Abstract P5-08-14: Synchronous bilateral breast cancer compared to unilateral breast cancer: A population based study
Authors: Yadav S , Zakalik D 
Published: March 2017

Abstract
Introduction: The clinical presentation and outcome of synchronous bilateral invasive breast cancer compared to unilateral breast cancer is not well studied. In this study, we present a population based comparison of tumor characteristics and survival between invasive unilateral and bilateral breast cancer.
Methods: Data from National Cancer Institute- Surveillance, Epidemiology and End Results (SEER) was analyzed to identify women who had a diagnosis of invasive ductal carcinoma (ICD-O-3: 8500/3) between the years 2000 and 2013. Women who were diagnosed with an invasive contralateral breast cancer within two months of initial diagnosis were classified under synchronous bilateral breast cancer group. Women who developed a contralateral breast cancer between three to twelve months of diagnosis were excluded. All women who did not develop a second breast cancer, or developed it after twelve months of initial diagnosis were classified under unilateral breast cancer group. Patients with an in-situ breast cancer diagnosis in the contralateral breast within twelve months of diagnosis of invasive ductal carcinoma were excluded. Patients with metastatic disease and unknown stage at presentation were excluded. Tumor characteristics and survival were compared between the two groups using the index case only. Mann-Whitney U test was used for continuous variables while Chi-square test was used for categorical variables. Kaplan-Meier curves and Cox proportional hazard regression models were used to compare survival. All data analysis was performed using SPSS 21.
Results: A total of 414,766 patients met our inclusion criteria. Of these, 3,590 patients were in the synchronous bilateral breast cancer group, while 411,176 were in the unilateral breast cancer group. Compared to unilateral breast cancer patients, bilateral breast cancer patients were slightly older (62 Vs 59, p&lt;0.05) and were more likely to have higher T, N or overall stage at presentation. Their tumors were also more likely to be estrogen or progesterone receptor positive (p&lt;0.05). Patients with bilateral breast cancer also had higher rates of mastectomy (63.3% Vs 39.1%, p&lt;0.05).
Patients with bilateral breast cancers had a significantly worse survival compared to patients with unilateral breast cancer (Table 1). In a multivariate Cox proportional hazard regression, adjusting for age at diagnosis, T-Stage, N-Stage, overall stage, hormone receptor status, type of surgical treatment and radiation therapy, bilateral breast cancers had a mortality hazard ratio of 1.48 (95% CI: 1.35 – 1.62, p&lt;0.001) compared to unilateral breast cancers.
Conclusions: Our study demonstrates that bilateral breast cancer has a worse prognosis compared to invasive unilateral breast cancer. These findings have important implications for patients, and contribute to our understanding of the unique outcomes of bilateral breast cancer which will guide treatment and follow up.
Table 1: Survival of unilateral vs bilateral breast cancer Unilateral breast cancerBilateral breast cancer5-year cause specific survival91.7%86.5%10-year cause specific survival86.1%77.7%
Citation Format: Yadav S, Zakalik D. Synchronous bilateral breast cancer compared to unilateral breast cancer: A population based study [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P5-08-14.