Carcinosarcoma of the lung, a tumour which has a poor prognosis and is extremely rarely diagnosed preoperatively.

Out of about 2,000 patients operated on for lung cancer in the period from 1975 to 1990, four were found with the very rare condition carcinosarcoma. The diagnosis was verified by immunohistochemical investigation. The problems concerning this rare tumour are discussed with reference to four case descriptions and with consideration of the pertinent literature. On the one hand, they comprise the difficulty of making a correct histological diagnosis preoperatively, and on the other hand the poor prognosis, even in the NO stage.