SOX2 and cancer: The status of stem cell markers has been quantified by the extent of tumor spheroid formation and by the expression status of select molecules, such as clusters of differentiation CD44, CD133 and nuclear transcription factors octamer-binding transcription factor-4 (OCT-4), Kruppel-like factor-4 (Klf-4), sex determining region box Y-2 (Sox-2), cellular Myc (c-Myc) and DNA-binding transcription factor NANOG in cancer stem cell models [22,27,28,29].