Expression of a neural type of intermediate filament as a distinguishing feature between oat cell carcinoma and other lung cancers.

Expression of intermediate filaments was studied immunohistologically in oat-cell (6 cases), epidermoid (9 cases), adeno- (7 cases), large-cell anaplastic (3 cases), and bronchioalveolar carcinoma (3 cases), of lung. Affinity-purified antibodies against epithelial (anti-keratin), neural (anti-neurofilament), muscle (anti-desmin) and mesenchymal (anti-vimentin) intermediate filaments were used. In indirect immunofluorescence microscopy of oat-cell carcinomas a positive cytoplasmic fluorescence was seen only with antibodies against neural intermediate filaments, neurofilaments, while no staining of the tumor cells was observed with antibodies against other types of intermediate filaments. On the other hand, all the epidermoid, adeno, anaplastic, and bronchioalveolar carcinomas showed constantly a strong reaction with anti-keratin antibodies in a varying number of cells but no decoration with anti-neurofilament antibodies. The results show that expression of neural intermediate filaments is a major distinguishing feature between oat-cell carcinomas and other lung cancers and suggest that anti-neurofilament antibodies can be used as a diagnostic aid in the surgical pathologic study of pulmonary neoplasms.