POU5F1 and neoplasm: To assess whether cells expressing pluripotency factors like SOX2 behave as a CSC subpopulation with increased tumor-promoting ability, we made use of a lentiviral-based reporter system in which a composite SOX2/OCT4 response element (SORE6) coupled to a minimal cytomegalovirus (CMV) promoter controls the expression of GFP fluorescent reporter gene.