ASPO Abstracts
Pubertal timing and breast cancer risk in the Sister Study cohort
Category: Lifestyles Behavior, Energy Balance & Chemoprevention
Conference Year: 2020
Abstract Body:
Purpose: Earlier age at menarche is an established risk factor for breast cancer. While age at menarche has been
fairly stable over the past half-century, age at breast development (thelarche) has continued to decrease.
Recently, earlier age at thelarche and a longer time between thelarche and menarche (pubertal tempo) were
shown to be associated with increased breast cancer risk. Our objective was to examine breast cancer risk
associated with ages at thelarche, menarche and length of pubertal tempo in a prospective U.S. cohort.
Methods: Women ages 35-74 years without a history of breast cancer, but who had a sister previously diagnosed
with breast cancer, were enrolled in the Sister Study from 2003-2009 (N=50,884). At enrollment, participants
reported their ages at thelarche and menarche. We calculated pubertal tempo as age at menarche minus age at
thelarche. We estimated adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) using Cox proportional
hazards regression for each pubertal milestone and risk of invasive breast cancer or ductal carcinoma in situ. We
examined modification by birth cohort, race/ethnicity and weight relative to peers at 10 years of age.
Results: During follow-up (mean=9.3 years), 3295 eligible women were diagnosed with breast cancer. Ages at
thelarche and menarche were correlated (Spearman r=0.6). Early ages at thelarche (HR=1.23, 95% CI 1.03-1.46
for <10 years compared to 12-13 years) and menarche (HR=1.10, 95% CI 1.01-1.20 for <12 years compared to
12-13 years) were each positively associated with breast cancer risk. These associations did not vary by birth
cohort, race/ethnicity or childhood weight. Pubertal tempo was not associated with breast cancer risk. When
considering early thelarche (<10 years) and early menarche (<12 years) jointly, women with both had a 30%
greater risk of breast cancer compared to women with neither risk factor (95% CI 1.07-1.57).
Conclusions: Earlier ages at thelarche and menarche but not pubertal tempo were associated with increased
breast cancer risk. Although the time between thelarche and menarche may represent a vulnerable risk period, the
high correlation between self-reported ages at these events may have limited our ability to detect a breast cancer
risk associated with tempo.
Keywords: breast cancer, puberty, menarche, breast development