For instance, SGCTs and embryonal carcinoma, which contain undifferentiated cells that resemble PCGs or ESCs, are associated with high NANOG expression levels, while teratomas, yolk sac tumors and choriocarcinomas have low levels or do not express NANOG at all, as their cells are more differentiated (Vega et al., 2012; Buljubašić et al., 2018). Here, NANOG is linked to yolk sac tumor.