Among 20 known cytokeratins, cytokeratin fragment 19 is a 40 kD acidic molecule whose distibution is restricted to simple or pseudo-stratified epitelia, such as the epithelial layer of the bronchial tree. An immunoradiometric assay, CYFRA 21-1, was used to detect a fragment of cytokeratin 19 in the serum of 90 subjects and compared with serum levels of CEA, NSE and TPA. Sixty-seven consecutive patients with lung cancer and 23 healthy subjects were tested. Cut-off values for tumor markers were considered as the 95% of specificity versus controls. There were 32 adenocarcinomas, 29 squamous carcinomas and 6 other tumors. Increased serum levels of CYFRA 21-1 were found in lung cancer patients compared to controls [1.6 (0.2-3.2) versus 0.5 (0.2-1.8): p<0.001]. In our study TPA was more sensitive than CYFRA 21-1: 49% versus 40%; when we combined both markers the sensitivity increased to 63%. Significant difference in values were found before and after surgery in serum levels of 34 operated patients: p<0.01. We found higher levels of soluble cytokeratin 19 in lung cancer patients and in the adenocarcinoma subgroup. This study does not support the exclusive use of soluble cytokeratin 19 as a specific marker of lung cancer and not only in squamous carcinoma subgroup. This suggested that diagnostic and prognostic sensitivity increase when CYFRA 21-1 and TPA or other markers are combined.

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