Are synchronous and metachronous bilateral breast cancers different? An immunohistochemical analysis aimed at intrinsic tumor phenotype.

Metachronous bilateral breast cancers, compared to synchronous bilateral breast cancers, are characterized by more aggressive phenotype, expressed by lower expression of estrogen receptor and stronger expression of cytokeratin 5/6 and vimentin; this does not, however, translate into differences in the distribution of intrinsic tumor phenotypes.