Finally, to analyze the claim that ALDHbr cells are key tumorigenic cells in HER2-OE breast cancer [14,26], we compared the mRNA expression of the aforementioned key markers genes for pluripotency, proliferation and EMT/metastasis between the CD44−/low/CD24−/low and ALDHbr subpopulations from the HER2-OE cell lines BT-474 and AU-565. The gene discussed is ERBB2; the disease is breast carcinoma.