Racial Differences in PAM50 Subtypes in the Carolina Breast Cancer Study

J Natl Cancer Inst. 2018 Feb 1;110(2):176-182. doi: 10.1093/jnci/djx135.


Background: African American breast cancer patients have lower frequency of hormone receptor-positive (HR+)/human epidermal growth factor receptor 2 (HER2)-negative disease and higher subtype-specific mortality. Racial differences in molecular subtype within clinically defined subgroups are not well understood.

Methods: Using data and biospecimens from the population-based Carolina Breast Cancer Study (CBCS) Phase 3 (2008-2013), we classified 980 invasive breast cancers using RNA expression-based PAM50 subtype and recurrence (ROR) score that reflects proliferation and tumor size. Molecular subtypes (Luminal A, Luminal B, HER2-enriched, and Basal-like) and ROR scores (high vs low/medium) were compared by race (blacks vs whites) and age (≤50 years vs > 50 years) using chi-square tests and analysis of variance tests.

Results: Black women of all ages had a statistically significantly lower frequency of Luminal A breast cancer (25.4% and 33.6% in blacks vs 42.8% and 52.1% in whites; younger and older, respectively). All other subtype frequencies were higher in black women (case-only odds ratio [OR] = 3.11, 95% confidence interval [CI] = 2.22 to 4.37, for Basal-like; OR = 1.45, 95% CI = 1.02 to 2.06, for Luminal B; OR = 2.04, 95% CI = 1.33 to 3.13, for HER2-enriched). Among clinically HR+/HER2- cases, Luminal A subtype was less common and ROR scores were statistically significantly higher among black women.

Conclusions: Multigene assays highlight racial disparities in tumor subtype distribution that persist even in clinically defined subgroups. Differences in tumor biology (eg, HER2-enriched status) may be targetable to reduce disparities among clinically ER+/HER2- cases.

MeSH terms

  • Adult
  • Aged
  • Black or African American*
  • Breast Neoplasms / chemistry*
  • Breast Neoplasms / ethnology*
  • Breast Neoplasms / genetics
  • Breast Neoplasms / pathology
  • Cell Proliferation
  • Female
  • Humans
  • Middle Aged
  • RNA, Neoplasm / analysis*
  • Receptor, ErbB-2 / analysis*
  • Receptors, Estrogen / analysis*
  • Receptors, Progesterone / analysis*
  • Recurrence
  • Tumor Burden
  • White People*
  • Young Adult


  • RNA, Neoplasm
  • Receptors, Estrogen
  • Receptors, Progesterone
  • ERBB2 protein, human
  • Receptor, ErbB-2