The aim of this study was to evaluate the expression of the cell adhesion-related glycoproteins MUC-1, beta-catenin and E-cadherin in multicentric/multifocal breast cancer in comparison to unifocal disease in order to identify potential differences in the biology of these tumor types.

A retrospective analysis was performed on the expression of MUC1, beta-catenin and E-cadherin by immunohistochemistry on tumor tissues of a series of 112 breast cancer patients (total collective) treated in Munich between 2000 and 2002. By matched-pair analysis, 46 patients were entered into two comparable groups of 23 patients after categorizing them as having multicentric/multifocal or unifocal breast cancer. Matching criteria were tumor size, histology grade and lymph node status; based on these criteria, patients were distributed equally between the two groups (p = 1.000 each). Data were analyzed with the Kruskal-Wallis and the Mann--Whitney tests.

In the matched groups, we found a significantly down-regulated expression of E-cadherin in multicentric/multifocal breast cancer compared to unifocal disease (p = 0.024). The total collective showed even higher significance with a value of p < 0.0001. In contrast, no significant differences were observed in the expression of beta-catenin between multicentric/multifocal and unifocal tumors (p = 0.636 and p = 0.914, respectively). When comparing the expression of MUC1, E-cadherin and beta-catenin within the unifocal group, we found a significant positive correlation between E-cadherin and beta-catenin (p = 0.003). In the multicentric/multifocal group we observed, in contrast to the unifocal group, a significant decrease of MUC1 expression with increased grading (p = 0.027).

This study demonstrates that multicentric/multifocal and unifocal breast cancers with identical TNM-staging clearly differ in the expression level of E-cadherin. We suggest that the down-regulation of E-cadherin in multicentric/multifocal breast cancer is causally connected with the worse prognosis of this tumor type.