CD44 and breast cancer: There are plenty of common or unique surface markers that have been associated with solid or hematopoietic tumors, for example, CD34+CD38− for AML [4]; CD44+CD24−/lowLin- [5] and ALDH+ [10] for breast cancer; CD44+ [11], CD44+α2β1+ [12] and ALDH+ [13] for prostate cancer; CD44+CD117+ [7], CD24+ [14], ALDH+ [15] and CD133+ [16] for ovarian cancer.