Comparison of prognosis and clinical features between synchronous bilateral and unilateral breast cancers.

PURPOSE The clinical significance of synchronous bilateral breast cancer (SBBC) is unclear and its influence on prognosis is controversial. Our study objective was to determine the epidemiological features, tumor characteristics, and prognosis of SBBC in comparison with those of unilateral breast cancer (UBC). METHODS A total of 3675 breast cancer patients diagnosed and treated between 2000 and 2014 were evaluated. Of these patients, 132 (3.6%) had bilateral breast cancer, including 55 patients (1.5%) with SBBC and 77 (2.1%) with metachronous bilateral breast cancer (MBBC). The patient demographic characteristics, including survival data and clinicopathological tumor characteristics, were obtained from medical charts and compared between the patients with SBBC and those with UBC. RESULTS The median age in the SBBC group was 51 years (range 32-77). The mastectomy rate was higher in the SBBC group (72.7%) than in the UBC group (66.6%) (p=0.08). In both the SBBC and UBC groups, the baseline clinicopathological features and the history of treatment with radiotherapy and chemotherapy were similar. Infiltrating ductal carcinoma was the most common histology in both groups. Lobular histology was more frequent in the SBBC group (36.3%) than in the UBC group (17.1%; p<0.001). Stage IV disease at initial presentation was more frequent in the SBBC group than in the UBC group (34.5 vs 8.7%, p<0.001). The 5-year disease-free survival (DFS) rates were 90% and 82% in the SBBC and UBC groups, respectively (p=0.99). The 5-year overall survival (OS) rates were 83% and 88%, respectively (p=0.357). The multivariate Cox regression analysis, including stage, hormone receptor status, grade, and SBBC, revealed that the presence of SBBC was not associated with OS (hazard ratio 0.929; 95% confidence interval, 0.455-0.1894, p=0.839). CONCLUSION Despite the differences in histology, initial stage, and other characteristics, the prognoses of UBC and SBBC were similar.