[Squamous cell carcinoma of unknown origin affecting mediastinal lymph nodes]

A 65-year-old woman was admitted to the hospital because of an abnormal shadow on a chest X-ray film. Chest CT scans showed enlargement of the right mediastinal lymph nodes. However, no primary lesion was detected despite thorough examination. Mediastinoscopic biopsy revealed that the tumor was a lymph-node metastatic lesion of a squamous cell carcinoma of unknown origin. A thoracotomy was done and the mass was completely resected. Radiotherapy was given after the operation. We have followed the patient for 1 year since the operation, but no primary lesion has yet been detected. Metastasis of cancer of unknown origin to hilar or mediastinal lymph nodes is extremely rare, and only 6 cases have been reported previously in the Japanese medical literature.