Monoclonal antibody 43-9F: an immunohistochemical marker of embryonal carcinoma of the testis.

Discrimination between different types of germ cell tumours may be difficult in routine histological preparations. Additionally, none of the established immunohistochemical markers is completely reliable in diagnosis of embryonal carcinoma. A pilot study indicated that monoclonal antibody 43-9F--a marker of carcinoma-in-situ germ cells--may also react with embryonal carcinoma of the testis. In order to elucidate the applicability of 43-9F in diagnosis of embryonal carcinoma, 42 consecutive testicular germ cell tumours were tested immunohistochemically. Among the 42 tumours, 23 were seminomas and 19 were non-seminomas with seminomatous components in seven of them. Embryonal carcinomas were found in 15 tumours, two being of pure type and the remaining 13 a part of mixed tumours. Additionally, the material included 11 teratomas, nine yolk sac tumours and one choriocarcinoma. Immunohistochemical stainings were performed with 43-9F and additionally with antibodies against placental-like alkaline phosphatase, cytokeratins, alpha-foetoprotein and human chorionic gonadotropin. Using 43-9F a strong colour reaction was found in 13 of the embryonal carcinomas, whereas the reaction was moderate in the remaining two cases. A weak positive reaction was found in six seminomas and the remaining 24 did not react at all. 43-9F exhibited a positive reaction in four of 11 teratomas. The reactivity was generally weak with some focal areas with strong staining. In five cases the yolk sac tumour elements did not stain with this monoclonal antibody. The reaction was weak in three cases and in only one case was the staining intensity scored as moderate. Finally, no reaction was found in the choriocarcinoma element. Compared to the other antibodies tested, including the antibody against cytokeratins, in embryonal carcinoma immunohistochemical staining with 43-9F was more specific, stronger and more constantly expressed. The monoclonal antibody 43-9F may be of value in histological diagnosis of germ cell tumours. Additionally, the study confirmed the pathogenetical link between pre-invasive carcinoma in situ and embryonal carcinoma.