Breast cancer cell lines with BCSC properties. a Mammosphere formation assay in MCF7, SK-BR-3, MDA-MB-231, and HCC1937 cells. Images show representative mammospheres in each cell line at day 5 of incubation. Original magnification: ×200. b ALDEFLUOR assay in breast cancer cell lines (HCC1937, MDA-MB-231, MCF7, and SK-BR-3). The upper panels show the negative controls (cells treated with DEAB, a specific inhibitor of ALDH1). Based on the negative control, the gated area was assigned as ALDH1-positive. Percentages of ALDH1-positive cell populations of each cell lines are shown in the lower panels