[Basic and clinical studies on serum cytokeratin 19 fragment assay using Centocor CYFRA 21-1 kit in patients with lung cancer].

We evaluated the newly developed tumor marker assay kit, "Centocor CYFRA 21-1", an immunoradiometric assay (IRMA) kit for determining the serum cytokeratin 19 fragment using the sera of healthy subjects, patients with benign lung diseases and patients with lung cancer. The assay procedure is simple and based on the one-step IRMA system. There were no problems in reproducibility, dilution test and recovery test. The minimum detectable dose was 0.3 ng/ml. The antigen measured by this kit was immunologically cross-reactive with tissue polypeptide antigen (TPA) and CYFRA 21-1 concentration was closely correlated with TPA concentration in the patient's serum (r = 0.86, p < 0.01). The cut-off value of serum CYFRA 21-1 based on the assay results of this kit was calculated to be 1.6 ng/ml from the receiver operating characteristic curve. Three of 47 healthy subjects (6.4%) and 9 of 30 patients with benign lung diseases (30.0%) showed a concentration over the cut-off value. By contrast, serum CYFRA 21-1 concentration was elevated in 31 of 50 patients with lung cancer (62.0%), 11 of 13 squamous cell carcinoma patients (84.6%), 8 of 12 small cell carcinoma patients (66.7%), 4 of 7 large cell carcinoma patients (57.1%) and 8 of 18 adenocarcinoma patients (44.4%). In addition, the positive rate of serum CYFRA 21-1 in patients with lung cancer gradually increased with staging of the disease: 50.0% in stage I, 50.0% in stage II, 61.9% in stage III, and 76.9% in stage IV. Thus, our results suggested that the Centocor CYFRA 21-1 kit is a useful assay system for serum cytokeratin 19 fragment as a tumor marker in patients with lung cancer.