CD44+/CD24-/ESA+ cells preferentially survive chemotherapy. (a) Quantification of viable CD44+/CD24-/ESA+ cells in various human breast cancer cell lines following a 6-day treatment with 10 nmol/l paclitaxol (Taxol) or 1 mm 5-fluorouracil (5-FU). Data are presented as the mean ± standard error of the mean for four separate experiments. (b) SUM159 cells were continuously treated with BrdU for 10 days and chased with media containing 10 nmol/l Taxol or 1 mmol/l 5-FU. On day 6 of the chase, cells were stained for 5-bromo-2-deoxyuridine (BrdU) and counted for the solid (complete label retention) and speckled (partial label retention) staining. DMSO, dimethyl sulfoxide.