[Microsatellite instability of bilateral breast carcinomas is not linked to down-regulated expression of DNA mismatch repair genes].

High-level microsatellite instability (MSI-H) occurs frequently in colorectal carcinomas and other tumors but exceptionally rarely in breast cancer. We showed earlier that every tenth metachronous contralateral tumor of bilateral breast cancer (biBC) followed the MSI pattern of development. That was attributed to down-regulation of expression of DNA mismatch repair (MMR) genes. Immunological status of MLH1, MSH2, MSH6 and PMS2 proteins was evaluated using 4 biBC tumor pairs which revealed different microsatellite stability patterns. MMR enzymes showed high expression in 3 microsatellite stable tumors and 3 MSI-L carcinomas. MSH6 expression was slightly lower in 1 out of 2 MSI-H tumors while MLH1, MSH2 and PMS2 patterns presented with high intensity of immunohistochemical staining. Hence, no relationship was established between biBC tumor microsatellite instability and low-level of MMR gene expression.