Biomarker analysis by breast cancer phenotype in African-American versus Caucasian patients: Correlates with survival

Abstract

10551 Background: Breast carcinomas in African-American (AA) patients (pts) have poorer prognosis and higher likelihood of aggressive basal phenotype (triple negative for ER, PR, HER2) than those in Caucasian (C) patients (Carey et al, JAMA 2006, 295(21):2492; Morris et al, Breast Cancer Res Treat 2006, abstr 3055). We have additionally examined biomarker expression by phenotype in AA pts in our registry to further explain more aggressive behavior in this population. Methods: Stage, grade, ER, PR, Ki-67, HER2, and p53 expressions were compiled for breast carcinomas in 2,230 AA and C pts diagnosed between 1995–2004. Immunohistochemical markers were assayed using antibodies to the above proteins on paraffin-embedded formalin-fixed tissue. Differences in expression were analyzed by Chi- squared and Wilcoxon tests, and survival by Kaplan-Meier estimates. Results: AA pts have higher propensity for basal phenotype breast cancers (20.8% vs 10.4%, p<0.001) and lower propensity for Luminal A/B (ER+/PR+-/HER2-) phenotype (44.2% vs. 54.1%, p<0.001) as compared with C pts. Higher ki-67 proliferation index was found in AA pts (86.4% vs 78.8% in basal, p=0.3423; 37.1% vs. 26.7% in Luminal A/B p=0.0233) as compared with C pts. p53-positivity was higher in AA and C pts in all cases (p=0.0158), higher in AA pts with basal phenotype (p=0.2597), but identical in AA and C pts with luminal phenotypes (p=0.881). Survival was similar in basal phenotypes between races in all cases stage for stage, and controlled for ki-67 and p53 status, with a trend toward poorer survival among luminal phenotypes between races. Conclusions: AA pts have higher propensity for basal phenotype breast cancers than C pts, with higher ki-67 expression in both basal and luminal phenotypes, and higher p53 expression in basal phenotype, but these do not correlate with significant differences in survival by phenotype between races. As neither ki-67 index nor p53 expression can therefore solely explain differences in survival rates seen between races, molecular array studies between races and matched by phenotype are proposed. [Table: see text]