A dual expression of cytokeratin and neurofilaments in bronchial carcinoid cells.

Intermediate filaments (IF) are ubiquitous cytoplasmic structures which, by virtue of their cell- and tissue-type-specific characteristics, are widely used as markers of tissue derivation and as differential diagnostic aids in surgical pathology. In contradistinction to other IFs, vimentin filaments, characteristic of mesenchymal cells, may be co-expressed with other cell-type specific IFs--cytokeratin filaments, desmin filaments, glial filaments and neurofilaments--in some tumor cells, embryonic cells, and cells in vitro. In this study we describe a novel type of IF co-expression which does not involve vimentin-filaments, viz. the presence of both cytokeratin filaments and neurofilaments in human bronchial carcinoid tumor cells.