BACKGROUND : Uterine leiomyomata, or fibroids, are hormone-dependent neoplasms of the myometrium that can cause severe gynecologic morbidity. In previous studies, incidence of these lesions has been positively associated with exposure to polychlorinated biphenyls (PCBs), a class of persistent endocrine-disrupting chemicals. However, previous studies have been retrospective in design and none has used ultrasound to reduce disease misclassification.

METHODS : The Study of Environment, Lifestyle, and Fibroids is a prospective cohort of 1,693 reproductive-aged Black women residing in Detroit, Michigan (enrolled during 2010-2012). At baseline and every 20 months for 5 years, women completed questionnaires, provided blood samples, and underwent transvaginal ultrasound to detect incident fibroids. We analyzed 754 baseline plasma samples for concentrations of 24 PCB congeners using a case-cohort study design. We used multivariable Cox proportional hazards regression to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between plasma PCB concentrations and ultrasound-detected fibroids incidence over a 5-year period.

RESULTS : We observed little association between PCB congener concentrations and fibroid incidence. The HR for a one-standard deviation increase in log-transformed total PCBs was 0.94 (95% CI: 0.78, 1.1). The PCB congener with the largest effect estimate was PCB 187 (HR for a one-standard deviation increase in log-transformed exposure=0.88, 95% CI: 0.73, 1.1). Associations did not appear to vary strongly across PCB groupings based on hormonal activity.

CONCLUSIONS : In this cohort of reproductive-aged Black women, plasma PCB concentrations typical of the contemporary general population were not appreciably associated with higher risk of fibroids.