Illuminating Bilateral Breast Cancer: A Multicenter Experience and Clinical Observations

Background and Objectives: Although breast cancer is the most common type of cancer among women, bilateral breast cancer (BBC) remains exceedingly rare. BBC can present as either synchronous (SBBC) or metachronous (MBBC) disease. Data regarding the clinical characteristics of BBC are limited. In this study, we aimed to share our multicenter, retrospective experience on the clinicopathological and demographic features of SBBC and MBBC, their survival outcomes, and the factors influencing survival, in light of current knowledge. Material and Method: A total of 125 patients who were treated and followed between 2015 and 2024 across six different centers were included in the study. The patients were categorized into synchronous (SBBC) and metachronous (MBBC) groups. Their clinicopathological characteristics were analyzed, along with disease-free survival (DFS) and 5-year overall survival (OS) outcomes. Results: DFS was 5.7 years in the SBBC group and 5.6 years in the MBBC group (p = 0.95). The 5-year OS rate was 95.2% in the MBBC group and 80.7% in the SBBC group (p = 0.035). Hormone receptor negativity was identified as an independent risk factor for lower DFS in the overall patient cohort (HR: 0.55, 95% CI: 0.31-0.98, p = 0.04). Conclusion: Significant differences were found between the SBBC and MBBC groups in terms of hormone receptor status, presence of an invasive lobular carcinoma component, recurrence/metastasis status, and molecular subtype discordance between the two primary tumors. Although DFS did not significantly differ between the groups, the 5-year OS was significantly higher in the MBBC group. In multivariate regression analysis, hormone receptor negativity was identified as an independent risk factor for decreased DFS among all BBC patients. Our study is noteworthy for shedding light on the clinical features of BBC in the context of current knowledge and for its multicenter design.