Bilateral breast cancer, synchronous and metachronous; differences and outcome.

The aims of this study were twofold: to analyze the incidence of patients having synchronous or metachronous bilateral invasive breast cancer (SBBC and MBBC) and to assess the characteristics and outcome compared to those having unilateral breast cancer (UBC). The used data were obtained from our prospective population-based cohort study which had been started in 1983. Bilateral breast cancer (BBC) was categorized as SBBC (≤3 months of the first primary) or MBBC (>3 months after the first primary). The incidence of SBBC was 1% and that of MBBC 7.0 %. Patients with UBC showed more ductal carcinoma compared to patients with BBC. MBBC status was an independent significant predictor of local failure (HR 1.9; 95% CI 1.3-2.7). SBBC status was an independent predictor of distant metastases (HR 2.6; 95% CI 1.4-4.5). Overall survival (OS) was better for MBBC (HR 0.6; 95% CI 0.4-0.8) and worse for SBBC (HR 2.3; 95% CI 1.5-3.6) compared to UBC. We noted: (1) MBBC showed a significant higher local failure compared to UBC, (2) SBBC, compared to MBBC and UBC had a significant higher distant metastases rate, (3) disease-specific survival and OS were significantly worse for SBBC compared to UBC and MBBC, and (4) that the OS for MBBC compared to UBC, was significantly better.