High levels of cytokeratin 19 fragments but no evidence of cytokeratins 1,2, 10/11, 14 or filaggrin in the serum of squamous cell lung carcinoma patients

The CYFRA 21-1 assay detects circulating fragments of cytokeratin 19, which is a sensitive marker for the diagnosis of lung cancers, particularly squa mous cell carcinomas and adenocarcinomas. Epidermis-type proteins, such as cytokeratins 1, 2, 10/11 and 14 or filaggrin, are also expressed in squamou s cell carcinomas. These could also be pertinent tumor markers, ideally as sensitive as CYFRA 21-1 and more specific for squamous cell lung cancer. To verify this hypothesis, using monoclonal antibodies produced in our labora tory, we developed immunoassays specific for these proteins. After optimiza tion, the immunoassays were evaluated in sera from 91 controls and 138 pati ents with squamous cell lung cancer and compared to conventional tumor mark ers (CEA, SCC Ag and CYFRA 21-1). Less than 14% of the sera were above the lower limit of detection of the cytokeratin- and filaggrin-specific immunoa ssays. Moreover, part of these positive sera were induced by the presence o f interfering heterophilic antibodies in sera. Thus, in patients with squam ous cell lung cancer, we confirmed the high diagnostic sensitivity of CYFRA 21-1 (55.6%) but were unable to detect significant levels of epidermis-typ e cytokeratins or filaggrin. Copyright (C) 2000 S. Karger AG, Basel.