Metastatic gestational choriocarcinoma. Unusual pathologic variant following therapy

: Two cases of metastatic gestational choriocarcinoma to the lungs have been encountered that presented unusual histologic patterns. Both lesions were solitary metastases that followed multiple courses of chemotherapy, and the patients had low serum beta-human chorionic gonadotropin (hCG) levels. Surgical excision appeared to be curative in both cases. Both neoplasms were characterized by a predominance of uniform but highly atypical mononucleate trophoblastic cells. These cells infiltrated pulmonary parenchyma, forming nests of tumor with central dense necrotic debris. Syncytiotrophoblastic cells (STB) were present but showed scant cytoplasm and little vacuolization. Hemorrhage was only focal. Immunohistochemistry revealed that some of the multinucleate STB and occasional mononucleate cells produced hCG, while human placental lactogen was focally produced in the tumors. By electron microscopy the STB were identified but lacked open lacunae lined by microvilli. Most mononucleate cells showed greater maturation evidenced by a more complex cytoplasm than is seen in typical cytotrophoblastic cells (CTB). The results suggest that these tumors are a distinctive subtype of choriocarcinoma composed largely of a form of trophoblastic cell with features intermediate between CTB and STB, yet different from the intermediate trophoblast of the placental site tumor. Identification of this morphologic variant of choriocarcinoma may have clinical utility as additional cases are studied.