[Case of pulmonary adenocarcinoma with co-existing pulmonary actinomycosis in one region of the lung].

A 64-year-old man presented with chronic cough. Chest CT revealed a nodular shadow with cavitation in the right S6. Seven months after his first examination, the nodular shadow had gradually increased, so flexible fiberoptic bronchoscopy was performed. The results of bronchial brushing and aspiration cytology were negative, however, gram-stained smear of the bronchial aspirate revealed many gram-positive rods with branching filamentous hyphae and culture of the bronchial aspirate was positive for the Actinomyces species. On a diagnosis of pulmonary actinomycosis, 1500 mg of oral amoxicillin was initiated. After 4 months of treatment, the right S6 nodule size was unchanged and the level of CYFRA in serum was elevated. Therefore, video-assisted thoracic surgery (VATS) was performed. A histological examination of the resected tumor showed papillary and acinar adenocarcinoma. The common radiological features in patients with pulmonary actinomycosis are nodules, mass formation and cavitation. Pulmonary actinomycosis requires differentiation from lung cancer. Although lung cancer with coexisting pulmonary actinomycosis is rare, clinicians should take into consideration the fact that lung cancer and pulmonary actinomycosis can co-exist in the same patient.