Electron microscopy and immunohistochemistry studies of pulmonary carcinosarcomas expressing the transcription factor MEF-2 and showing significant cell-to-cell, cell-to-matrix, and epithelial-mesenchymal interactions.

Pulmonary carcinosarcomas are typified by the rare histological combination of mixed epithelial and mesenchymal malignant tumor cells. The author has experienced three cases of pulmonary carcinosarcomas with large mass formation. Case 1 was the combination of adenocarcinoma with focal squamous cell differentiation and chondrosarcoma. In case 2, adenocarcinoma was combined with rhabdomyosarcoma. Case 3 demonstrated a large cell neuroendocrine carcinoma and rhabdomyosarcoma. The immunohistochemical findings showed that many of the carcinoma cells in case 3 and some carcinoma cells in case 2 demonstrated neuroendocrine cell differentiation. The nuclei in all sarcoma cells stained definitively positive for the transcription factor MEF-2. Many of the lineage-specific transcription factors for lung development were not distributed in the tumor tissue. Ultrastructurally, in all three cases, cell-to-cell (forming cellular junctions), cell-to-matrix, and epithelial-mesenchymal interactions were seen. In the interface or boundary between the carcinoma cell nests and the matrix-embedded sarcoma cells, well-developed basal lamina and fibroblastic spindle cells were frequently seen, with an appearance similar to primitive fibroblastic or mesenchymal cells, extending thin cytoplasmic process around the carcinoma cell nests. In summary, carcinosarcoma cells interacted with each other and with their extracellular matrix, revealed MEF-2 in the sarcoma cells, and showed unique histological findings associated with a variety of phenotypic differentiation patterns very different from normal lung development. Copyright 2004 Springer-Verlag