A 13-year-old previously healthy girl presented with a 2-month history of persistent cough and intermittent fever and a 1-month history of left knee pain. She had been treated by her primary care physician with a course of oral and intravenous antibiotics for a rightsided pneumonia with transient improvement in symptoms. She had a history of fracture of the right ankle after mild trauma 4 months before presentation. Plain radiographs of the left knee revealed lytic lesions in the tibia and femur suspicious for osteomyelitis ( Fig 1A). She underwent curettage of the left tibial lesion, which demonstrated cords of bland basal cells with extensive squamous differentiation without malignant cytological features such as mitosis or apoptosis (Fig 2A). Pathology diagnosis was adamantinoma, and she was referred to our institution for further treatment.On presentation, the patient had a persistent cough, chest pain, and dyspnea. Air entry to the right lung was decreased. Chest x-ray showed a massive right-sided pleural effusion with a right hilar mass. The chest computed tomography (CT) scan showed a large heterogeneous right hilar mass measuring 8 cm ϫ 6.7 cm with extension to the right mainstem bronchus and right lower lobe lung collapse ( Fig 1B). Positron emission tomography (PET) -CT demonstrated avid fluoroudeoxyglucose (FDG) uptake in the region of the right hilum corresponding to the patient's primary lesion. Foci of increased uptake were also noted within several lymph node stations including right supraclavicular, anterior mediastinal, right mammary, and right subphrenic. Multifocal osseous metastatic disease was also noted within the vertebral bodies, right clavicle, humeri, femurs, tibias, and right talus ( Fig 3A). She underwent a video-assisted thoracoscopic surgical procedure, and multiple parietal pleural deposits were biopsied. Pathologic examination of pleural deposits showed an undifferentiated malignant tumor composed of cords and nests of small-to medium-sized cells with round to oval hyperchromatic nuclei, inconspicuous nucleoli, and scant eosinophilic cytoplasm. Numerous mitosis and apoptosis were seen ( Fig 2C). Immunohistochemistry staining demonstrated that the tumor cells from both left tibial lesion and pleural deposits were positive for cytokeratin AE1/AE3, focally positive for cytokeratin 7, and stained negative for CD45, CD99, S-100, alfa-fetoprotein, placental alkaline phosphatase, inhibin, desmin, CK20, CD117, chromogranin, Epstein-Barr virus-encoded RNA, terminal deoxynucleotidyl tranferase, CD3, synaptophysin, and calretinin. Tumor cells retained integrase interacter 1. Malignant cells were also found in the pleural fluid. Bone marrow biopsy showed involvement with a poorly differentiated epithelial tumor composed of nests and sheets of moderate to large cells with round vesicular nuclei, prominent nucleoli, and moderate amounts of eosinophilic cytoplasm. On the basis of her clinical presentation, we suspected nuclear protein in testis (NUT) midline carcinoma (NMC). The immunohistochemis...
