Expression of cytokeratin and neuron-specific enolase in small cell carcinomas of the lung.

Using a polyclonal antibody against human epidermal keratins and a monoclonal antibody against cytokeratins characteristic of simple epithelia, and the Avidin-Biotin system of immunohistochemistry, we have demonstrated cytokeratin expression in 46% and in 60% of small cell carcinomas of the lung at autopsy respectively. The latter gave a diffuse stronger reaction product than the polyclonal antibody. The results suggest that there is a cytokeratin rich and a cytokeratin poor type of small cell carcinoma. Neuron-specific enolase immunohistochemistry was positive in 60% of the cases. Coexpression with cytokeratin was seen in ten cases (30%). The expression of cytokeratin and neuron-specific enolase in small cell carcinomas strongly suggests that they are of an epithelial origin, but are capable of neuroendocrine differentiation.