[The evaluation of the newly produced assay kit for the cytokeratin fragment, "ball ELSA CYFRA21-1"].

We evaluated the newly produced tumor marker assay kit, "Ball ELSA CYFRA21-1", which detects cytokeratin 19 fragment in the sera of patients with malignancies, especially lung cancers. The assay procedure is simple based on the one-step radioimmunometric assay method. The measured values depend somewhat on incubation temperature and time. Reproducibility and recovery were good. The minimum measurable level was 1 ng/ml. The dilution test was satisfactory. The CYFRA21-1 levels were gradually decreased by repeated freezing and thawing and after seven such exercises its activity dropped to about 70% of that of first assay. The presence of CYFRA21-1 antigen was strongly correlated with TPA antigen and, although some discrepancies could be observed in clinical samples, CYFRA21-1 activity was completely absorbed by anti-TPA antibody-coated beads in one sample. CYFRA21-1 levels of 44 normal controls were below 1.0 ng/ml. Assuming a cut-off value of 2.0 mg/ml, 32.7% of all cases with benign disease had values greater than 2.0 ng/ml. This fell to 21.4% on exclusion of cases of interstitial pulmonary disease. Those with malignant diseases had high CYFRA21-1 levels whether associated with lung cancer or not. The most high positive ratios were observed in squamous cell lung cancer, small cell lung cancer, and uterine cervical cancer. In conclusion, CYFRA21-1 may be a good tumor marker comparable to TPA not only for lung cancer but also other malignancies as well. High false positives for lung cancer, however, were observed in other pulmonary diseases.