RER+ phenotype analysis in bilateral and unilateral breast carcinomas

RER+ (replication error) phenotype, also known as micro satellite instability (MSI), is caused by defects in DNA mismatch repair and is characteristic for a subset of colorectal carcinomas. RER+ does not occur in most of other human tumors. Our previous investigations, which were devoted to the studies of allelic imbalances, have revealed tumors with the features of RER+ phenotype in bilateral breast cancer (biBC) patients. This study was aimed to analyze this unexpected phenomena in detail. Standard panel of markers has revealed RER+ status in 6 out of 60 contralateral metachronous cancers obtained from biBC pairs; however, this abnormality did not occur in any of 50 first tumors from the metachronous cases. Analysis of 11 synchronous biBC (22 tumors) has identified only 1 carcinoma with MSI. None of 52 control unilateral ВС samples carried RER+ phenotype. Preferable occurrence of RER+ status in second metachronous carcinomas from biBC patients allows to suggest that the development of some contralateral breast neoplasms is triggered by the therapy for the first malignancy.