Flow cytometry in persistent trophoblastic disease.

Abstract

About ten per cent of patients with a complete hydatidiform mole develop persistent trophoblastic disease (PTD) (Womack and Elston, 1985) including invasive mole and choriocarcinoma, and a complete hydatidiform mole is the preceding gestation in at least 50 per cent of choriocarcinomas (Elston, 1981). Other choriocarcinomas of gestational origin follow normal pregnancies and spontaneous abortions. The malignant potential of the complete mole has been well documented, but in addition there are several reports in the literature of PTD and one probable case of fatal metastatic choriocarcinoma following the evacuation of partial mole (Szulman et al, 1981; Stone and Bagshawe, 1976; Looi and Sivanersaratnam, 1981). It is therefore recommended that the clinical management of partial mole be no different from that of complete mole, and that patients with either type of disease be followed up with regular hCG assays (Womack and Elston, 1985). The diagnosis of a complete mole is usually straightforward provided that account is taken of clinical data and both macroscopic and microscopic features of the evacuated mole (Elston, 1984). The diagnosis of a partial mole, however, may be much more difficult (Messerli et al, 1987) especially in its differentiation from a hydropic abortion (unpublished observations). There is a risk that a partial mole may be overlooked and the patient lost to hCG follow-up; this could have unfortunate consequences for those patients with partial mole who may have a significant risk of PTD. In a previous study, we found that flow cytometry was a valuable tool in the diagnosis of molar pregnancies, especially when histological appearances were equivocal (Hemming et al, 1987). Furthermore we analysed seven cases of PTD and showed these to be diploid with cell turnovers (hyperdiploid fractions) characteristic of diploid complete mole. These findings prompted us to investigate a larger series of PTD. Our aim was to identify patients with molar pregnancies at risk of developing PTD and to clarify the risk of PTD for each subtype of hydatidiform mole. We also analysed four cases of choriocarcinoma in order to determine the flow cytometric characteristics of these malignant tumours.