Villotrophoblastic pulmonary nodule with implantation site intermediate trophoblasts after induced abortion

We describe a case of villotrophoblastic pulmonary nodule with a hitherto unrecognized implantation site intermediate trophoblasts (ISITs) in an asymptomatic 19-year-old woman, who had an induced abortion 1 month before the discovery of a pulmonary nodule. This 8-mm-sized nodule was incidentally identified on chest computed tomography during routine postoperative follow-up for osteosarcoma, for which she was treated with surgery and chemotherapy 3 years previously. The nodule was located in the subpleural lung parenchyma and was composed histologically of a few chorionic villi and trophoblasts surrounded by fibrinoid materials, with individually scattered intermediate trophoblasts at the periphery of the nodule. The intermediate trophoblasts were strongly immunopositive for cytokeratin, human placental lactogen, and Mel-CAM (CD146), but immunonegative for human chorionic gonadotropin and p63, characteristic features of ISITs. Our case indicates that villotrophoblastic pulmonary emboli have the potential to implant after migration from their original sites through the invasive property of ISITs.