Immunohistochemical analysis of tissue localization of cytokeratin 19 in lung cancer.

Cytokeratins (CK) are one of the main families of intermediate filaments which make up the cytoskeleton. CK19 is strongly expressed by normal simple bronchial and respiratory epithelium as well as by their malignant counterpart. Although CK19 is a part of the cytoskeleton, a soluble fragment of this polypeptide can be released and assayed in the blood as CYFRA 21-1, new sensitive and valuable marker of non small cell lung cancer. In some cases, however, discrepancies between the serum level of CYFRA 21-1 and presence of tumor and its histological type have been observed. We studied immunohistochemically tissue localization of CK19 in tumors and non invaded lung parenchyma in a series of 34 patients surgically treated due to lung cancer. CK 19 was detected in cancer cells as well as in non neoplastic epithelium covering bronchial tree and alveolar surfaces. We found a different expression of CK19 in different histological type of tumors. The most intensive expression revealed squamous cell carcinomas and adenocarcinomas. Small cell cancer revealed poor expression of CK19. In non invaded parts of the resected lungs we found the strong expression of CK19 in the cytoplasm of regenerative II type pneumocytes occurring in large quantity in the cases of interstitial lung fibrosis concomitant with some tumors. We suggest it may be a cause of unexpectedly elevated serum levels of CYFRA 19-21 in some not oncological patients or patients with small cell lung cancer.