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

Racial Differences in PAM50 Subtypes in the Carolina Breast Cancer Study

Melissa A Troester  1 , Xuezheng Sun  1 , Emma H Allott  1 , Joseph Geradts  1 , Stephanie M Cohen  1 , Chiu-Kit Tse  1 , Erin L Kirk  1 , Leigh B Thorne  1 , Michelle Mathews  1 , Yan Li  1 , Zhiyuan Hu  1 , Whitney R Robinson  1 , Katherine A Hoadley  1 , Olufunmilayo I Olopade  1 , Katherine E Reeder-Hayes  1 , H Shelton Earp  1 , Andrew F Olshan  1 , Lisa A Carey  1 , Charles M Perou  1
Affiliations

Racial Differences in PAM50 Subtypes in the Carolina Breast Cancer Study

Melissa A Troester et al. J Natl Cancer Inst. .

Abstract

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.

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