Primary osteosarcoma of the lung. A reappraisal following immunohistologic study

Five neoplasms were initially believed to represent primary osteosarcomas of the lung. Of the five cases, two were reinterpreted as carcinosarcomas based on the identification of epithelial elements on further histologic sectioning and immunohistologic study in one and on immunohistologic study alone in the second. The differential diagnosis of carcinosarcoma should be considered for any lesion believed to represent a primary sarcoma of the lung, and in some cases carcinomatous elements may only be demonstrable by immunohistologic means.