HER2-expressing breast tumors are associated with breast cancer stem-cell phenotype CD44+/CD24

INTRODUCTION: According to the cancer stem-cell theory, tumors originate from a small population of cancer stem cells, which lose the mechanism of self-regulation and begin to differentiate and proliferate indefinitely. The CD44+/CD24- phenotype may be considered a stem-cell marker in breast cancer. OBJECTIVE: To evaluate the correlation between CD44+/CD24- phenotype and different molecular subtypes of breast cancer in invasive ductal carcinoma samples. METHODS: The expression of CD44, CD44v6, and CD24 markers was investigated in 133 cases of invasive mammary carcinoma with immunohistochemistry. CD44+/CD24- phenotype was identified and correlated with the molecular subtypes and classical prognostic factors such as age, histological grade, tumor size, and lymph node status. RESULTS: Eighteen (14%) cases were positive for CD44+/CD24- (CD44+/CD24- or CD44v6+/CD24-) phenotype; among these, 11.1%, 27.8%, 38.9%, and 22.2% were luminal, luminal B-human epidermal growth factor receptor 2 (HER2), HER2, and triple-negative subtype, respectively. CD44+/ CD24- phenotype was more common in HER2 subgroup (p = 0.0197). CONCLUSION: CD44+/CD24- phenotype was correlated with molecular subtypes of breast cancer. The highest expression of CD44+/CD24- phenotype was reported in patients with HER2+ disease, a molecular subtype associated with more aggressive behavior and worse prognosis.