ESA can distinguish luminal, basal, and stem-like cells. Presented are representative flow cytometry dot plots of epithelial-specific antigen (ESA) and CD24 expression adjacent to ESA immunofluorescence of each cell line subtype. Cell lines are as follows: (a) luminal-like, expressing high levels of ESA and CD24 (MCF7, SUM225, and T47D); (b) basal-like, expressing low levels of ESA and CD24 (SUM159, SUM1315, and MDA.MB.231); or (c) mixed luminal/basal cultures that contain both ESA+/CD24+ and ESA-/CD24- populations (SUM149). (d) The average percentage of CD44+/CD24-/ESA+ cells in each cell line, as determined by flow cytometry. Data are presented as the mean ± stamdard error of the mean for five separate experiments. HMEC, human mammary epithelial cells.