CD44 and breast cancer: Previous studies suggested that the prevalence of CD24-/CD44+ CSCs in breast tumors was linked to distant metastasis.51 In contrast, not all breast cancer cell lines containing high percentages of CD24-/CD44+ CSCs could give rise to lung metastasis.27 In addition, analyses of breast cancer samples showed that total CD44 expression can't predict distant metastasis efficaciously (Figure 5f and Supplementary Figure 7A).