POU5F1 and cancer: Two hypotheses can be drawn from the phenomenon: (1) dedifferentiation of fully differentiated cancer cells may have occurred during carcinogenesis, which reactivated the miR-302/367 cluster activity and (2) a proportion of cancer cells may have gained the ability to transcribe the miR-302/367 cluster, probably due to the production of Oct4 or Sox2 (known to bind to the promotor region of miR-302a [26]), and later dominated.