Immunohistochemical localization of keratin-type proteins in epithelial neoplasms. Correlation with electron microscopic findings.

A rabbit antiserum prepared against human keratins isolated from calluses was applied to sections of 108 neoplasms using indirect immunofluorescence and immunoperoxidase technics. The vast majority of epithelial neoplasms were strongly positive for keratin-type proteins, even in the absence of obvious keratinization or squamous differentiation as revealed by light microscopy. This keratin-positivity was invariably correlated with the identification of intermediate-sized filaments arranged in loose or dense bundles in the cytoplasm of neoplastic epithelial cells. Keratin-negative neoplasms included nevi, malignant melanomas, carcinoid tumors, malignant lymphomas, and a variety of connective-tissue tumors. Immunologic identification of keratin-type proteins was particularly helpful in establishing the epithelial nature of "undifferentiated" malignant tumors, including oat cell carcinomas.