Background: Racial disparities in breast cancer survival have been well documented. This study examines the association of race/ethnicity and socioeconomic status (SES) on breast cancer-specific mortality in a large population of women with invasive breast cancer.
Methods: We identified 179,143 cases of stages 1-3 first primary female invasive breast cancer from the California Cancer Registry from January, 2000 through December, 2010. Cox regression, adjusted for age, year of diagnosis, grade, and ER/PR/HER2 subtype, was used to assess the association of race/ethnicity on breast cancer-specific mortality within strata of stage and SES. Hazard ratios (HR) and 95% confidence intervals were reported.
Results: Stage 1: There was no increased risk of mortality for any race/ethnicity when compared with whites within all SES strata. Stage 2: Hispanics (HR = 0.85; 0.75, 0.97) in the lowest SES category had a reduced risk of mortality.. Blacks had the same risk of mortality as whites in the lowest SES category but an increased risk of mortality in the intermediate (HR = 1.66; 1.34, 2.06) and highest (HR = 1.41; 1.15, 1.73) SES categories. Stage 3: Hispanics (HR = 0.74; 0.64, 0.85) and APIs (HR = 0.64; 0.50, 0.82) in the lowest SES category had a reduced risk while blacks had similar mortality as whites. Blacks had an increased risk of mortality in the intermediate (HR = 1.52; 1.20, 1.92) and highest (HR = 1.53; 1.22, 1.92) SES categories.
Conclusions: When analysis of breast cancer-specific mortality is adjusted for age and year of diagnosis, ER/PR/HER2 subtype, and tumor grade and cases compared within stage and SES strata, much of the black/white disparity disappears. SES plays a prominent role in breast cancer-specific mortality but it does not fully explain the racial/ethnic disparities and continued research in genetic, societal, and lifestyle factors is warranted.