Persistent Racial Disparities in Breast Cancer Incidence by Stage and Subtype in a High-Burden State.

INTRODUCTION: Breast cancer incidence varies by race, stage at diagnosis, and molecular subtype. However, these patterns are often obscured in overall estimates, particularly in high-burden settings. This study examined incidence trends overall and by race, stage at diagnosis, and molecular subtype among women in Mississippi. METHODS: We used population-based data from the Mississippi Cancer Registry, including Black and White women aged ≥ 18 years diagnosed with primary breast cancer from 2010 to 2019. Age-adjusted incidence rates (IRs) per 100,000 population were standardized to the 2000 United States standard population. Trends were assessed using Joinpoint regression estimating average annual percent changes (AAPCs) and annual percent changes (APCs). Multivariable Poisson regression estimated incidence rate ratios (IRRs) with 95% confidence intervals (CIs). RESULTS: Among 21,130 women (64.4% White; 35.6% Black), the overall age-adjusted IR was 166.0 per 100,000 with no significant change over time (AAPC = 0.48%; 95% CI: -0.27 to 1.24). Black women had higher incidence than White women (178.0 vs. 159.1). Among White women, incidence increased modestly (AAPC = 0.60%; 95% CI: 0.06-1.13). Trends among Black women were not significant overall (AAPC = 0.36%; 95% CI: -0.25 to 1.04) but increased from 2014 to 2019 (APC = 1.95%; 95% CI: 0.77-4.26) after an initial decline. Localized-stage incidence increased in both groups, while Black women had higher regional- and distant-stage incidence. In adjusted models, Black women had higher incidence of HER2-overexpressing (IRR = 1.55; 95% CI: 1.15-2.10) and triple-negative cancer (IRR = 2.35; 95% CI: 1.74-3.17) than White women. CONCLUSION: Overall incidence remained stable, but substantial heterogeneity across subgroups underscores the need for stratified surveillance and equity-focused cancer control strategies in high-burden settings.