[A large nontuberculous mycobacterial granuloma mimicking lung cancer; report of a case].

A 45-year-old woman with no immunodeficiency or clinical symptoms presented to our hospital for treatment of an enlarging spherical lung tumor in 4.0-cm-diameter. Chest radiography 8 years ago had shown a 1.5-cm-diameter tumor. Chest computed tomography (CT) showed the solitary tumor, located in the right apical segment, to have an irregular margin without satellite lesions or cavitations. Mycobacterium avium complex (MAC) was cultured in tumor specimens incised during transbronchial biopsy. Right upper lobectomy was performed because of resistance to 6-month antituberculosis treatment. Pathological findings showed a MAC-infected granuloma with caseous necrosis. Postoperative course was uneventful and she had no recurrence 3 years after surgery. These findings suggest that nontuberculous mycobacterial granuloma can enlarge without clinical manifestations or any satellite lesions and cavitations, leading to a misdiagnosis of lung cancer.