Clinical usefulness of serum cytokeratin 19 fragment as a tumor marker for lung cancer.

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 CYFRA level determination in the diagnosis and monitoring of lung cancer. Serum levels of CYFRA were measured by a 2-step sandwich ELISA method. When the cut-off value was defined as 3.5 ng/ml, which was associated with a specificity of 95% for benign lung diseases, CYFRA had a high sensitivity (53%) in all patients with lung cancer. Both the serum level of CYFRA and its sensitivity increased significantly with the increase in clinical stage. A comparison of areas under receiver operating characteristic curves showed that CYFRA had the most power of discrimination in the diagnosis of lung cancer among markers 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 CYFRA levels during therapy and clinical responses for 18 patients who underwent chemotherapy and/or radiotherapy. Our findings suggest that CYFRA may be a marker of choice for screening and monitoring of lung cancer, particularly squamous cell carcinoma.