POU5F1 and cancer: Cancer cells (especially cancer stem cells) share some characteristics with ESCs and induced pluripotent cells: replicative immortality, increased proliferative capacity, expression of OCT4, NANOG, and KLF4 (factors that induce cellular reprogramming, or are fundamental for maintaining a pluripotent state and are also potent oncogenes), and telomerase activation [19,65].