Abstract
BACKGROUND: During puberty, mammary tissue undergoes rapid development, which provides a window of heightened susceptibility of breast composition to the influence of endogenous and exogenous hormones. Exposure to endocrine-disrupting chemicals (EDC) may affect breast development and composition and the risk of developing breast cancer in adulthood. METHODS: We evaluated the associations between breast density and urinary concentrations of phenols and phthalates collected at Tanner 1 (B1) and Tanner 4 (B4) in 200 Chilean girls. Total breast volume (BV), fibroglandular volume (FGV), and percent dense breast (%FGV) were evaluated at B4 using dual X-ray absorptiometry. Generalized estimating equations were used to analyze the association between concentrations of EDC biomarkers across puberty and breast density. RESULTS: The geometric mean %FGV was 7% higher among girls in the highest relative to the lowest tertile of monocarboxyisooctyl phthalate [1.07; 95% confidence interval (CI), 1.01-1.14]. Monoethyl phthalate concentrations at B4 were positively associated with FGV (highest vs. lowest tertile: 1.22; 95% CI, 1.06-1.40). Bisphenol A displayed a U-shaped association with FGV; girls in the middle tertile had at least 10% lower FGV than girls in the lowest or highest tertiles. Monocarboxyisononyl phthalate showed a nonlinear association with BV. No other statistically significant associations were observed. CONCLUSIONS: Our results suggest that the developing breast tissue is susceptible to select EDCs during childhood and adolescence. IMPACT: This study may spur further investigations into environmental influences on breast development during puberty and how shifts in pubertal breast density track through the life course to modify breast cancer risk.