Trophoblastic pseudotumor of the uterus: clinicopathologic report with immunohistochemical and ultrastructural studies.

: The clinicopathologic feature of two cases of trophoblastic pseudotumor of the uterus are presented and compared with previously reported cases. In both cases, cancer was erroneously diagnosed. One patient, 27 years of age when first examined, presented metrorrhagia 10 months after a full-term delivery. The lesion was entirely removed by curettage and was no longer found in the hysterectomy specimen. The patient is alive and well more than 17 years after therapy. The other patient, 36 years of age at the initial examination, presented with metrorrhagia 23 months after a therapeutic abortion. The pseudotumor infiltrated the full thickness of the uterine wall. The patient is alive and well 3 years and 7 months after hysterectomy and radiation therapy. Histologically, the tumor consisted of large cells invading the myometrium in small clusters either as cords or as single cells. There were 2 mitoses/10 HPF of which some were atypical. Tumor cells containing chorionic gonadotropin (hCG) and a pregnancy-specific protein (SP1) were demonstrated immunohistochemically (alpha 2-PAG) and placental lactogen (hPL) in one case. Ultrastructurally, trophoblastic pseudotumor closely resembled cytotrophoblastic cells of the basal plate of the placenta.