A novel IRMA and ELISA for quantifying cytokeratin 8 and 18 fragments in the sera of healthy individuals and cancer patients.

Cytokeratins 8 and 18 are most frequently co-expressed in simple epithelia and carcinomas. Fragments of these cytokeratins are released into the systemic circulation where they can be quantified and utilized as tumour markers. The present paper reports on a solid-phase sandwich monoclonal immunoassay, considered "epithelial tissue-specific", which recognizes fragments of human cytokeratins 8 and 18 of different sizes (10-50 kD). The evaluated ELISA and IRMA assays exhibited a detection limit of 0.1 microgram 1-1 and characteristically demonstrated a within-assay coefficient of variation (CV) of 1-4% and a between-assay CV of 3-5%. The long-term (300 days) repeatability of lyophilized samples tested in the assay was estimated to have a less than 10% CV. Of apparently healthy individuals, 95% were found to have serum concentrations of less than 0.95 micrograms 1-1. A highly significant difference was found between apparently healthy individuals and pancreatic cancer patients. Patients with metastatic disease showed a sensitivity of 93% and those with local disease 83%, at 95% specificity. This TPAcyk assay revealed good correlation (0.98) with the TPS assay detecting the specific M3 epitope of the tissue polypeptide antigen. The correlation with the long established polyclonal assay of tissue polypeptide antigen (TPA) was estimated to be 0.9.