AbstractsPartial mole is often associated with triploidy (69,XXY or 69,XXXY), the extra haploid set of chromosomes usually being paternal (Fig. 1). Although the benign nature of partial mole has been emphasized, cases of gestational trophoblastic tumor have been reported to follow. In this report, the authors present the pathological features of eight patients with partial mole (10 per cent of their total series of such patients) who had persistent trophoblastic tumor develop.The clinical histories, macroscopic descriptions of specimens, and slides of eight partial moles that resulted in persistent disease were reviewed and compared with 73 partial moles which did not persist.) After molar evacuation, all patients with molar pregnancies at the authors' institution are followed with weekly hCG assays until these have been normal for 3 consecutive weeks. Postmolar gestational trophoblastic tumor is diagnosed if the hCG level increases or levels off in a plateau for at least 3 consecutive weeksThe patients' ages ranged from 25 to 37 years (mean, 30.2 years). In each case, the initial clinical diagnosis was “missed abortion.” Preevacuation serum hCG levels, measured in four patients, varied from 440 to 70,000 lU/liter. Pelvic ultrasound examination was performed in each of the eight patients, and in seven cases, this study suggested missed abortion. One patient was considered to have a molar pregnancy. The time interval from initial molar evacuation to diagnosis of persistent gestational trophoblastic tumor ranged from 6 to 18 weeks. Pretreatment serum hCG levels ranged from 15 to 6,000 lU/liter. All eight patients achieved remission after single-agent chemotherapy (methotrexate and citrovorum factor).In five cases, molar vesicles 8 to 10 mm in diameter were observed in the original specimens. Intact autolyzed embryos were found in two specimens, and three others included autolyzed fetal fragments. Fetal membranes were noted in three cases. Scalloped villous outlines, stromal trophoblastic inclusions, and cavitated villi were present in all eight specimens. The degree of cavitation was more prominent than in villi of nonpersistent partial moles. The villi were focally covered by trophoblast, ranging from two to several layers in thickness, composed of both cytotrophoblast and syncytotrophoblast. The cytotrophoblast showed occasional mitotic activity. None of the initial specimens manifested unusual trophoblastic proliferation as compared with partial mole not followed by persistent disease.Villous vascular anomalies were noted in seven of eight cases. In four, dilated and anastomosing vascular channels were diffusely present (Fig. 2). Villous vascular anomalies were present in 17 per cent of nonpersistent partial moles. In most cases, intravascular nucleated red blood cells were present. Villous stroma of two partial moles with persistent tumor and 11 with no evidence of persistent disease contained bizarre stromal cells with large, round, or oval hyperchromatic nuclei and abundant eosinophilic cytoplasm. They manifested strong immunohistochemical staining for human placental lactogen and keratin (Fig. 3) and were negative for chorionic gonadotropin and lysozyme.