Introduction and Purpose: The frequency of bilateral breast cancer is 1.4-11.0% among all breast cancers.It can present as synchronous (SC) or metachronous (MC). Data regarding clinical course of bilateral breastcancer are scarce. In this study, we therefore evaluated demographic, pathological and clinical characteristics,treatments and responses in bilateral breast cancer cases; making distinctions between metachronous-synchronousand comparing with historic one-sided data for the same parameters. Materials and Methods: One hundred fiftybilateral breast cancer cases from ten different centers between 2000 and 2011 were retrospectively scanned.Age of the cases, family history, menopausal status, pathological features, pathological stages, neoadjuvant,surgery, adjuvant and palliative chemotherapy/radiotherapy were examined in the context of the first and secondoccurrence and discussed with reference to the literature. Results: Metachronous and synchronous groups showedsimilar age, menopausal status, tumor type, HER2/neu expression; the family history tumor grade, tumor stage,ER-negativity rate, local and distant metastases rates, surgery, adjuvant chemotherapy application rates wereidentified as significantly different. Palliative chemotherapy response rate was greater in the metachronousgroup but median PFS rates did not differ between the groups. Conclusion: Although bilateral breast cancer isnot frequent, MC breast cancer is different from SC breast cancer by having more advanced grade, stage, lessER expression, more frequent rates of local relapse and distant metastasis and better response to chemotherapyin case of relapse/metastasis.
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