Abstract 4862: Rural-urban disparities in early-onset breast cancer amongst US women aged 20-49, trends from 2000-2020

Abstract Purpose: To characterize rural-urban disparities of breast cancer (BC) incidence among younger women by stage and race/ethnicity. Background: Cancer incidence in younger adults is increasing, but trends and disparity patterns in early-onset BC are not well-described for women aged <50 years. Current screening guidelines recommend against routine screening until age 40 for various perceived harms that outweigh benefits which can lead to delayed diagnosis and more aggressive stage when BC is identified among younger women. It is unclear how BC incidence patterns such as stage at diagnosis and race/ethnicity differ by rurality, as rural residents may experience geographic isolation, lower socioeconomic status (SES), higher rates of cancer risk behaviors, and limited access to healthcare, compared to urban residents. Methods: We used incidence data from the North American Association of Central Cancer Registries to identify trends in early-onset BC among women aged 20-49 from 2000-2020, stratified by rurality (2013 USDA Rural-Urban Continuum Codes) and to explore patterns by stage and race/ethnicity. We extracted age-adjusted incidence rates (IR) [adjusted to 2000 US Standard Population] for each year and detected significant increasing or decreasing trends over time using the Joinpoint Regression Program. The annual percentage change (APC) for IR trends were calculated. Results: Of the 854,590 patients, 88% lived in urban areas (12% rural). Cumulatively over 2000-2020, we observed similar average APCs for early-onset BC both in urban (IR = 68.8 per 100,000; avg. APC +0.37, 95% CI 0.23, 0.50) and rural areas (IR = 65.1 per 100,000; avg. APC +0.35, 95% CI 0.14, 0.57). Rural areas did not significantly trend upwards until 2010-2020 (APC +0.71, 95% CI 0.38, 1.05). Rates for localized stage increased from 2000-2020 (APC +0.69%, 95% CI 0.48, 0.89) for urban areas, but declined in rural areas between 2000-2008 (APC -0.77, 95% CI -1.33, -0.20), only to increase again from 2008-2020 (APC +1.01, 95% CI 0.68, 1.34). In rural areas, there is a corresponding dramatic increase in distant stage BC diagnosed between 2000-2007 (APC +5.99%, 95% CI 2.29, 9.93) but slowed in the period after (2007-2020 APC +1.35, 95% CI 0.22, 2.51). While the rate remained stable for Hispanics living in both urban and rural areas, Non-Hispanic Whites (2000-2020 APC +0.59, 95% CI 0.46, 0.72), Non-Hispanic Blacks (2000-2009 APC +0.85, 95% CI 0.33, 1.37), and Other Non-Hispanic racial groups (2000-2020 APC +1.27, 95% CI 1.16, 1.58) saw significant increased rates in urban areas over time. Conclusions: Overall, early-onset BC has risen over the past 20 years in both urban and rural areas, but clear differences exist by stage at diagnosis and race/ethnicity. More research is needed to understand how SES, healthcare access, screening recommendations, and additional cancer risk factors can modulate BC incidence and disparities among younger women. Citation Format: Katherine L. Ho, Avonne Connor. Rural-urban disparities in early-onset breast cancer amongst US women aged 20-49, trends from 2000-2020 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4862.