[A case of squamous cell carcinoma of negative tumor shadow arising from pulmonary cyst]

We report a case of 53-year-old man who performed resection of infected cystic lung lesion seen from his childhood. Chest X-ray showed no remarkable change in the wall of the cyst, and tumor shadow was negative. As the chest cavity was severely adhesive, operation was ended in partial resection including the cyst. Pathological study revealed moderately differentiated squamous cell carcinoma replacing the entire cystic wall. Right upper lobectomy and dissection of lymph nodes were performed as second operation. Microscopically, carcinoma was limited in the wall of the cyst.