Abstract P4-09-17: Case-Matching Study Comparing Outcome of Unilateral and Synchronous Bilateral Breast Cancer

Abstract

Abstract Background: Several retrospective studies have demonstrated worse outcomes for patients with synchronous bilateral breast cancer (SBBC) compared to unilateral breast cancer. This study aimed to determine whether SBBC outcomes can be estimated accurately from the characteristics of the higher-risk cancer. Material and Methods: In the province of British Columbia, Canada, women newly diagnosed with invasive breast cancer between 1989 and 2000, without metastatic or inflammatory presentation, were identified: 207 with SBBC (< 2 months apart) and 15,497 with unilateral breast cancer. Their breast cancer-specific survival (BCSS) outcomes were compared. Using 10-year BCSS estimates, the higher-risk cancer of each SBBC was determined. The priority sequence of matching of the prognostic and predictive variables was: positive lymph node number, primary tumor size, age, grade, lymphovascular invasion status, estrogen receptor status, type of local therapy, margin status, treating clinic, diagnosis year and systemic therapy use. A software program was employed on the 15,497-case cohort to select three unilateral cases that matched the maximum number of variables for the higher-risk cancer of each SBBC case, thereby generating a matched 621-case unilateral cohort. Results: At a median follow-up of 10.2 years, the 10-year BCSS was significantly lower for the SBBC cohort, 71% (95%CI 63 — 77) than for the 15,497-case unilateral cohort, 81.1% (95%CI 80.5 — 81.8) (p < 0.001). However, the SBBC cohort had significantly higher median age and stage at presentation. After the matching, there was no significant difference for the eleven variables between the SBBC cohort and the 621-case unilateral cohort. The 10-year BCSS was 71% (95%CI 63-77) for the SBBC cohort and 74% (95%CI 69-77) for the matched 621-case unilateral cohort. Discussion: BCSS was similar between the SBBC cohort and the unilateral cohort matched to the higher-risk SBBC. Therefore, the outcome of women with SBBC is best estimated from their higher-risk cancer. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P4-09-17.