SOX2 and cancer: Additionally, the downregulation of YBX1 in basal-like breast cancer cell lines MDA-MB-231 and BT549 is strongly correlated with a significant reduction in the mRNA expression levels of cancer stem cell genes, including POU Domain Transcription Factor OCT4, Homeobox Transcription Factor Nanog, and SOX2 (SRY-Box Transcription Factor 2) [99].