Racial and Ethnic Disparities in Synchronous and Metachronous Bilateral Breast Cancer

Significant racial and ethnic disparities exist in breast cancer treatment and survival. However, studies characterizing these disparities among patients developing bilateral breast cancers (BBC) are lacking. The purpose of this study is to understand the association between race and ethnicity, sociodemographic factors, clinical variables, treatment, and mortality in patients with BBC--synchronous bilateral breast cancer (sBBC) or metachronous bilateral breast cancer (mBBC).

Patients diagnosed with mBBC or sBBC in the Surveillance, Epidemiology, and End Results program between 2010 and 2016 were examined. sBBC was defined as contralateral breast cancer <1 year after the initial cancer diagnosis, and mBBC was contralateral cancer ≥1 year. Univariable analysis examined sociodemographic, clinical, and treatment variables. Kaplan-Meier curves and Cox regression models evaluated disease-specific mortality.

Of the 11,493 patients that met inclusion criteria, 9575 (83.3%) had sBBC, and 1918 (16.7%) had mBBC. There were significant racial and ethnic differences in stage, tumor subtype, surgical management, and chemotherapy within sBBC and mBBC groups. On adjusted multivariate analysis of all BBC patients, Black race (HR 1.42; 95%CI 1.11-1.80; p<0.005; Ref White) was associated with a higher disease-specific mortality. Conversely, patients with mBBC had a 25% relative risk reduction in disease-specific mortality (HR 0.75; 95%CI 0.61-0.92; p<0.01) compared to sBBC. Subset analysis suggested Black Race modified the effect of sBBC on mortality (p<0.0001).

Among patients with BBC, there are racial and ethnic disparities in clinical characteristics, treatment, and mortality. Future studies should focus on strategies to reduce these disparities.