Histochemical and ultrastructural features of an unusual pulmonary carcinosarcoma.

An autopsy case is presented in which a pulmonary carcinosarcoma filled the left chest of a 61 year old man. The extensive pleural involvement that this neoplasm exhibited has not been reported previously. By light microscopy the neoplasm initially was considered a mesothelioma because of the pattern of glands and undifferentiated sarcomatous stroma. However, by electron microscopy the sarcomatous component was found to show rhabdomyoblastic differentiation. Neither histochemical stains nor electron microscopy supported a mesothelial origin for the glandular component. Differential diagnostic considerations of pleuropulmonary neoplasms showing rhabdomyosarcomatous differentiation are discussed. This case illustrates the importance of detailed study in order to characterize and properly classify these neoplasms.