Diagnostic utility of expression of claudins in non-small cell lung cancer: Different expression profiles in squamous cell carcinomas and adenocarcinomas

The claudins, members of a large family of adherent junction proteins, regulate the integrity and function of tight junctions. At present, at least 23 different claudins are known to exist in humans, and claudin gene expression is frequently altered in several human cancers. However, few studies have examined the expression of claudins in lung cancer. This study examined the expression of claudin-1, claudin-3, claudin-4, and claudin-5 proteins using immunohistochemical analysis in 14 normal lung tissue samples and 171 NSCLC samples. All of the claudin proteins examined were expressed in normal bronchial epithelial cells. In the normal peripheral parenchyma, only claudin-5 strongly stained most of the pneumocytes. Claudin-1 expression was stronger in squamous cell carcinomas than in adenocarcinomas, whereas claudin-4 and claudin-5 expression was stronger in adenocarcinomas. Clinically, expression of claudin proteins was not found to be associated with patient survival. These data suggest that the disruption of tight junction protein might be involved in the development of these tumors. Immunohistochemical evaluation of the different expression patterns of claudins in NSCLC suggests that claudin-4, in addition to 1 and 5, might be a useful differential diagnostic marker in Korean people.