Fine-needle aspiration cytology of pulmonary carcinosarcoma with immunocytochemical and ultrastructural observations.

The cytologic, immunocytochemical, and ultrastructural features of a pulmonary carcinosarcoma diagnosed by fine-needle aspiration biopsy are presented. Both malignant epithelial groups and bizarre spindle-shaped cells arranged in loose groups, microtissue fragments and in a dissociate fashion showed dual immunoperoxidase staining with cytokeratins and vimentin. Although the immunocytochemical staining pattern is typical of this neoplasm, it does not allow differentiation in all cases from the more common primary large-cell undifferentiated carcinoma, which can also show dual staining for cytokeratin and vimentin. However, the presence of poorly differentiated epithelial groupings associated with a malignant mesenchymal component set in a myxoid stroma should suggest the correct diagnosis. Cytologically, differentiating carcinosarcoma, a poorly differentiated malignancy showing dual staining for cytokeratin and vimentin, from a large-cell carcinoma is important, since the former may pursue a more indolent clinical course.