Phenotypic similarities in bilateral breast cancer

Bilateral breast cancers that develop at similar times in an individual are likely to have been subjected to similar hormonal, environmental and genetic influences during tumourogenesis compared with metachronous tumours. As such, it is possible that tumour phenotype in synchronous bilateral breast cancer may display similar biological characteristics. The aim of this study was to identify phenotypic similarities between synchronous and metachronous bilateral breast cancers which may suggest a common origin. Thirty-three cases of synchronous and 46 cases of metachronous bilateral breast cancer that displayed similar tumour type were analysed for concordance in relation to various histological and immunohistochemical parameters. A higher level of concordance was demonstrated for synchronous cases with the highest level seen for oestrogen receptor. It is likely that this is related to similar tumourogenic pathways occurring at equivalent exposure times to various environmental and hormonal influences, although, in a proportion of cases, inherited genetic factors may play a role.