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'Timing really matters' in link between DDT exposure, breast cancer risk
Women exposed to the insecticide p,p’-DDT appeared at increased risk for breast cancer through age 54 years, according to results of a prospective study published in Journal of the National Cancer Institute.
This risk depended on the timing of the first exposure. Women exposed before age 14 years — especially during infancy or early childhood — appeared more likely to develop premenopausal breast cancer, whereas women exposed after infancy had a higher risk for breast cancer between ages 50 and 54 years.
“What we have learned is that timing really matters. We know that if harmful exposures occur at times when breast tissue is rapidly changing, such as during puberty, they impact breast development in ways that can later result in cancer,” Barbara A. Cohn, PhD, director of child health and development studies at the Public Health Institute, said in a press release. “The research ... suggests that DDT affects breast cancer as an endocrine disruptor, that the period of time between first exposure and cancer risk seems to be around 40 years, and that other endocrine-disrupting chemicals could potentially simulate this kind of risk pattern.”
DDT was commonly used as a pesticide in the United States from the 1940s until 1972, when it was banned by the Environmental Protection Agency. Many other countries also banned DDT in the 1970s, although it is still used in some parts of Asia and Africa to fight malaria.
An earlier Child Health and Development Studies report showed associations between first exposure to DDT before puberty and a five times greater risk for breast cancer before age 50 years.
The current study expanded the observation window, analyzing 153 breast cancer cases diagnosed in women between ages 50 to 54 years. Researchers randomly assigned each case to up to three controls (n = 432), matched on birth year.
Serum samples collected during pregnancy (median age, 26 years) and 1 to 3 days after delivery between 1959 and 1967 underwent analysis for p,p’-DDT, o,p’-DDT, p,p’-DDE.
Results showed that for women of all ages at first DDT exposure, a doubling of serum p,p’-DDT appeared associated with a doubled risk for early postmenopausal breast cancer (OR = 1.99; 95% CI, 1.48-2.67).
Stratification revealed this association was driven by women first exposed after infancy (OR = 2.83; 95% CI, 1.96-4.10) vs. during infancy (OR = 0.56; 95% CI, 0.26-1.19).
For premenopausal breast cancer, p,p’-DDT was associated with increased risk among women who were first exposed from infancy to puberty, but not after (OR for first exposure during infancy = 3.7; 95% CI, 1.22-11.26).
“Even though there have been many studies of the environment and breast cancer, only a very small fraction have actually measured environmental exposures during windows of susceptibility, in this case early infancy and prior to menarche,” Mary Beth Terry, PhD, professor of epidemiology and environmental health sciences at the Mailman School of Public Health at Columbia University, said in the release. “The studies that have measured environmental exposures during windows of susceptibility, like our study, are much more consistent in supporting a positive association with breast cancer risk.” – by John DeRosier
Disclosures: This study was funded by the California Breast Cancer Research Program, NCI, National Institute of Environmental Health and Sciences, NIH and U.S. Department of Health and Human Services. The authors report no relevant financial disclosures.