The expression of five different claudins in invasive breast carcinomas: comparison of pT1pN1 and pT1pN0 tumors.

The evaluation of the role of claudins (CLDNs) in breast carcinogenesis has recently begun. We investigated the expression of CLDNs 1, 2, 3, 4, and 7 in pT1pN0 and pT1pN1 invasive ductal breast carcinomas. Tissue arrays of 30-30 pT1pN0 and pT1pN1 invasive ductal breast carcinomas of different grades were constructed, and the expression of CLDN 1, 2, 3, 4, and 7 proteins was analyzed using standard and immunofluorescent immunohistochemistry. The results were evaluated by light and confocal microscopy. Regarding CLDN 1, 4, and 7 expressions, differences were noted between normal and tumor cells and also between tumors of different grades, while no remarkable differences were noted between pT1pN0 and pT1pN1 tumors. CLDNs 1 and 7 were found to be downregulated in tumor cells compared to the normal epithelium, while CLDN 4 expression was decreased in grade 1 tumors. CLDN 7 protein was abundant in normal epithelia, and the staining decreased in grade 3 tumors. There were no differences between normal and neoplastic cells regarding CLDN 2 and 3 expressions. As a preliminary result, our observations suggest that the analyzed CLDNs do not promote tumor metastasis. On the basis of our findings, it seems that CLDN 1, CLDN 4, and CLDN 7 may rather have an important role in tumorigenesis or in cell-to-cell adhesion.