POU5F1 and teratoma: Among immunomarkers of germ cells, OCT3/4 is a transcription factor essential for stem cell functions that aids in their identification in tumors such as germinomas (GCNIS, seminomas, and dysgerminomas) and gonadoblastoma, but it is reduced in more differentiated germ cell tumors, for example, yolk-sac tumors and teratomas (Cheng et al., 2004; Jones et al., 2004).