- Stem cell pluripotency factor NANOG is expressed in human fetal gonocytes, testicular carcinoma in situ and germ cell tumours. Hoei-Hansen, C.E., Almstrup, K., Nielsen, J.E., Brask Sonne, S., Graem, N., Skakkebaek, N.E., Leffers, H., Rajpert-De Meyts, E. Histopathology (2005)