Primary lung adenocarcinoma with heterotopic bone formation.

A 46-year-old man was referred to our hospital for the treatment of lung cancer. Computed tomography showed a well-defined tumor mass that was 50×45 mm in size and contained a trabecular pattern of calcification. Since he was diagnosed as having a primary lung adenocarcinoma (clinical stage IB), a left upper lobectomy with mediastinal lymph node dissection was performed. Histologically, the tumor was a poorly differentiated adenocarcinoma with rich fibrous stroma, in which there were island-shaped bone formation lesions. An immunohistochemical examination showed the expression of bone morphogenic protein-2 within tumor cells, which induce and stimulate bone formation. This finding may elucidate a possible mechanism of heterotopic bone formation.