Spindle cell squamous carcinoma of the lung. Immunocytochemical and ultrastructural study of a case.

A case of squamous cell carcinoma of the lung showing extensive spindle transformation is presented. On light microscopy, the tumour showed sheets and fascicles of elongated fusiform cells resulting in a growth pattern which closely resembled a sarcoma. Immunocytochemistry using tissue-specific antibodies against intermediate filaments demonstrated exclusive labelling of the tumour cells with prekeratin antibodies. Electron microscopy showed well-formed intercellular junctions and thick bundles of tonofilaments within the cytoplasm of the cells further confirming the squamous epithelial nature of the neoplasm. The findings in the present case point to the existence of a non-metaplastic spindle cell variant of squamous carcinoma of the lung. The possible mechanisms which may account for the spindle shape of the cells are reviewed.