Biphasic Neoplasms of the Lung

Lung tumors with two lines of differentiation—epithelial and mesenchymal—are unusual and probably represent no more than 2% of all primary neoplasms of the lung. The two forms of pulmonary blastoma—monophasic and biphasic—represent a spectrum of differentiation. It is not uncommon to identify cases of monophasic pulmonary blastoma in which the tumor is associated with another malignancy not of mesenchymal origin, which renders the tumor biphasic on a different nature. Biphasic blastomas have more tendency to show hemorrhage and necrosis. Histologically, the epithelial component associated with biphasic blastomas is similar to that described in the monophasic variant of blastoma. However, the epithelial component in these tumors shows more cellular atypia and easily identifiable mitotic figures. Biphasic pulmonary blastomas also show the presence of a mesenchymal component in the form of muscle differentiation, cartilage, bone, or an unclassified spindle cell sarcoma. Carcinosarcoma also contains malignant epithelial and mesenchymal components. More often, definitive classification of these tumors is accomplished after complete surgical resection. Radiological imaging plays an important role in defining the details of these tumors, while immunohistochemistry plays a minor role and it is often used to determine specific types of sarcomatous elements.