Serum soluble cytokeratin 19 fragment (CYFRA)levels were measured in 251 patients with lung cancer and 139 patients with benign lung diseases to determine the clinical usefulness of CYFRAlevel determination in the diagnosis and monitoring of lung cancer. Serum levels of CYFRAwere measured by a 2-step sandwich ELISA method. Whenthe cut-off value was defined as 3.5 ng/ml, which was associated with a specificity of95% for benign lung diseases, CYFRAhad a high sensitivity (53%) in all patients with

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... lung cancer. Both the serum level of CYFRAand its sensitivity increased significantly with the increase in clinical stage. A comparison of areas under receiver operating characteristic curves showedthat CYFRA had the most power of discrimination in the diagnosis of lung cancer amongmarkers including carcinoembryonic antigen, squamous cell carcinoma antigen, carbohydrate antigen 19-9, and neuron-specific enolase. A good correlation was found between serial changes in serum CYFRAlevels during therapy and clinical responses for 18 patients who underwent chemotherapy and/or radiotherapy. Our findings suggest that CYFRAmay be a marker of choice for screening and monitoring of lung cancer, particularly squamous cell carcinoma. (Internal Medicine 35: 764-771, 1996)