A new tumor marker for primary lung cancer was used to investigate the clinical significance of the cytokeratin 19 fragment (CYFRA 21-1). The serum level was measured in 52 patients with primary lung cancer, 38 patients with other pulmonary diseases, and 22 normal volunteers. These values were compared with values of other tumor markers (CEA, SCC, and NSE). When the cut-off value was established as 3.5 ng/ml, the positivity rate of primary lung cancer was 65%, and the false positivity rate of other pulmonary diseases was 8%. The positivity rate was the highest in squamous cell carcinoma (88.9%) and for adenocarcinoma it was 61.5%. Immunohistochemical staining revealed uniform, intense positivity within the cytoplasm of squamous cell carcinoma. The positivity rate of lung cancer, in clinical stages I, II, IIIA, IIIB, and IV, was 50%, 50%, 40%, 71%, and 72%, respectively. Even for early stage lung cancer, the rate was found to be high. From the ROC curve investigation results, CYFRA 21-1 is considered more sensitive and specific than CEA and SCC for all primary lung cancers and especially pulmonary squamous cell carcinomas.
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