Gestational trophoblastic tumors: refining histologic diagnoses by using DNA flow and image cytometry.

During the past year much effort has been focused on defining the DNA content of gestational trophoblastic tumors. Flow cytometric and image analysis studies of molar pregnancies confirmed that the majority of partial hydatidiform moles were triploid, and, as expected, most complete hydatidiform moles were diploid or diploid/tetraploid. There were rather large intra- and interobserver variations in diagnosing hydropic abortuses and hydatidiform moles when the DNA content had not been assayed. Knowledge of the DNA content increased diagnostic accord. Interphase cytogenetic probes for specific chromosomes and analysis of dinucleotide repeat sequences (microsatellites) allowed determination of DNA ploidy and assignment of parental origin, respectively. Unusual cases of hydatidiform moles complicated by twin pregnancy were associated with delays in clinical diagnosis and increased rates of persistent and metastatic trophoblastic disease. Residual nodules of intermediate trophoblast, an unusual form of persistent trophoblastic disease, were relatively resistant to chemotherapy and required further surgical intervention. Though immunohistochemistry aids in distinguishing placental site trophoblastic tumor from choriocarcinoma, occasional tumors show overlapping immunohistochemical profiles.