potentially dangerous within the past decade, and some companies replaced it with a substance called bisphenol S. However, in April 2017, a paper presented at ENDO 2017, the Endocrine Society’s annual meeting, also linked BPS to the later development of breast cancer.

Other Chemicals

The Susan G. Komen organization reports that polycyclic aromatic hydrocarbons , parbens, PCBs and dioxins — other chemicals found in everything from tobacco smoke and vehicle exhaust to cosmetics, adhesives, inks and diesel fuel — may also cause cancer. And there could be more chemicals we don’t even know about yet. The plastics industry got rolling in the early to mid-20 ^th century, and as babies born in the boom years of synthetic chemicals have aged, it may not be sheer coincidence that the rate of cancer development has also increased.

Soto says that the lifetime risk of a woman of her mother’s generation to contract breast cancer was one in 22, but this lifetime risk has increased to one in eight for her own generation. “I think we have plenty of evidence that the increased breast cancer incidence we have observed in the last 50 years cannot be explained by the genetic composition of the population. It’s too short a period for that. So we have to think that it’s due to environmental factors,” which include nutrition, exercise, time of menarche (when a girl’s period begins) and some of these chemicals, “because our mothers or grandmothers were neither exposed to these chemicals during fetal life, nor before age 50, while we have been.”

[See: A Tour of Mammographic Screenings During Your Life.]

Although there’s nothing that can be done about exposure you experienced in the past, you can try to reduce your exposure to endocrine disruptors in the future. Breastcancer.org recommends not microwaving any plastic products because the heat can break down some of the molecular bonds that hold the BPA, thereby causing it to be released into the food that’s being heated. Eating fewer canned foods, selecting products labeled “BPA-free” and using a glass, steel or ceramic water bottle rather than single-use plastic water bottles may also help you reduce your exposure to these chemicals.

Soto says it’s difficult to say for certain whether avoiding certain products will reduce your risk of breast cancer and if so, by how much, so in addition to avoiding exposure, she encourages people to contact their local and federal governments to take action against the continued use of endocrine disruptors. “Knock on the door of your representative in Congress,” she says. “We need laws” that prevent the use of these chemicals.

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Can Endocrine Disruptors Elevate Risk of Breast Cancer? originally appeared on usnews.com