Leydig cell tumor with lung metastasis diagnosed by lung biopsy.

Leydig cell tumors are very rare and account for only 3% of testicular tumors and are generally benign. Only less than 0.2% of all testicular cancers were evidenced by metastatic spread. We report a 34-year-old man visited hospital because of coughing sputum mixed with blood. His chest CT showed bilateral patch clouding opacity. He was suspected with allergic alveolitis and treated with methylprednisolone. However, his symptoms and general condition deteriorated, and he visited our hospital. He had no abnormal findings on physical examination. A chest radiograph showed pneumonia in whole lung and CT showed multiple nodules and diffused ground glass opacities in both lung fields. Lung biopsy confirmed a diagnosis of Leydig cell tumor with lung metastasis. The diagnosis is based on the histopathology and immunohistochemistry.