The differential diagnosis of choriocarcinoma and placental site tumour

Abstract

Choriocarcinoma (CH), the first human neoplasm to be monitored by a tumour marker and cured by chemotherapy, presents unique diagnostic problems because of its rarity and because criteria used to define malignancy in other neoplasms, such as vascular invasion, cellular pleomorphism, mitoses and even metastases, are intrinsic features of normal trophoblast. In no other neoplasm is the context in which trophoblast is found as important or more important than its appearance. It follows that clinico-pathological correlation is essential. Finding abundant pleomorphic trophoblast after a complete mole (CM), often means persistence of the mole with no chorionic willi in the sample, but finding abundant pleomorphic trophoblast after a normal term pregnancy is almost certainly due to CH or to a new pregnancy. Placental site trophoblastic tumour (PSTT) is a chenoresistant form of trophoblastic tumour with less tendency for vascular invasion or metastases but, in most cases, only curable if it can be eradicated by surgery. CH and PSTT look different and behave in different ways, but in some cases they merge into each other. The main diagnostic problems encountered are: firstly, the differentiation of CH and PSTT from the abundant trophoblast, usually seen in early gestation; secondly, the differentiation of CH and PSTT from persistent trophoblast after a molar or non molar pregnancy; thirdly, the differentiation between CH with a predominantly cytotrophoblastic component and PSTT; and fourthly, the differentiation between CH, PSTT and trophoblastic metaplasia in non-gestational carcinomas.