Abstract
Height and body size in childhood and young adulthood have been consistently associated with breast cancer risk; whether associations differ across molecular subtypes is unclear. In a pooled analysis of the Nurses' Health Studies, we prospectively examined the association of four exposures: height, body mass index (BMI) at the age of 18 years, childhood and adolescent somatotypes, with breast cancer risk according to molecular subtypes defined by immunohistochemical markers. We used multivariable-adjusted Cox proportional hazards regression to estimate HRs and 95% confidence intervals (CI). We identified 2,983 luminal A, 1,281 luminal B, 318 HER2-enriched, 408 basal-like, and 128 unclassified tumors. Height was positively associated with all subtypes (Pheterogeneity = 0.78). BMI at the age of 18 (Pheterogeneity = 0.001), childhood (Pheterogeneity = 0.51), and adolescent somatotype (Pheterogeneity = 0.046) were inversely associated, but with differences in magnitude of association. BMI at the age of 18 of ≥25 kg/m(2) (compared with 20-21.9 kg/m(2)) was associated with a 52% decreased risk of HER2-enriched (HR, 0.48; 95% CI, 0.26-0.91; Ptrend < 0.0001) and 39% reduced risk of basal-like tumors (HR, 0.61; 95% CI, 0.36-1.02; Ptrend = 0.008). Compared with the lowest category, women in the highest adolescent body size category were 71% less likely to develop HER2-enriched (HR, 0.29; 95% CI, 0.10-0.85; Ptrend = 0.0005) and 60% less likely to develop basal-like (HR, 0.40; 95% CI, 0.17-0.95; Ptrend = 0.0008). Height was positively associated with risk of all breast cancer molecular subtypes. BMI at 18 years and childhood and adolescent were inversely associated with risk of most breast cancer molecular subtypes with somewhat stronger associations with HER2-enriched and basal-like subtypes. Cancer Prev Res; 9(9); 732-8. ©2016 AACR.