Abstract 131: Race and breast cancer prognosis by PAM50 subtype in the LACE and Pathways studies.
Authors: Kroenke Candyce , Kwan Marilyn , Bernard Philip , Castillo Adrienne , Davis Carole , Factor Rachel , Habel Laurel , Kushi Larry , Quesenberry Charles , Shakespear Kaylynn , Stijleman Inge , Sweeney Carol , Weltzien Erin , Caan Bette 
Published: August 2014

Background: African-Americans have poorer breast cancer (BC) prognosis, and Asians and Hispanics have better prognosis, compared with Whites. The Black-White difference is unexplained and has been attributed to diagnosis with less treatable tumor subtypes in African-Americans. However, little research has examined whether race-survival differences exist by breast cancer subtype. Therefore, we examined associations between race and BC survival by PAM50 breast cancer subtypes (luminal A, luminal B, basal-like, HER2 enriched) in a prospective cohort of 1,282 breast cancer survivors from the Life After Cancer Epidemiology and Pathways cohorts.

Methods: Self-reported race was obtained at study entry from mailed questionnaires. 1 mm punches were obtained from areas of representative tumor in formalin-fixed, paraffin-embedded tumor blocks. Expression of the PAM50 genes for molecular subtype was determined by RT-PCR of extracted RNA. After a median 6.3 years of follow-up (range 0.3-15.5 years), 213 deaths, with 118 from breast cancer, were reported. Delayed entry Cox proportional hazard models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI) of BC mortality, controlling for time from diagnosis to enrollment, socioeconomic status, BC severity, BC subtype, treatment, and other known prognostic factors. Logistic regression was used to evaluate associations between race and subtype. Survival analyses stratified by subtype were adjusted for age, time from diagnosis to enrollment, BC severity, and BC treatment.

Results: Consistent with previous research, adjusted for stage and breast cancer treatment, BC mortality was significantly higher in African-Americans (HR=2.90, 95% CI: 1.74-4.86) and lower in Latinas and Asians (HR=0.51, 95% CI: 0.26-0.99), compared with Whites. In addition, compared with Whites, African-Americans had a lower likelihood of the luminal A (OR=0.61, 95% CI: 0.38-0.98) and luminal B (OR=0.43, 95% CI: 0.23-0.82) subtypes and a greater likelihood of the less treatable basal subtype (OR=2.93, 95% CI: 1.94-4.44). Asians were less likely to be diagnosed with the basal subtype (OR=0.41, 95% CI: 0.23-0.71) and somewhat more likely to be diagnosed with the HER2-enriched subtype (OR=1.47, 95% CI: 0.97-2.21). Stratified by subtype, African-Americans had poorer prognosis among those with luminal A (HR=2.64, 95% CI: 0.93-7.49), luminal B (HR=2.20, 95% CI: 0.43-11.26), basal-like (HR=1.66, 95% CI: 0.78-3.54), and HER2 enriched (HR=3.25, 95% CI: 1.04-10.15) subtypes than Whites.

Conclusion: African-Americans had worse breast cancer survival than other racial/ethnic groups and had less treatable types of breast cancer. However, breast cancer mortality was higher in African-Americans across tumor subtypes, suggesting that the Black-White survival difference may not be attributable to differential diagnosis by subtype.

Citation Format: Candyce Kroenke, Marilyn Kwan, Philip Bernard, Adrienne Castillo, Carole Davis, Rachel Factor, Laurel Habel, Larry Kushi, Charles Quesenberry, Kaylynn Shakespear, Inge Stijleman, Carol Sweeney, Erin Weltzien, Bette Caan. Race and breast cancer prognosis by PAM50 subtype in the LACE and Pathways studies. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 131. doi:10.1158/1538-7445.AM2013-131