Does Having Bilateral Breast Cancer or Synchronous Bilateral Breast Cancer Shorten Survival? Comparison of Unilateral with Metachronous and Synchronous Bilateral Breast Cancer Using Propensity Score Analysis: A Retrospective Single-Center Analysis
Authors: Ozler Talar , Cosar Rusen , Sut Necdet , Nurlu Dilek , Parlar Şule , Ateş Sinan , Dertli Mert Hacı , Kavuzlu Yusuf , Kavukcu Sekip , Chousein Mert , Yıldız Gokay , Tunçbilek Nermin , Hacıoglu Muhammet Bekir , Tastekin Ebru , Topaloğlu Sernaz 
Published: November 2024

Introduction: Bilateral breast cancer can present in two ways: as synchronous bilateral breast cancer (SBBC) when diagnosed at the same time as the first tumor or within 3, 6, or 12 months after the initial diagnosis, or as metachronous bilateral breast cancer (MBBC) if diagnosed after a longer period. The characteristics of patients with bilateral and unilateral breast cancer at the time of diagnosis or during follow-up have been compared, focusing on the differences in disease-free survival and overall survival between these groups. Prognostic factors contributing to this difference have been investigated.
Materials and Methods: A total of 1,959 patients with a diagnosis of invasive carcinoma were included in the study. Of the 1959 patients whose records we reviewed, 1888 (96.4%) had unilateral breast cancer, and 71 (3.6%) had bilateral breast cancer. Among the bilateral breast cancer patients n=47 were metachronous, and n=24 were synchronous. The characteristics of patients with bilateral and unilateral breast cancer at the time of diagnosis or during follow-up have been compared, focusing on the differences in disease-free survival and overall survival between these groups. To eliminate numerical imbalance, propensity score analysis was performed between unilateral and bilateral breast cancer groups using the optimum matching algorithm (optimum, 1:1).
Results: In our series, the DFS duration was 132.24 ± 13.86 months for unilateral breast cancer, 170.74 ± 14.59 months for metachronous bilateral breast cancer (p=0.257), and 132.77 ± 30.76 months for synchronous bilateral breast cancer (p=0.770). The OS duration was 170.48 ± 14.22 months for unilateral breast cancer, while a statistically significant difference was found in metachronous bilateral breast cancer at 215.04 ± 10.66 months (p=0.015). When comparing unilateral breast cancer with synchronous bilateral breast cancer, the difference disappeared with a duration of 164.86 ± 30.65 months (p=0.872). SBBC, which had the lowest OS duration, showed a statistically significant difference compared to MBCC, similar to that observed in unilateral breast cancer (p=0.027). In Cox regression multivariate analysis, having synchronous bilateral breast cancer increased the risk of death by 2.5 times, even if it was not at the level of statistical significance. Having metachronous bilateral breast cancer reduced the risk of death by 2.4 times.
Conclusion:. The fact that SBBC has the lowest survival rate despite more aggressive treatments should be considered a poor prognostic factor for survival on its own SBBC should be evaluated as a separate subgroup. Therefore, SBBC should be evaluated as a separate subgroup. In other words, evaluating MBBC in the same basket within BBC prevents us from seeing that patients with synchronous breast cancer have a poor prognosis on their own. New treatment strategies are needed for SBBC.