Tumor-to-tumor metastasis: lung cancer within a thymoma.

Tumor-to-tumor metastasis is a rare phenomenon. We present a rare case of an 83-year-old man with pulmonary squamous cell carcinoma and thymoma. Thymectomy and superior segmentectomy of the left lower lobe were successfully performed on the patient. This thymoma had a region of lung cancer. Metastasis from other tumors to thymoma is rare, and we found a report that described a pancreatic carcinoma metastasizing to thymoma. We report an extremely rare case of metastasis from lung cancer to a thymoma.