Bone formation by cancer metastases: case report and review of literature.

The formation of heterotopic bone tissue in malignant tumors or in their metastases is extremely rare. In a 60 years old male patient with bronchogenic carcinoma (adenocarcinoma) extensive bone formation was observed within multiple metastases in the skeletal muscles. On the basis of the microscopic findings, the mechanism of bone formation by malignant tumors is discussed. Obviously, proliferation of local mesenchymal tissue and differentiation of mesenchymal cells to osteoblasts is induced by the tumor cells.