Ossification in lung metastases of primary colorectal adenocarcinomas

Ossification of lung tissue is a rare phenomenon, which can be found in association with carcinoid tumors of the lung or pulmonary blastomas. Very rarely, ossifications are observed in lung metastases of extrathoracal epithelial tumors. In these cases,the most probable primary focus is a colorectal adenocarcinoma. Our question was, whether ossifications in lung metastases are pathognomonic for colorectal adenocarcinomas and how they can be pathogenetically arranged. A total of 15 lung metastases with ossifications from 5 patients suffering from a colorectal adenocarcinoma were examined by means of immunohistochemistry. Thereby, we found an increased expression of bone morphogenetic protein (BMP) 2/4 and osteonectin in tumor cells,as well as an increased stromatogenous expression of collagen type III. We conclude that there is strong evidence of a primary colorectal adenocarcinoma when ossifications in lung metastases are found. In these cases, a common metastatic spread of tumor cells and tumor stroma seems to be probable.