Abstract B055: Racial and ethnic disparities in the risk of contralateral breast cancer among primary breast cancer survivors in the US (1992-2023)

Abstract

Breast cancer survivors have an increased risk of developing contralateral breast cancer (CBC), with approximately 1 in 30 developing CBC within 10 years of their initial diagnosis. However, few U.S. studies have examined CBC risk by racial and ethnic differences or by estrogen receptor (ER) subtype of the contralateral tumor. We investigated CBC risk among primary breast cancer survivors relative to the general population by race and ethnicity and ER subtype of CBC. Using the SEER-12 registries, this analysis included 522,407 women aged 20-84 years diagnosed with a first primary unilateral invasive non-metastatic breast cancer between 1992 and 2022 who survived at least 1 year. We estimated standardized incidence ratios (SIRs) and 95% confidence intervals (CIs) by race and ethnicity [Hispanic (N = 63,011), non-Hispanic American Indian/Alaska Native (AI/AN) (N = 2,305), non-Hispanic Asian or Pacific Islander (API) (N = 64,784), non-Hispanic Black (N= 41, 056), and non-Hispanic White (N = 350,516)], calendar year of diagnosis, age at diagnosis, and ER status of CBC, using comparisons with a race- and ethnicity- matched general population. Cumulative incidence of CBC accounting for competing risks was estimated by race and ethnicity. Over a median follow-up of 9.5 years (interquartile range [IQR] 4.7-16.2 years), 19,202 survivors developed CBC (2,019 Hispanic, 75 AI/AN, 2,106 API, 1,668 Black, and 13,334 White survivors). Compared with the race- and ethnicity-matched general population, CBC risk was elevated across all racial and ethnic groups, with the highest relative risk observed among Hispanic survivors (SIR 5.03, 95% CI 4.81-5.25) and the lowest among White survivors (SIR 3.23, 95% CI 3.17-3.28). SIRs were highest among women diagnosed before age 50 years, particularly among Hispanic (SIR 8.52, 95% CI 7.97-9.10) and Black survivors (SIR 7.13, 95% CI 6.57-7.70). ER-negative CBC showed the greatest relative risk, especially among Hispanic (SIR 7.60, 95% CI 6.93-8.30) and Black survivors (SIR 5.80, 95% CI 5.31-6.31), whereas the lowest risk was observed for ER-positive CBC among White survivors (SIR 3.01, 95% CI 2.95-3.07). CBC risk declined over calendar year of diagnosis across all racial and ethnic groups (P-trend<0.001), particularly among Hispanic survivors with SIRs decreasing from 6.54 (95% CI 6.00, 7.10) in 1992-1997 to 2.84 (95% CI 2.18, 3.58) in 2018-2023 (P-trend <0.001). Cumulative incidence at 10 years remained highest among Black survivors and lowest among AI/AN ([3.9%, 95% CI 3.77-4.21%] vs. [2.49%, 95% CI 1.89-3.21%]). CBC risk is heterogenous among breast cancer survivors by race and ethnicity. Whereas Hispanic and Black survivors had the highest relative risks across time, age, and ER subtype, Black survivors had the highest absolute risk. These findings underscore the need to identify the clinical, biological, and social factors which can contribute to the development of targeted prevention strategies to mitigate these disparities. Michelle O. Sodipo, Jacqueline B. Vo, Jaimie Z. Shing, Amber N. Hurson, Yuehan Wang, Stephanie T.Y. Ho, Angelina Cho, Angel H. Pajimola, Rochelle E. Curtis, Amy Berrington de Gonzalez, Lene H.S. Viega, Gretchen L. Gierach. Racial and ethnic disparities in the risk of contralateral breast cancer among primary breast cancer survivors in the US (1992-2023) [abstract]. In: Proceedings of the 19th AACR Conference on the Science of Cancer Health Disparities; 2026 Oct 18-21; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2026;35(10 Suppl):Abstract nr B055.