POU5F1 and neoplasm: In BCs, SOX2 expression has mainly been reported in basal-like subtypes, suggesting a role in conferring a less differentiated phenotype [36] and has been associated with potential tamoxifen resistance [37] A recent study by O Leis et al., which analyzed the expression of pluripotency genes (OCT4, NANOG and SOX2) by IHC in 158 BCs, demonstrated that Sox2+ tumors fell into the early stages (I-III) of tumor progression.