Clinical Usefulness of CYFRA Assay in Diagnosing Lung Cancer: Measurement of Serum Cytokeratin Fragment

We evaluated the diagnostic usefulness of measurement of the soluble cytokeratin 19 fragment, a new tumor marker, in 391 patients with lung cancer and in 424 patients with benign lung diseases. Serum concentrations of cytokeratin 19 fragment were measured by a sandwich ELISA (CYFRA). The cut‐off value was defined as 3.5 ng/ml, which is associated with a specificity of 85% for benign lung diseases. CYFRA had a high sensitivity (57.5%) in all subjects with lung carcinoma, and had a higher sensitivity for squamous cell carcinoma (73.1%, n = 141) than squamous cell carcinoma‐related antigen (61.0%). CYFRA was associated with a relatively high sensitivity (42.1%) in early‐stage squamous cell carcinoma (stage I, based on the classification of the Japan Lung Cancer Society), but the CYFRA titer was higher in advanced squamous cell carcinoma than in early‐stage squamous cell carcinoma. Our findings suggest that CYFRA is potentially useful for diagnosis and monitoring of lung carcinoma, especially for squamous cell carcinoma.