ASPO Abstracts
Early-life exposures and age at breast development in the Sister Study cohort
Category: Lifestyles Behavior, Energy Balance & Chemoprevention
Conference Year: 2021
Abstract Body:
Purpose: Early age at breast development (thelarche) has been associated with increased breast cancer risk.
Average age at thelarche has declined over time, but there are few established risk factors for early thelarche. We
examined associations between pre- and postnatal exposures and age at thelarche in a U.S. cohort of women
born between 1928 and 1974.
Methods: Breast cancer-free women ages 35-74 years who had a sister diagnosed with breast cancer were
enrolled in the Sister Study from 2003-2009 (N=50,884). At enrollment, participants reported their age at
thelarche, which we categorized as early (≤10 years), average (11-13 years), and late (≥14 years), as well as
information on early-life exposures. We estimated odds ratios (ORs) and 95% confidence intervals (CIs) for early
and late thelarche relative to average age at thelarche using polytomous logistic regression for each early-life
exposure, adjusted for birth cohort, race/ethnicity and family income level in childhood. We examined modification
by birth cohort, race/ethnicity, family income, relative weight at age 10, and extent of breast cancer family history
through stratification.
Results: Early thelarche was more common in recent birth cohorts and among non-Hispanic Black and Hispanic
women. Early thelarche (≤10 years) was associated with multiple prenatal exposures: gestational hypertensive
disorder (OR=1.25, 95% CI 1.09-1.43), maternal diethylstilbestrol (DES) use (OR=1.23, 95% CI 1.04-1.45),
maternal smoking during pregnancy (OR=1.20, 95% CI 1.13-1.27), and young maternal age (OR 1.30, 95% CI
1.16-1.47 for <20 vs 25-29 years). Being firstborn was also associated with early thelarche (OR=1.25, 95% CI
1.17-1.33). Low birthweight (<2500 vs 2500-3999g) was suggestively associated with both early (OR=1.06, 95%
CI 0.96-1.17) and late (OR=1.15, 95% CI 1.05-1.25) thelarche, as was use of soy formula in infancy (Early:
OR=1.10, 95% CI 0.93-1.30; Late: OR=1.07, 95% CI 0.92-1.25). Patterns were generally similar across strata of
modifiers of interest.
Conclusion: Associations between pre- and postnatal exposures and age at thelarche suggest that the early-life
environment may influence breast development and therefore may also affect breast cancer risk by altering the
timing of pubertal breast development.
Keywords: puberty, breast development, thelarche, early-life, prenatal exposures