Lung osteoma--a new benign lung lesion.

Extraskeletal osteomas have not been described in the lung. Tumors with osseous elements can be found, such as hamartoma and amyloid tumor, and reactive lesions such as osseous metaplasia. A 39-year-old male patient was treated for multiple myeloma and got a bone marrow transplantation 2 years and a few months before he presented with a solitary well-circumscribed tumor in the right middle lobe. The patient underwent surgical resection. The tumor presented with a fibrous capsule and consisted of mature bone trabecules. Within the tumor, fatty tissue was seen. There were small bone spicules interpreted as areas of new bone formation and appositional growth. No amyloid deposition, no immature epithelial tubules as in hamartomas, and no normal lung structure as in osseous metaplasia were seen. Within the osseous elements, a positive reaction was seen with antibodies for osteonectin, whereas the reaction for calcitonin was negative. To the best of our knowledge, this is the first case of an osteoma being reported in the lung looking like any other extraskeletal osteoma. This tumor might have been induced by circulating stem cells; however, due to autologous bona marrow transplantation, this cannot be proven.