A high-throughput immunohistochemical screen of many different types of human cancers demonstrated that OCT3/4 is a specific and highly informative diagnostic marker for seminomatous tumours, which are the malignant counterparts of PGCs/gonocytes, as well as embryonal carcinomas, the stem cell component of non-seminomas (Looijenga et al, 2003; de Jong et al, 2005). This evidence concerns the gene POU5F1 and embryonal carcinoma.