Prenatal DDT Exposure Tied to Nearly Four-fold Increase in Breast Cancer Risk

Fifty-year study first to directly connect breast cancer risk to in utero chemical exposure

Oakland, CA (June 16, 2015) – Women who were exposed to higher levels of the pesticide DDT in utero—particularly a more estrogenic form, o,p’-DDT,  found in commercial DDT—were nearly four times more likely to be diagnosed with breast cancer as adults than women who were exposed to lower levels before birth, according to a new study published in the Endocrine Society’s Journal of Clinical Endocrinology & Metabolism (JCEM).

Despite being banned by many countries in the 1970s, DDT remains widespread in the environment and continues to be used to combat malaria in Africa and Asia. Many US women were exposed in utero in the 1960s, when the pesticide was used widely, and are now reaching the age of heightened breast cancer risk. 

“This 54-year study is the first to provide direct evidence that chemical exposures for pregnant women may have lifelong consequences for their daughters’ breast cancer risk,” said one of the study’s authors, Barbara A. Cohn, PhD, of the Public Health Institute (PHI) in Berkeley, CA. “Environmental chemicals have long been suspected causes of breast cancer, but until now, there have been few human studies to support this idea.”

DDT was among the first recognized endocrine disruptors. DDT and related pesticides can mimic and interfere with the function of the hormone estrogen. Past studies have found DDT exposure is linked to birth defects, reduced fertility and increased risk of Type 2 diabetes.

The researchers found that:

• Independent of the mother’s history of breast cancer, elevated levels of the more estrogenic form of DDT, o,p’-DDT, in the mother’s blood were associated with a nearly four-fold increase in the daughter’s risk of breast cancer. Among the women who were diagnosed with breast cancer, 83 percent had estrogen-receptor positive breast cancer, a form of cancer that may receive signals from the hormone estrogen to promote tumor growth.
• Exposure to higher levels of o,p’-DDT was associated with women being diagnosed with a more advanced stage of cancer.
• Women with greater exposure to o,p’-DDT were more likely to develop HER2-positive breast cancer, where the cancer cells have a gene mutation that produces an excess of a specific protein. Basic research studies where breast cancer cells were exposed to DDT have found the pesticide activated the HER2 protein.

Due to its effectiveness in killing mosquitoes, in 2006 the World Health Organization began promoting the use of DDT in an attempt to stem the tide of malaria deaths globally—a controversial decision that continues to be debated.

"This paper shows that the risks of using DDT are likely greater than previously known, while the benefits remain the same,” Cohn said. “Policy makers should take this into account."

The case-control study is prospective, having tracked the daughters of women who participated in PHI’s Child Health and Development Studies (CHDS) for 54 years, beginning in utero. CHDS studied 20,754 pregnancies among women who were members of the Kaiser Foundation Health Plan from 1959 to 1967. CHDS participants gave birth to 9,300 daughters during that period.

For the analysis published in JCEM, researchers used state records and a survey of CHDS participants’ grown daughters to determine how many were diagnosed with breast cancer by age 52. To determine levels of DDT exposure in the womb, the researchers analyzed stored blood samples to measure DDT levels in the mothers’ blood during pregnancy or in the days immediately after delivery. They examined the mothers of 118 women who were diagnosed with breast cancer and also identified 354 daughters who did not develop cancer and tested their mothers’ blood for comparison.

“This study calls for a new emphasis on finding and controlling environmental causes of breast cancer that operate in the womb,” Cohn said. “Our findings should prompt additional clinical and laboratory studies that can lead to prevention, early detection and treatment of DDT-associated breast cancer in the many generations of women who were exposed in the womb. We also are continuing to research other chemicals to see which may impact breast cancer risk among our study participants.”

Other authors of the study include: Michele La Merrill of the University of California, Davis, in Davis, CA; Nickilou Y. Krigbaum, Lauren Zimmermann and Piera M. Cirillo of the Public Health Institute in Berkeley, CA; and Gregory Yeh and June-Soo Park of the California Department of Toxic Substances Control in Berkeley, CA.

The research was supported with funding from the California Breast Cancer Research Program, the Eunice Kennedy Shriver National Institute of Child Health and Development, The National Institute of Environmental Heatlh Sciences, the California Public Health Department, the National Cancer Institute’s Surveillance, Epidemiology and End Results Program, and the U.S. Centers for Disease Control and Prevention’s National Program of Cancer Registries.

The study, “DDT Exposure in Utero and Breast Cancer,” is available online.

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For more information, contact Jennifer Scroggins at jennifer.scroggins@phi.org or 510-285-5512.

About the Child Health and Development Studies
The Child Health and Development Studies (CHDS) is a project of the Public Health Institute. CHDS is committed to investigating how health and disease are passed on between generations—not just by genes, but also through social, personal, and environmental surroundings.
 
About the Public Health Institute 
The Public Health Institute, an independent nonprofit organization, is dedicated to promoting health, well-being and quality of life for people throughout California, across the nation and around the world.