The CD44+/CD24- subpopulation was believed to be putative stem cells in human breast tissue, enriched for basal cells and motility genes, which could be generated during the epithelial-mesenchymal transition. Moreover, these cells were negative for mucin 1, estrogen receptor (ER), and v-erb-b2 erythroblastic leukemia viral oncogene homolog 2 (erbB2) receptor. More importantly, high expression of CD44+/CD24- cancer cells was associated with poor patient prognosis. These cells had the phenotype of cancer cells during the epithelial to mesenchymal transition, indicating that the gene expression pattern of CD44+/CD24- cells in breast cancers resembled more closely the pattern observed in CD44+/CD24- cells in normal breast than that of CD44-/CD24+ cells isolated from the same tumor. Taken together, these findings indicated that CD44+/CD24- cells, especially those expressing epithelial cell adhesion molecule, were breast cancer stem cells (CSCs).