Pubertal growth and adult height in relation to breast cancer risk in African American women.

Adult height has been positively associated with breast cancer risk. The timing of pubertal growth-as measured by age at menarche and age at attained height-may also influence risk. We evaluated associations of adult height, age at attained height, and age at menarche with incidence of invasive breast cancer in 55,687 African American women in the prospective Black Women's Health Study. Over 20 years, 1,826 invasive breast cancers [1,015 estrogen receptor (ER) positive; 542 ER negative] accrued. We used multivariable Cox proportional hazards regression to estimate hazards ratios (HRs) and 95% confidence intervals (CIs) for associations with breast cancer overall and by ER status, mutually adjusted for the three factors of interest. Adult height was associated with increased risk of ER+ breast cancer (HR for ≥70 inches vs ≤63 inches: 1.44; 95% CI: 1.09, 1.89) but not ER- (corresponding HR: 1.16; 95% CI: 0.78, 1.71) (p heterogeneity = 0.34). HRs for attained height before age 13 versus age >17 were 1.30 (95% CI: 0.96, 1.76) for ER+ and 1.25 (95% CI: 0.80, 1.96) for ER- breast cancer. Results for age at menarche (≤11 vs ≥14 years) were similar for ER+ and ER- breast cancer (HR for breast cancer overall: 1.30; 95% CI: 1.12, 1.50). We confirmed height as a strong risk factor for ER+ breast cancer in African American women and identified early age at attained height as a risk factor for both ER+ and ER- breast cancer, albeit without statistical significance of the latter associations. While adult height and timing of pubertal growth are inter-related, our findings suggest that they may be independent risk factors for breast cancer.