MAGEA4 and cancer: We furthermore examined MAGE-A4 and NY-ESO-1 [41], two representatives of the germ cell-specific "cancer/testis" gene family on the X-chromosome, which appear in gonocytes from around gestational week 17–18 at differentiation into pre-spermatogonia, and are expressed in adult spermatogonia and primary spermatocytes, as well as in some testicular tumours and a broad range of somatic cancers [42,43].