Octamer-binding transcription factor 4, OCT-4, is a transcription factor protein that is encoded by the Pou5f1 gene and is part of the POU (Pit-Oct-Unc) family. OCT-4 consists of an octamer motif, a particular DNA sequence of AGTCAAAT that binds to their target genes and activates or deactivates certain expressions. These gene expressions then lead to phenotypic changes in stem cell differentiation during the development of a mammalian embryo. It plays a vital role in determining the fates of both inner mass cells and embryonic stem cells and has the ability to maintain pluripotency throughout embryonic development. Recently, it has been noted that OCT-4 not only maintains pluripotency in embryonic cells but also has the ability to regulate cancer cell proliferation and can be found in various cancers such as pancreatic, lung, liver and testicular germ cell tumors in adult germ cells. Another defect this gene can have is dysplastic growth in epithelial tissues which are caused by a lack of OCT-4 within the epithelial cells.