[Pulmonary actinomycosis which was clinically suggested lung cancer; report of a case].

A 57-year-old man had been observed a mass-like shadow on a chest radiograph. One year later, chest computed tomography (CT) revealed the enlargement of the shadow. Positive finding of fluorodeoxyglucose-positron emission tomography (FDG-PET) suspected lung cancer, and lingular segmentectomy was performed. The pathological diagnosis was pulmonary actinomycosis. It is necessary to consider pulmonary actinomycosis is a differential diagnosis of lung cancer.