A Rare Combination of Dermatomyositis, Interstitial Pneumonia, and Lung Cancer in a Patient Treated with Immunosuppressive Therapy and Chemotherapy.

We herein report the rare case of co-occurring dermatomyositis (DM), interstitial pneumonia (IP), and lung cancer in a 59-year-old man. Computed tomography (CT) and positron emission tomography-CT showed the presence of a left lung tumor with IP, which was diagnosed as lung adenocarcinoma by a CT-guided tumor biopsy. We diagnosed DM based on the presence of myalgia, Gottron's papules, and anti-aminoacyl-tRNA synthetase antibody positivity in the patient. Co-occurrence of the above-mentioned three diseases is rare, and acute exacerbation of IP is a major cause of death in such cases. These patients can be treated with immunosuppressive therapy followed by chemotherapy.