To investigate the stem properties of different subtype, we compared the expression of CD44, CD24 and ALDH1 in four human breast cancer cell lines using flow cytometry analysis and immunostaining: MCF-7 (luminal A), SK-BR-3 (HER2-OE), MDA-MB-468 (basal epithelial), and MDA-MB-231 (basal mesenchymal, triple-negative)32,33. Here, ALDH1A1 is linked to breast cancer.