[Stromal bone formation by lung adenocarcinoma]

We report a case of lung adenocarcinoma with stromal bone formation. A 73-year-old woman was incidentally found to have a coin lesion in the left lower lung field on a chest roentgenogram and computed tomography showed a nodular lesion containing a few coarse high density areas in the left lower lobe. Since transbronchial cytology revealed adenocarcinoma, left lower lobectomy was performed. Histologically, the tumor was a papillary-tubular adenocarcinoma, and fragments of osseous tissue were found within abundant fibrous stroma. Bone formation in primary lung adenocarcinoma is a very rare condition, and only 7 other cases have been reported in the literature.