Profiling of Breast Cancer Stem Cell Types/States Shows the Role of CD44^hi/CD24^lo-ALDH1^hi as an Independent...

Multiple markers exist for breast cancer stem cells (CSCs), which are believed to represent the phenotypes of various CSC types and/or states. The relationship between each CSC subpopulation/state and the primary hallmarks of cancer has not been sufficiently clarified. In this study, six CSC markers (CD44^hi/CD24^lo, CD24, Ep-CAM, ALDH1, CD10, and BMI1) were assessed in a surgical cohort of 73 breast cancer patients. The expression of a single or multiple CSC markers was correlated with clinicopathological parameters, including markers of immune evasion, proliferation, epithelial-mesenchymal transition (EMT), and survival. All CSC phenotypes, except for CD10, correlated with markers indicative of higher proliferation. The CD44^hi/CD24^lo phenotype correlated with markers of EMT and PD-L1 expression, unlike ALDH1^hi. Both Ep-CAM^hi and CD24^hi breast cancer were associated with indicators of immune evasion, including PD-L1 expression, and the infiltration of FOXP3+ and PD-1+ tumor-infiltrating lymphocytes (TIL). While the CD44^hi/CD24^lo, Ep-CAM^hi, and ALDH1^hi phenotypes correlated with shorter overall survival (OS), CD24^hi correlated with reduced disease-free survival (DFS). Interestingly, among all tested CSC markers, the CD44^hi/CD24^lo-ALDH1^hi combination phenotype correlated with the worst DFS (HR 2.8, p = 0.014 in univariate/multivariate analysis) and OS (p < 0.001, HR 6.4 in univariate and 5.4 in multivariate analysis). A side-by-side comparison of multiple CSC markers demonstrated the differential linkage of CSC phenotype/state with distinct features of breast cancer. This comparison demonstrates the advantage of the CD44^hi/CD24^lo-ALDH1^hi combination marker for prognostication, especially after neoadjuvant chemotherapy. In the future, distinct markers of CSCs can hopefully be leveraged to trace/monitor different disease characteristics or treatment outcomes.