Cumulative evidence has demonstrated the presence of cancer stem cells (CSC) in
breast cancer and its putative role in
cancer progression. Nonetheless, the clinical significance of CSC in
breast cancer remains elusive. The underlying reasons could be due to the heterogeneity of
breast cancer subtypes as well as different markers used to define breast CSC. In this study, three widely used markers (
aldehyde dehydrogenase (ALDH)1+ and CD24-CD44+) were used to define two populations of CSC in a large cohort of breast
cancers. The expressions of these markers were correlated with different clinicopathological features and the molecular subtypes. ALDH1+ breast
cancers were associated with basal-like and HER2-overexpressing subtypes and the characteristics histologic features were related to these two subtypes. On the other hand, CD24-CD44+ breast
cancers were associated positively with the presence of extensive in situ component, the absence of lymph node involvement, and basal markers, but negatively with HER2. CD24-CD44+ breast
cancers were also positively associated with
luminal B
cancers. As the expression of CSC markers varied among different molecular subtypes and different clinicopathological features, it appeared that each CSC population could have distinct clinical values in different subgroups of breast
cancers. For improved prognostication with CSC, combining the analysis of CSC markers would be required. Within the
luminal cancers, CSC appeared to identify
cancers with poor outcome. The presence of CSC populations was associated with ER-PR+
cancers and
tumors expressing basal markers. Basal marker expression can
complement with CSC for improved
indicator for poor prognosis in
luminal breast
cancers. For the first time, the possible contribution of CSC to these aggressive
luminal cancers was demonstrated. The association of basal features and CSC in
luminal cancers also raised the possibility that
luminal cancer cells may acquire basal phenotype and CSC properties together during their progression.