Distinctive immunofluorescent labeling of epithelial and mesenchymal elements of carcinosarcoma with antibodies specific for different intermediate filaments.

A carcinosarcoma of the lung, as well as the paratracheal lymph nodes from the same patient, were subjected to immunofluorescent labeling with antibodies to tissue-specific intermediate-filament subunits, including desmin, vimentin, and prekeratin. Within the tumor mass two distinct populations of malignant cells were found: prekeratin-positive cells, corresponding to the carcinomatous component of the tumor, and vimentin-positive cells, corresponding to the sarcomatous elements. Tumor cells were also detected in lymph node metastases in which only the prekeratin-containing carcinoma cells were found. In view of the strict specificity of antivimentin and anti-prekeratin for cells of mesenchymal or epithelial origin, respectively, it is proposed that the two components of the carcinosarcoma are derived from distinct cell types and are not morphologic variants of the same tumor.