Lung cancer complicated with IgG4-related disease of the lung.

Few have reported a concomitant malignant neoplasm with immunoglobulin G4 (IgG4)-related diseases. We describe a case of lung cancer and gastric cancer accompanied with IgG4-related disease. A 78-year-old man had an area of ground-glass opacity with central collapse in right upper lobe and a gastric cancer. The patient underwent a right upper lobectomy following a gastrectomy for the gastric cancer. Histological examination of the resected lung specimen revealed a lepidic pattern of an adenocarcinoma and a large amount of plasmacyte infiltration around the tumor. In immunohistochemical findings, the plasmacytes were stained for IgG4. Therefore, the lung tumor was considered to have associated with IgG4-related interstitial lesions.