Assessment of serum CYFRA 21-1 in lung cancer

Cytokeratins are the intermediate filaments of the cytoskeletal protein located in normal epithelia, tumor, and cultured cells. Recently, a fragment of cytokeratin subunit 19, referred to as CYFRA 21-1, detected in the serum of patients with nonsmall cell lung cancer, has been reported as a new tumor marker. This article reports the results of a study of serum fragment CYFRA 21-1, measured by immunoradiometric assay, as a marker of lung cancer.

One hundred fourteen patients with primary lung cancer, 6 patients with malignant solid tumor, 116 patients with a variety of benign diseases, and 29 normal individuals were entered into the study. Serum CYFRA 21-1 levels were obtained by means of immunoradiometric assay using the CYFRA 21-1 EIA (enzyme immunoassay) kit. In addition, we studied other tumor markers, including carcinoembryonic antigen (CEA), squamous cell carcinoma antigen (SCC), and neuron specific enolase (NSE), as a means of lung cancer diagnosis.

The diagnostic accuracy and sensitivity of serum CYFRA 21-1 for the detection of lung cancer were highest among the four markers. The serum CYFRA 21-1 levels were most highly elevated in lung carcinoma patients (in particular UICC Stage IV patients) across different histologic types and attained 85.1% sensitivity when using a threshold of 3.5 ng/mL. The diagnostic sensitivity for detecting lung carcinoma was substantially enhanced by means of combined assays of CYFRA 21-1 with CEA overall for lung cancer, with SCC for squamous cell carcinoma, and with CEA for adenocarcinoma.

These findings suggest that serum assays of CYFRA 21-1 are clinically useful for the diagnosis of lung carcinoma.