The Association of Serum Phthalates and Parabens with Mammographic Breast Density

Humans are exposed to a large number of environmental chemicals which have estrogenic activity, raising concern regarding potential effects on breast tissue and breast cancer risk. Phthalates are commonly found in personal care products, such as shampoos, lotions, and shaving products, and are present in many consumer plastics, adhesives, detergents, and pharmaceuticals. Parabens are also found in personal care products, and are additionally used as antimicrobials in foods. In vitro studies have demonstrated that many phthalates and parabens can bind to the estrogen receptor and initiate estrogenic cellular pathways, and a recent case-control study found that urinary concentrations of mono-ethyl-phthalate were positively associated with breast cancer risk. We examined the cross-sectional association of circulating serum levels of phthalates and parabens with mammographic breast density (a marker for breast cancer risk). A total of 261 postmenopausal women (ages 55–70, with no history of postmenopausal hormone use) were recruited from mammography clinics in Madison, Wisconsin. Patients completed a questionnaire regarding known breast cancer risk factors and provided a blood sample that was analyzed for mono-ethyl-phthalate, mono-butyl-phthalate, mono-benzyl-phthalate, butyl paraben, and propyl paraben. Percent breast density was measured from patients' mammograms as a continuous variable using a computer-assisted thresholding method (Cumulus software). After adjusting for age and body mass index, mono-ethyl-phthalate was positively associated with percent breast density. Women with detectable mono-ethyl-phthalate levels (>0.4 ng/mL; N = 36) had higher percent breast density than women with no detectable mono-ethyl-phthalate (N = 225) in their serum (16.8% vs. 12.8%; P = 0.03). Serum levels of mono-butyl-phthalate and mono-benzyl-phthalate were generally below the limits of detection. Serum levels of butyl-paraben and propyl-paraben were higher (detectable in 55% and 67% of patients, respectively), but neither was associated with breast density (P > 0.20). These results suggest that further investigation into the potential influence of mono-ethly-phthalate (and its parent compound diethyl-phthalate) on breast tissue is warranted.