Expression of claudins 1, 2, 3, 4, 5 and 7 in various types of tumours

Aims : Claudins are adhesion molecules present in tight junctions. To evaluate their usefulness as differentiation markers claudins 1, 2, 3, 4, 5 and 7 were studied in 116 epithelial and 92 non‐epithelial tumours. Methods and results : Immunoreactivity for all claudins could be seen in different carcinomas. There were, however, tumour type‐specific differences in their expression. Lower expression of claudin 2 was seen in breast and prostatic carcinomas, while hepatocellular and renal carcinomas expressed lower levels of claudins 4 and 5. In contrast to epithelial tumours, lymphomas did not express claudins and most soft tissue tumours and naevocytic lesions were negative or showed weaker, mainly cytoplasmic positivity for some claudins. Of non‐epithelial tumours, claudin 5 was found only in angiosarcomas and benign vascular tumours, which also showed reactivity for claudins 2, 3 and 7, but was not expressed in any other soft tissue lesions or lymphomas. Conclusions : The results show that claudins 1, 2, 3, 4, 5 and 7 can be used as markers for epithelial differentiation and to distinguish epithelial neoplasms from lymphomas and selectively also from soft tissue and naevocytic lesions. Since these claudins show type‐specific differential expression in epithelial tumours, they may also be of some value in distinguishing different epithelial tumours from each other. Additionally, claudin 5 shows promise as a marker for endothelial lesions compared with other soft tissue lesions.