NANOG and teratoma: In line with this finding, we already demonstrated that NANOG expression is regulated by DNA methylation in GCTs, with NANOG‐negative aYSTs harbouring with 70% the highest levels of NANOG promotor DNA methylation of all analysed GCT tissues (3.8% in seminomas, 6% in ECs, 66% teratomas and 62% choriocarcinomas).50