Background: We investigated the impact of breast cancer molecular subtypes and treatment on survival in a cohort of medically insured women followed for more than 20 years.

Methods: We examined 934 female members of an integrated health care delivery system newly diagnosed with invasive breast cancer between 1988 and 1995 and followed them through 2008. Tumors were classified into four molecular subtypes on the basis of their expression profile: luminal A; luminal B; basal-like; and HER2-enriched. We followed women from the surgery date to death, health plan disenrollment, or study's end. HR and 95% confidence intervals (CI) were fit using Cox proportional hazards models adjusting for cancer treatments and tumor characteristics.

Results: A total of 223 (23.9%) women died because of breast cancer during the 21-year study period. Compared with women with luminal A tumors, women with HER2-enriched (HR 2.56, 95% CI 1.53–4.29) and luminal B tumors (HR 1.96, 95% CI: 1.08–3.54) had roughly a two-fold increased adjusted risk of breast cancer mortality. In addition, the survival curves suggest that risk of late mortality persists in women with luminal A tumors.

Conclusion: Among women with health care coverage, molecular subtypes were important predictors of breast cancer mortality. Women with HER2-enriched tumors and luminal B subtypes had the poorest survival despite adjusting for important covariates.

Impact: In a cohort followed for more than 20 years, women with HER2-enriched tumors had worse survival, but interestingly, the survival curve for women with luminal A tumors continued to steadily decline after 10 years of follow-up. Cancer Epidemiol Biomarkers Prev; 21(10); 1848–55. ©2012 AACR.