[A case of minimal size small cell carcinoma arising in abnormal branching bronchus with mycobacteriosis].

A 73-year-old male was referred to our hospital because of mycobacteriosis. Bronchoscopic examination revealed a depressed lesion with white pseudomembrane located between the orifice of B2 and B3 of the right upper lobe. From this pseudomembrane, Mycobacterium avium complex was cultured, and the patient was treated with antituberculous drugs. Four months later, a small white polypoid tumor was found at the same site, growing gradually. Biopsy specimens showed invasion of small cell carcinoma, so we started combination therapy with anti-cancer drugs and irradiation. With this therapy, the small polypoid tumor disappeared and we found the orifice of an abnormal branching bronchus between the orifice of B2 and B3. A case of minimal size small cell carcinoma arising at the orifice of an abnormal branching bronchus with mycobacteriosis was reported and case reports in Japan were reviewed.