CD44 and breast cancer: Since it has been reported that hypoxia exposure alone can increase the stem-like cell population, we also examined the percentage of CD44+/CD24-/ESA+ and CD44+/CD24+/ESA+ cell populations in the hypoxia-exposed adherent cells (MDA-MB 231 A3 and BCM2 A3) and found only a slight increase in the percentage of CD44+/CD24-/ESA+ cell population in the hypoxia-exposed adherent cells compared with the parental breast cancer cell lines (1.8-fold increase in MDA-MB 231 A3 cells, Figure 3c; 3.5-fold increase in BCM2 A3, Figure 3c).