ABSTRACT
An immunoperoxidase method has been used to demonstrate human chorionic gonadotrophin [HCG] in placental site trophoblastic tumours, hydatiform moles, and choriocarcinomas. In addition to cytotrophoblast, and syncytiotrophoblast, a third form of trophoblast designated intermediate trophoblast is present during pregnancy and in trophoblastic disease. Intermediate trophoblast has distinctive immunocytochemical features that distinguish it from cytotrophoblast and syncytiotrophoblast. The localization of HCG in both intermediate trophoblast and syncytiotrophblast varies with the type of trophoblastic neoplasm, and from one specimen to another within each category of tumour. Syncytiotrophoblast may contain HCG in large amount, whereas intermediate trophoblast contains HCG focally. Cytotrophoblast is devoid of HCG except in choriocarcinoms, which may show focal weak staining for HCG, Immunoperoxidase identification of HCG has proved helpful in clarifying the histogensis of trophoblastic neoplasms and may also be of value in establishing their diagnosis and in determining their prognosis