Outcome disparities in African American women with triple negative breast cancer: a comparison of epidemiological and molecular factors between African American and Caucasian women with triple negative breast cancer

Abstract

Background: Although diagnosed less often, breast cancer in African American women (AAW) displays different characteristics compared to breast cancer in Caucasian women (CW), including earlier onset, less favorable clinical outcome, and an aggressive tumor phenotype. These disparities may be attributed to differences in socioeconomic factors such as access to health care, lifestyle, including increased frequency of obesity in AAW, and tumor biology, especially the higher frequency of triple negative breast cancer (TNBC) in young AAW. Improved understanding of the etiology and molecular characteristics of TNBC in AAW is critical to determining whether and how TNBC contributes to survival disparities in AAW.

Methods: Demographic, pathological and survival data from AAW (n = 62) and CW (n = 98) with TNBC were analyzed using chi-square analysis, Student's t-tests, and log-rank tests. Frozen tumor specimens were available from 57 of the TNBC patients (n = 23 AAW; n = 34 CW); RNA was isolated after laser microdissection of tumor cells and was hybridized to HG U133A 2.0 microarrays. Data were analyzed using ANOVA with FDR <0.05, >2-fold difference defining significance.

Results: The frequency of TNBC compared to all BC was significantly higher in AAW (28%) compared to CW (12%), however, significant survival and pathological differences were not detected between populations. Gene expression analysis revealed the tumors were more similar than different at the molecular level, with only CRYBB2P1, a pseudogene, differentially expressed between populations. Among demographic characteristics, AAW consumed significantly lower amounts of caffeine and alcohol, were less likely to breastfeed and more likely to be obese.

Conclusions: These data suggest that TNBC in AAW is not a unique disease compared to TNBC in CW. Rather, higher frequency of TNBC in AAW may, in part, be attributable to the effects of lifestyle choices. Because these risk factors are modifiable, they provide new opportunities for the development of risk reduction strategies that may decrease mortality by preventing the development of TNBC in AAW.

Figure 1

Survival analysis of AAW and CW with TNBC. Red line = AAW, blue line = CW. Statistical analysis by both log-rank (P = 0.9469) and Wilcoxen (P = 0.7273) testing failed to detect significant differences in survival between populations.

Figure 2

Principal component analysis of TNBC from AAW (n = 23) and CW (n = 34). Orange spheres = CW tumors, red spheres = AAW tumors.

Figure 3

Gene expression of probe 206777_s_at representing CRYBB2P1. Red ovals = expression in AAW, orange ovals = expression in CW. Expression levels were 3.9-fold higher in AAW compared to CW, with 8/22 AAW having expression levels similar to CW.