Multiple mediation analysis of racial disparity in breast cancer survival

Abstract

Background: Racial (Black vs. White) disparities in breast cancer survival have proven difficult to mitigate. Targeted strategies aimed at the primary factors driving the disparity offer the greatest potential for success. The purpose of this study was to use multiple mediation analysis to identify the most important mediators of the racial disparity in breast cancer survival.

Methods: This was a retrospective cohort study of non-Hispanic Black and non-Hispanic White women diagnosed with invasive breast cancer in Florida between 2004 and 2015. Cox regression was used to obtain unadjusted and adjusted hazard ratios (HR) with 95% confidence intervals (CI) for the association of race with 5- and 10-year breast cancer death. Multiple mediation analysis of tumor (advanced disease stage, tumor grade, hormone receptor status) and treatment-related factors (receipt of surgery, chemotherapy, radiotherapy, and hormone therapy) was used to determine the most important mediators of the survival disparity.

Results: The study population consisted of 101,872 women of whom 87.0% (n = 88,617) were White and 13.0% were Black (n = 13,255). Black women experienced 2.3 times (HR, 2.27; 95% CI, 2.16-2.38) the rate of 5-year breast cancer death over the follow-up period, which decreased to a 38% increased rate (HR, 1.38; 95% CI, 1.31-1.45) after adjustment for age and the mediators of interest. Combined, all examined mediators explained 73% of the racial disparity in 5-year breast cancer survival. The most important mediators were: (1) advanced disease stage (44.8%), (2) nonreceipt of surgery (34.2%), and (3) tumor grade (18.2%) and hormone receptor status (17.6%). Similar results were obtained for 10-year breast cancer death.

Conclusion: These results suggest that additional efforts to increase uptake of screening mammography in hard-to-reach women, and, following diagnosis, access to and receipt of surgery may offer the greatest potential to reduce racial disparities in breast cancer survival for women in Florida.

Keywords: Breast cancer; Epidemiology; Mediation analysis; Racial disparity; Survival.