Background/Aims Little information exists on breast cancer survival rates according to molecular profiles among different race/ethnic groups. We investigated the impact of molecular subtypes on breast cancer-specific survival by race/ethnicity in a large group of medically-insured women diagnosed with breast cancer.

Methods The cohort included 20,749 diverse Kaiser Permanente Southern California (KPSC) women diagnosed with breast cancer (AJCC Stage 0–IV) between 1996 and 2007, and followed through 2009. The women’s cancers were classified into four main molecular subtypes: luminal A (ER+ and/or PR+/HER2−); luminal B (ER+ and/or PR+/HER2+); basal-like (“triple negative”, ER−/PR−/HER2−); and HER2+/ER−. The outcome was breast cancer mortality. Follow-up began on the date of surgery and ended on date of death, health plan disenrollment, or study’s end. Hazard rate ratios (HR) and 95% confidence intervals (CI) were estimated using Cox proportional hazards models. We adjusted for age, tumor characteristics, cancer treatments, income, and comorbidity.

Results Of the 20,749 women, 65% were white non-Hispanic (n=13,487); 13% Black (n=2,697); 12% Hispanic (n=2,490); and 10% Asian (n=2,075). We observed 2,019 deaths (10%) deaths due to breast cancer over 14 years of follow-up. In all race/ethnic groups combined, breast cancer mortality was higher in women with basal-like (HR 2.90, 2.38–3.53) and HER2+/ER− (HR 1.98, 1.55–2.54) tumors compared to women with luminal A subtype (referent group). In addition, we examined breast cancer mortality in each molecular subtype, stratified by race/ethnic group. Among women with luminal A tumors, Black women were more likely to die of breast cancer (HR 1.53, 1.02–2.29) than white women (referent group). In women with luminal B tumors, South Asians had a 10-fold increase in breast cancer mortality (HR=10.57, 1.42–78.64) compared to whites; however, numbers were small and the confidence interval was wide. Among women with basal-like tumors, Black women had a greater mortality risk (HR 1.36, 1.02–1.82) compared to white women. In women with HER2+/ER− tumors, breast cancer mortality was similar across the race/ethnic groups. No other comparisons were significant.

Discussion Despite similar access to healthcare, we found survival disparities by race/ethnic groups within the luminal A, luminal B, and basal-like molecular subtypes of breast cancer.