Background: Studies have shown that contralateral breast cancer (CBC) portends worse survival compared to unilateral breast cancer (UBC), but few studies have been conducted in the United States, and survival is usually examined from the time of CBC development.
Methods: Utilizing the Surveillance, Epidemiology, and End Results database, we selected 83,001 newly diagnosed breast cancer patients from 1998 to 2005. The time interval between the initial cancer and CBC was used as a time-dependent variable in a Cox regression analysis to examine overall survival (OS) and disease-specific survival (DSS) between UBC and CBC.
Results: Overall, 2130 patients (2.6 %) developed a CBC, 47.2 % within 5 years and 52.8 % ≥ 5 years. Most stage I patients (61.9 %) developed a stage I CBC, and a majority of stage II patients (51.6 %) developed a stage I CBC (p < 0.001). There was a median follow-up of 8.7 years. After adjustment, patients who developed a CBC 4 years after their initial breast cancer had worse DSS compared to patients with UBC (hazard ratio 1.36, 95 % confidence interval 1.03-1.79). Those patients who developed their CBC 8 years after their initial breast cancer had improved DSS (hazard ratio 0.37, 95 % confidence interval 0.20-0.67). Similar trends were observed for OS. Similar trends for OS and DSS were observed for estrogen receptor-negative women and women <50 years old.
Conclusions: Development of a CBC early is associated with worse survival, but CBC development later on is associated with improved survival. Future studies are needed that can assist physicians with how to predict whether a patient will develop a CBC early on.