Rural-urban disparities in breast cancer incidence among US women aged 20-49: trends by race/ethnicity, stage, poverty, and state from 2000-2019.

[PURPOSE] To explore patterns in rising breast cancer (BC) incidence trends by rurality among younger women aged < 50.

[METHODS] We analyzed incidence data from the North American Association of Central Cancer Registries to assess trends in early-onset BC (ages 20-49) from 2000-2019 in the United States, stratified by rurality (USDA rural-urban continuum codes), stage, race/ethnicity, poverty (< 5%, 5- < 10%, 10- < 20%, ≥ 20% below poverty), and state. We extracted age-adjusted incidence rates (aIR) (2000 US standard population) for each year and used the joinpoint regression program to detect significant trends over time, calculating annual percentage changes (APC) and average annual percentage changes (AAPC).

[RESULTS] Of the 836,012 patients (87.7% urban, 12.3% rural), BC incidence was similar in urban (aIR = 69.3/100,000; AAPC + 0.52%) and rural counties (aIR = 61.6/100,000; AAPC + 0.43%) from 2000-2019. Localized stage BC increased (APC + 1.54%) in urban counties but declined in rural counties (APC = - 0.77%) before rising again (APC + 1.18%). Rates increased across all races/ethnicities, with Non-Hispanic Black women having the highest rates regardless of rurality (aIR = 71.8; aIR = 71.6). Four states (Idaho [AAPC =  + 1.03%], Montana [AAPC =  + 1.26%], North Dakota [AAPC =  + 1.10%], and South Dakota [AAPC =  + 1.03%]) had sustained significant annual increases (AAPC is > 1).

[CONCLUSIONS] Early-onset BC rose between 2000-2019 in both urban and rural areas, with differences by stage, race and ethnicity, poverty, and state. More research is needed to understand how rurality intersects with SES, healthcare access, screening, and incidence for women aged 20-49.