(ChemotherapyAdvisor) – African American women have worse survival from breast cancer compared with other racial and ethnic groups, as well as less treatable types of the disease; however, the higher mortality observed cannot be attributed entirely to differential diagnosis by subtype, according to a study presented at the American Association for Cancer Research (AACR) Annual Meeting 2013, in Washington, DC.

“The results seem to indicate that although African American women are more likely to be diagnosed with less treatable subtypes of breast cancer compared with white women, it is not the only reason they have worse breast cancer mortality,” said Candyce Kroenke, MPH, ScD, a research scientist at Kaiser Permanente Division of Research, Oakland, CA.

Dr. Kroenke and colleagues examined associations between race and breast cancer survival by PAM50 breast cancer subtypes (luminal A, luminal B, basal-like, HER2 enriched) in a prospective cohort of 1,688 breast cancer survivors from the Life After Cancer Epidemiology (LACE) and Pathways cohorts.

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“Self-reported race was obtained at study entry from mailed questionnaires,” the investigators reported. They obtained 1-mm punches from areas of representative tumor in formalin-fixed, paraffin-embedded tumor blocks and determined expression of the PAM50 genes for molecular subtype by reverse transcriptase polymerase chain reaction of extracted RNA.

After a median follow-up of 6.3 years (range, 0.3-15.5 years), 499 women had died, 268 from breast cancer. Consistent with previous research, breast cancer was significantly higher in African American women (hazard ratio [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 white women. African American women also had a lower likelihood of luminal A (odds ratio [OR],R 0.61; 95% CI: 0.38-0.98) and luminal B (OR, 0.43; 95% CI: 0.23-0.82) breast cancer subtypes and a greater likelihood of the less treatable basal subtype (OR, 2.93; 95% CI: 1.94-4.44), they found.

Asian women were less likely to be diagnosed with 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).

“African Americans were more likely to have the hard-to-treat triple-negative breast cancer subtype and had a lower likelihood of having the luminal A subtype, which tends to be the most treatable subtype of breast cancer and has the best prognosis,” Dr. Kroenke said.

“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,” they concluded.