Detection of epithelial- and neural type of intermediate filament proteins in human lung tumors

Five different types of lung cancers, i.e. squamous cell carcinomas, adenocarcinomas, small cell lung carcinomas, carcinoids and adenoid cystic carcinomas were examined for their intermediate filament constituents, with special emphasis on the different cytokeratin polypeptides and neurofilament proteins. Polyclonal as well as monoclonal antibodies to these proteins were used in immunocytochemical techniques applied to both tumor frozen sections and paraffin sections. Squamous cell carcinomas and adenocarcinomas could be shown to contain cytokeratins, which could be detected in both frozen sections and paraffin sections. Also small cell lung carcinoma (SCLC) and carcinoid lung tumors showed a positive staining reaction with polyclonal and monoclonal (cyto)keratin antibodies, but were negative with neurofilament antibodies, with the exception of one case of lung carcinoid, which co-expressed neurofilaments and cytokeratins. We have used antibodies to cytokeratin polypeptides, to neurofilament proteins and to a neuroendocrine related membrane antigen (MOC-1) to further subclassify heterogeneously composed squamous cell carcinomas. Using a monoclonal antibody to cytokeratin 18, normally present in glandular tissues and adenocarcinomas, we observed that more than 90% of the squamous cell carcinomas examined can be stained with this antibody. The percentage of tumor cells, however, positive for cytokeratin 18 varies between 1 and 100%. In these same tumors a monoclonal antibody to skin keratins, which is known to react specifically with keratinizing cells, also stained variable numbers of tumor cells. This finding confirms the presence of (keratinizing) squamous cell carcinoma elements in these tumors. Our data show that most lung tumors, heretofore considered pure squamous cell carcinomas, should be considered biologically adenosquamous carcinomas. Also areas positive with MOC-1 were found in these tumors, suggesting the presence of squamous cell carcinomas with neuroendocrine differentiation. Furthermore, in some poorly differentiated squamous cell carcinomas areas with neurofilament positive cells were detected, suggesting a neural differentiation within these neoplasms. Adenoid cystic carcinomas are shown to co-express cytokeratins and vimentin in the tumor cells. This phenomenon can be used to identify such tumors and to distinguish them from other lung tumors.