Are bilateral breast cancers and breast cancers coexisting with ovarian cancer different from solitary tumors? A pair-matched immunohistochemical analysis aimed at intrinsic tumor phenotype.

Patients with bilateral breast cancer (BBC) and breast-ovarian cancer syndrome (BOCS) constitute populations potentially enriched for molecular defects involved in the pathomechanisms of these malignancies. The aim of our study was to compare tumor morphology and expression of estrogen and progesterone receptor, HER2, Ki67, cytokeratin 5/6, E-cadherin, vimentin and epidermal growth factor receptor in tissue microarrays from 199 tumors from BBC or BOCS patients and 199 age-matched solitary tumors. Compared to controls, BBC and BOCS considered jointly had lower incidence of DCIS, lower expression of PgR and HER2, and higher expression of Ki67 and vimentin. BOCS tumors were of higher grade, had lower expression of ER and PgR and higher expression of Ki67, CK5/6, vimentin and EGFR. BBC had less DCIS component, lower HER2 expression and higher Ki67 expression. Metachronous BBC (mBBC) had lower expression of ER, PgR and HER2, and higher expression of Ki67 and vimentin. Synchronous BBC (sBBC) had less DCIS component, higher expression of ER, and lower expression of CK5/6, EGFR and E-cadherin. BBC and breast cancers in BOCS differ in many aspects from solitary tumors. BBC are a heterogeneous group of tumors, differing between sBBC and mBBC. mBBC phenotype shares many features with BOCS tumors.