Overexpression of SATB1 in the breast cancer cell line MCF-7 was demonstrated to increase the population, which was measured by mammosphere formation and CD44+/CD24− expression in vitro and formation of tumors in SCID model mice (in vivo). Downregulation of SATB1 in the breast cancer cell line BT-549 resulted in the opposite result. This evidence concerns the gene CD44 and breast cancer.