Clinicopathological significance of cancer stem cell markers CD44 and ALDH1 expression in breast cancer

Background CD44 and aldehyde dehydrogenase 1 (ALDH1) has been reputed to be cancer stem cell (CSC) markers in breast cancer. Yet, the clinicopathologic and prognostic significance of these markers remain unclear. In this study, we have investigated the expression of these markers and their relation with conventional clinicopathologic tumor characteristic including molecular subtype. Methods CD44 and ALDH1 expression were investigated by immunohistochemistry in a series of 157 formalin-fixed paraffin-embedded breast cancer tissues. Results Overall, CD44 and ALDH1 are, respectively, detected in 33% (52 of 157) and 7% (10 of 157) of breast cancer cases. We also observed that CD44 expression was associated with histological grade (p = 0.005). For ALDH1, we found that its expression is more frequent with elderly women (>50 years, p = 0.03). The investigation of relationship between the stem cell phenotype and breast cancer molecular subtype, revealed that CD44 and ALDH1 expression was more frequent in basal-like tumors (p = 0.005). Among the two cancer stem cell markers tested, ALDH1 showed a strong association with the basal marker EGFR (p = 0.05). Conclusions These findings suggest that CD44 and ALDH1 play a role in the clinical behavior in breast cancer and might be interesting biomarkers and therapeutic targets.