Immunohistochemical localisation of alpha-fetoprotein (AFP) in germ cell tumours: evidence for AFP production by tissues different from endodermal sinus tumour.

20 germ cell tumours have been studied with respect to the presence of alpha-fetoprotein (AFP), using the peroxidase-antiperoxidase (PAP) technique. 6 out of 20 tumours contained elements of endodermal sinus tumour (EST) and were AFP positive. 16 tumours were diagnosed either as pure embryonal carcinomas (6) or as mixed germ cell tumours, containing elements of embryonal carcinoma (10). In 3 of these 16 tumours AFP was localised definitely in the embryonal carcinoma cells; in an additional 6, AFP was also detected but it could not be decided whether AFP was present in embryonal carcinoma cells or in EST cells during early differentiation. In 2 of 7 immature teratomas, AFP was shown to be present in cylindric epithelia. All seminomas (4) studied were AFP-negative. These results show that AFP, which occurs regularly in EST, may also be present in embryonal carcinomas as well as in immature teratomas. Thus, it seems that the immunohistochemical demonstration of AFP by the PAP technique is a suitable method of identifying late stages of embryonal carcinoma or early stages of endodermal sinus tumour during the process of differentiation.