Epithelioid trophoblastic tumor of the lung

Epithelioid trophoblastic tumor (ETT) is a rare type of gestational trophoblastic disease and only 25 cases have been reported so far. It was first proposed by Mazur and Kurman in 1994 as an unusual type of trophoblastic tumor that is distinct from placental site trophoblastic tumor and choriocarcinoma and has features resembling carcinoma. A case of ETT of the lung in a 38-year-old Japanese woman is reported. The patient had suffered from a hydatidiform mole at the age of 27 years, and had four normal deliveries at the ages of 24, 31, 35 and 37 years. Because no tumor lesions were detected in the uterus, the patient was suspected of having metastatic choriocarcinoma with multiple lesions in the lung accompanied by an elevated level of human chorionic gonadotropin (hCG). In order to make an exact diagnosis, a partial resection of metastatic foci in the lung was performed. Microscopically, the tumor showed hemorrhagic necrotic foci and was composed of mainly mononuclear tumor cells and some giant tumor cells resembling trophoblastic cells. Immunohistochemical examination showed that a few large cells were stained positively for hCG, and that other cells were positive for human placental lactogen, pregnancy-specific β1-glycoprotein, cytokeratin 7 and inhibin-α. In the ultrastructure, the tumor cells contained large nuclei and rich organella with desmosomes and well-formed filaments. The diagnosis of ETT was confirmed from the findings as described above.