Detection of alpha-fetoprotein mRNA in seminoma

The classic testicular tumor marker alpha-fetoprotein (AFP) is associated w ith nonseminomatous germ cell tumors, including embryonal carcinoma, yolk s ac tumor, and teratoma. AFP is not considered to be produced by pure semino ma. However, postmortem studies have demonstrated that 30 to 45% of patient s who died of seminoma initially diagnosed harbored nonseminomatous metasta ses and had an elevated serum AFP. We analyzed AFP expression by immunohist ochemistry and by nested reverse transcription-polymerase chain reaction (R T-PCR) in 10 seminomas, 3 embryonal carcinomas, and 1 immature teratoma, di agnosed by traditional clinical methods. Positive immunohistochemical stain ing was observed in all embryonal carcinomas and in the teratoma but not in the seminomas. AFP mRNA, however, was found in 6 of 10 seminomas, in all e mbryonal carcinomas, and in the teratoma. The nucleotide sequence of PCR pr oducts was identical with that of the AFP gene. We conclude that the analys is of AFP gene expression by nested RT-PCR would be useful for detecting mi nute quantities of nonseminomatous germ cell elements in classic seminoma. Moreover, the existence of AFP mRNA suggests the possibility that seminoma cells can differentiate into nonseminomatous germ cells.