Post-diagnosis adiposity and survival among breast cancer patients: influence of breast cancer subtype

Purpose: Adiposity has been linked with increased breast cancer risk and mortality. It is established that etiologic associations for adiposity vary by tumor subtype, but the influence of adiposity on subtype-specific survival is unknown. Methods: Study participants were 1,109 invasive breast cancer participants in the population-based Carolina Breast Cancer Study, diagnosed between 1993 and 2001, and with tissue blocks available for immunohistochemical subtyping. General and central adiposities were assessed by body mass index (BMI) and waist-to-hip ratio (WHR), respectively, based on in-person measurements after diagnosis. Vital status as of 2011 was determined using the National Death Index (median follow-up = 13.5 years). Cox proportional hazards models were used to calculate hazard ratios (HRs) and 95 % confidence intervals (CIs) for breast cancer (BC)-specific and all-cause mortalities. Results: Among all patients, high WHR (≥0.84), but not BMI, was associated with all-cause mortality (adjusted HR 1.50, 95 % CI 1.11–2.05, <0.77 as reference). No significant association between adiposity and BC-specific mortality was detected, although there was a suggestion of increased mortality risk among high-BMI (≥30 kg/m²) patients with basal-like tumors (adjusted HR 2.44, 95 % CI 0.97–6.12, <25 kg/m² as reference). Quantitative differences in all-cause mortality were observed by subtype, with BMI associated with basal-like mortality and WHR associated with luminal mortality. The associations were attenuated by tumor characteristics. Conclusions: Our study confirms the association of adiposity and unfavorable overall survival in breast cancer patients and suggests that this association may vary by intrinsic subtype and adiposity measure.