timing of DDT exposure important in whether it raises risk of breast cancer

[Lani]

New Evidence Links Breast Cancer to Pesticide DDT [Public Health Institute]
OAKLAND, CA — At a time when the pesticide DDT is once again being promoted to combat malaria, researchers have found new evidence linking DDT to breast cancer, according to a study to be published in the scientific journal "Environmental Health Perspectives."
Entitled "DDT and Breast Cancer in Young Women: New Data on the Significance of Age at Exposure," the study will be printed in October's edition of this peer-reviewed journal. An electronic copy is already available online.
High levels of p,p'- DDT, the primary component of DDT, in women exposed before mid-adolescence, were found to be predict a five-fold increase in breast cancer risk. Many American women heavily exposed to DDT in childhood have not yet reached 50 years of age, therefore the public health significance of DDT exposure in early life may be large. This is the first study to examine how exposure in early life affects later life risk for breast cancer.
Based on these findings, researchers from the California-based Public Health Institute and Mount Sinai School of Medicine in New York conclude that it is too soon to decide that DDT exposure is unrelated to breast cancer.
Previous studies of DDT and breast cancer assessed exposure later in life, after the time that animal studies indicate the window of maximum vulnerability may have passed.
The study, led by Barbara Cohn, was the first to obtain blood samples from young women. It included 133 women who developed breast cancer before age 50 and 133 women who did not. These women had donated blood samples between 1959 and 1967, at an average age of 26 years as part of a child health and development study.
Although a number of previous studies found no link between breast cancer and DDE, a compound produced when DDT breaks down, Cohn's findings do not contradict earlier research, said Marcella Warner, an expert in environmental and reproductive epidemiology at the University of California at Berkeley.
That is because those studies were looking at measured DDE instead of p,p'-DDT. In fact, previous studies may have misclassified exposure, added Warner, who was not affiliated with the study.
"One gets exposure to DDE through foods," Warner said. "A measure of DDE may be an indicator of current and past exposure to DDT but also a direct measure of DDE intake in foods."
"Many in the scientific and medical communities had concluded that DDT exposure does not cause breast cancer," said Cohn who directs the Center for Research on Women's and Children's Health at the Public Health Institute. "The publication of our study could re-open this debate."
DDT, dichlorodiphenyltrichlorethane, was widely used as a pesticide in the United States and other countries starting in the mid-1940s. The harmful impact of DDT on wildlife was the subject of "Silent Spring" (1962) by Rachel Carson. In 1972, DDT was banned for almost all uses in the United States.
Yet it has been proposed that DDT be reintroduced in the United States to control mosquitoes that carry West Nile Virus and some countries are using DDT to combat malaria.
"DDT has played in important role in malaria control, a pressing public health problem. However, in addition to cancer, the potential harmful effects of DDT that have been reported include reproductive problems such as premature birth and breastfeeding problems. The possible side effects of DDT for wildlife and humans should be recognized and a balanced view should be encouraged, including alternative methods of malaria control" said Cohn.
"Environmental Health Perspectives" is published by the National Institute of Environmental Health Sciences.
OPEN ACCESS: DDT and Breast Cancer in Young Women: New Data on the Significance of Age at Exposure [Environmental Health Perspectives; Subscribe]
Background: Previous studies of DDT and breast cancer assessed exposure later in life when the breast may not have been vulnerable, after most DDT had been eliminated, and after DDT had been banned.
Objectives: We investigated whether DDT exposure in young women during the period of peak DDT use predicts breast cancer.
Methods: We conducted a prospective, nested case-control study with a median time to diagnosis of 17 years using blood samples obtained from young women during 1959-1967. Subjects were members of the Child Health and Development Studies, Oakland, California, who provided blood samples 1-3 days after giving birth (mean age, 26 years) . Cases (n = 129) developed breast cancer before the age of 50 years. Controls (n = 129) were matched to cases on birth year. Serum was assayed for p,p·-DDT, the active ingredient of DDT ; o,p·-DDT, a low concentration contaminant ; and p,p·-DDE, the most abundant p,p·-DDT metabolite.
Results: High levels of serum p,p·-DDT predicted a statistically significant 5-fold increased risk of breast cancer among women who were born after 1931. These women were under 14 years of age in 1945, when DDT came into widespread use, and mostly under 20 years as DDT use peaked. Women who were not exposed to p,p·-DDT before 14 years of age showed no association between p,p·-DDT and breast cancer (p = 0.02 for difference by age) .
Conclusions: Exposure to p,p·-DDT early in life may increase breast cancer risk. Many U.S. women heavily exposed to DDT in childhood have not yet reached 50 years of age. The public health significance of DDT exposure in early life may be large.
ABSTRACT: Women's Interest in Gene Expression Analysis for Breast Cancer Recurrence Risk [Journal of Clinical Oncology]
Purpose: Genomic and other technologies are improving the accuracy with which clinicians can estimate risk for recurrence (RFR) of breast cancer and make judgments about potential benefits of chemotherapy. Little is known of how patients will respond to genomic RFR testing or interact with their physicians to make informed decisions regarding treatment. We assessed