Importance: There are few data on state variation in racial and ethnic disparities in incidence of triple-negative breast cancer (TNBC) in the US, limiting the ability to inform state-level health policy developments toward breast cancer equity.
Objective: To quantify between and within racial and ethnic disparities in TNBC incidence rates (IRs) among US women across states.
Design, setting, and participants: This cohort study using population-based cancer registry data included data for all women with TNBC diagnosed from January 1, 2015, to December 31, 2019, identified in the US Cancer Statistics Public Use Research Database. Data were analyzed from July through November 2022.
Exposures: State and race and ethnicity (Hispanic, non-Hispanic American Indian or Alaska Native, non-Hispanic Asian or Pacific Islander, non-Hispanic Black, or non-Hispanic White) abstracted from medical records.
Main outcomes and measures: The main outcomes were diagnosis of TNBC, age-standardized IR per 100 000 women, state-specific incidence rate ratios (IRRs) using the rate among White women in each state as a reference for between-population disparities, and state-specific IRRs using the race and ethnicity-specific national rate as a reference for within-population disparities.
Results: The study included data for 133 579 women; 768 (0.6%) were American Indian or Alaska Native; 4969 (3.7%), Asian or Pacific Islander; 28 710 (21.5%), Black; 12 937 (9.7%), Hispanic; and 86 195 (64.5%), White. The TNBC IR was highest among Black women (25.2 per 100 000 women), followed by White (12.9 per 100 000 women), American Indian or Alaska Native (11.2 per 100 000 women), Hispanic (11.1 per 100 000 women), and Asian or Pacific Islander (9.0 per 100 000 women) women. Racial and ethnic group-specific and state-specific rates substantially varied, ranging from less than 7 per 100 000 women among Asian or Pacific Islander women in Oregon and Pennsylvania to greater than 29 per 100 000 women among Black women in Delaware, Missouri, Louisiana, and Mississippi. Compared with White women, IRRs were statistically significantly higher in 38 of 38 states among Black women, ranging from 1.38 (95% CI, 1.10-1.70; IR, 17.4 per 100 000 women) in Colorado to 2.32 (95% CI, 1.90-2.81; IR, 32.0 per 100 000 women) in Delaware; lower in 22 of 22 states among Asian or Pacific Islander women, varying from 0.50 (95% CI, 0.34-0.70; IR, 5.7 per 100 000 women) in Oregon to 0.82 (95% CI, 0.75-0.90; IR, 10.5 per 100 000 women) in New York; and did not differ among Hispanic and American Indian or Alaska Native women in 22 of 35 states and 5 of 8 states, respectively. State variations within each racial and ethnic population were smaller but still substantial. For example, among White women, compared with the national rate, IRRs varied from 0.72 (95% CI, 0.66-0.78; IR, 9.2 per 100 000 women) in Utah to 1.18 (95% CI, 1.11-1.25; IR, 15.2 per 100 000 women) in Iowa, 1.15 (95% CI, 1.07-1.24; IR, 14.8 per 100 000 women) in Mississippi, and 1.15 (95% CI, 1.07-1.24; IR, 14.8 per 100 000 women) in West Virginia.
Conclusions and relevance: In this cohort study, there were substantial state variations in racial and ethnic disparities in TNBC incidence, with Black women in Delaware, Missouri, Louisiana, and Mississippi having the highest rates among all states and racial and ethnic populations. The findings suggest that more research is needed to identify factors contributing to the substantial geographic variations in racial and ethnic disparities in TNBC incidence to develop effective preventive measures and that social determinants of health contribute to the geographic disparities in TNBC risk.