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Exposure to high levels of DDT is known to increase risk of breast cancer and new research examined whether age of exposure and of diagnosis are connected. The population studied for the report, which appears in The Journal of the National Cancer Institute, was postmenopausal women aged 50 to 54.
The prospective, nested case-control study was a follow-up to the 2007 Child Health and Development Studies (CHDS) report. CHDS is a six-decade-long effort that enrolled 15,528 women receiving obstetric care in the San Francisco East Bay area and tracked age at first DDT exposure, DDT levels at pregnancy, and age when breast cancer was diagnosed. For the new analysis, researchers extended their observation to cases diagnosed at ages 50 to 54. They used conditional logistic regression to estimate DDT associations with breast cancer in birth year-matched case-controlled sets.
In the follow-up study, researchers found that a woman’s first exposure to DDT was associated with the timing of her breast cancer diagnosis (approximately 40 years later). Women first exposed to DDT before age 14 had a significant risk of being diagnosed with breast cancer before age 50 (OR = 5.42, 95% CI: 1.71-17.19). In contrast, in women with exposure after age 14, breast cancer risk was only increased after menopause (OR = 2.17, 95% CI: 1.13-4.19).
The authors said their findings support previous research on DDT and breast cancer and point to a susceptibility window for DDT, which appears to be an endocrine disruptor to which the breast responds from in utero to menopause. The major limitation of the study was inability to estimate the contribution of genetic susceptibility but the findings may be helpful to ob/gyns in developing better treatment and observation plans for patients exposed to DDT.