POU5F1 and neoplasm: In an effort to determine how the expression of core pluripotency-associated transcription factors—OCT4, NANOG, SOX2, KLF4, and c-MYC—correlates with tumor aggressiveness, Porath and colleagues found that the expression of ESC transcription regulators in tumors was negatively correlated with the degree of tumor differentiation (Ben-Porath et al., 2008).