A new research has established that women who were exposed to higher levels of the pesticide DDT in utero were at four times greater risk of being diagnosed with breast cancer in their adulthood than women who were exposed to lower levels before birth.
Published in the Endocrine Society’s Journal of Clinical Endocrinology and Metabolism (JCEM), the research found that a more estrogenic form of DDT, o,p’-DDT, was largely responsible for this finding.
DDT has already been banned in many countries, but there are still parts of the world – Asia and Africa – where the pesticide is being used exposing lots and lots of people of potential risks. The pesticide was among the first recognized endocrine disruptors, according to the introductory guide to endocrine-disrupting chemicals published by the Endocrine Society and IPEN.
The reason for this classification is that DDT and related pesticides can mimic and interfere with the function of the hormone estrogen and previous studies have already linked DDT exposure to birth defects, reduced fertility and increased risk of Type 2 diabetes.
The latest study is a prospective one which tracked the daughters of women who participated in the 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 from1959 through 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 utero, the researchers analyzed stored blood samples from CHDS to measure DDT levels in the mothers’ blood during pregnancy or in the days immediately after delivery. The researchers measured DDT levels in mothers of 118 women who were diagnosed with breast cancer. The scientists identified 354 daughters who did not develop cancer to use as controls and tested their mothers’ blood for comparison.
“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 in Berkeley, Calif. “Environmental chemicals have long been suspected causes of breast cancer, but until now, there have been few human studies to support this idea.”
The researchers found that independent of the mother’s history of breast cancer, elevated levels of 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.
Researchers also determined that exposure to higher levels of o,p’-DDT was associated with women being diagnosed with a more advanced stage of cancer. In addition, the scientists found 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.
‘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.’
