Resection for an Extremely Rare Pleomorphic Carcinoma of the Mediastinal Lymph Nodes of Unknown Primary: A Case Report.

Pleomorphic carcinoma of the mediastinal lymph nodes with an unknown primary site is extremely rare. A 68-year-old man was referred to our department after an enlarged lymph node in the right upper mediastinum was noted on computed tomography. An irregular nodule was also detected in the right upper lobe, showing no change compared with findings from 2 years earlier. FDG-PET (18F-fluorodeoxyglucose positron emission tomography) revealed strong uptake only in the mediastinal lymph nodes. EBUS-TBNA (Endobronchial ultrasound-guided transbronchial needle aspiration) of the lymph nodes revealed findings consistent with pleomorphic carcinoma. No other abnormalities were identified, and surgery was performed. As rapid pathology of the pulmonary nodule revealed no malignant findings, right upper mediastinal lymph node dissection was performed. The final pathological diagnosis was pleomorphic carcinoma. No malignant lesions were identified in the lungs. The patient has remained under strict observation, with no recurrence detected 1 year after surgery. Mediastinal lymph node carcinoma of unknown primary involving pleomorphic carcinoma, which carries a poor prognosis, needs strict follow-up owing to the risk of developing a future primary lung tumor.