ABCG2 and cancer: One cancer stem cell marker SOX2 was up-regulated in HOS-R/DOXO compared to its parental line (log2 FoldChange 1.89, adjusted p value 6,45×10-04), while none of the cancer stem cell markers (SOX2, OCT4, SSEA4, NANOG and ABCG2) [14] were modified in MTX-resistant lines.