Several cell surface markers, including CD24, CD44, Nanog, CD90, CD133, SOX2, SOX9, ESA, and KLF4, have been successfully used in the past to identify CSC subpopulations phenotypically in cell culture and clinical samples from a variety of cancer types [123, 132–134]; unfortunately, due to their lack of organ specificity, these markers frequently also identify normal SCs, necessitating the hunt for additional markers the more thoroughly and properly to define CSCs. This evidence concerns the gene CD44 and cancer.