Abstract 6207: Trends in breast cancer incidence-based mortality among US women aged 20-49 by molecular subtypes and race

Background: Breast cancer incidence is rising in women aged 20-49 years, yet data on trends in mortality for this age group are limited. Mortality varies by several factors, underscoring the need for comprehensive analyses. We, therefore, investigated trends in breast cancer incidence-based mortality (IBM) by race and molecular subtypes. Methods: We performed a population-based study of women aged 20-49 years diagnosed with breast cancer between 2010 and 2020 using SEER 17-registry data. We applied IBM method to evaluate mortality trends by molecular subtype and race/ethnicity. We used Joinpoint regression models to identify changes in IBM trends, using annual percent changes (APC). Additionally, we evaluated breast cancer survival rates by race/ethnicity. Results: We analyzed data on 11,661 breast cancer deaths among women aged 20-49 years. Overall, IBM declined from 9.70/100,000 in 2010 to 1.47/100,000 in 2020. The declines occurred in all subtypes and racial/ethnic groups, with some differences in the points of inflexion. IBM for luminal A decreased consistently from 2010, with more marked decline from 2017 (APC, -32.88; 95%CI, -55.17 to -21.30). TNBC followed a similar pattern, with marked decline in 2018 (APC, -32.82; 95%CI, -41.47 to -17.79). Non-Hispanic Black (NHB) women had the highest IBM in 2010 (16.56/100,000) and 2020 (3.41/100,000) compared with Non-Hispanic White (NHW) women (9.18/100,000 in 2010 and 1.16/100,000 in 2020). Declines in IBM in NHB women become pronounced from 2016 (APC, -24.15; 95% CI -34.36 to -17.92), narrowing the gap with other racial groups. Significant declines in IBM for non-Hispanic Asian/Pacific Islander (API) women started earlier from 2013, compared to 2017 for NHW, non-Hispanic American Indian/Alaska Native, and Hispanic women. Survival analyses showed that NHB women had the worst survival outcomes, while NHW and non-Hispanic API had the best. Conclusion: IBM among US women aged 20-49 years with breast cancer declined significantly from 2010 to 2020, with variations by molecular subtype and race/ethnicity. The rapid decline in IBM after 2016-2018 likely reflects advancements in breast cancer management, particularly in novel treatments. Although NHB women still have the highest IBM, the differences have narrowed in recent years. Efforts should continue to focus on further enhancing access to early screening for high-risk women and effective treatment to fully mitigate racial disparities in mortality. Citation Format: Yueshiu Lyu, Suleepon Uttamapinan, Adetunji T. Toriola. Trends in breast cancer incidence-based mortality among US women aged 20-49 by molecular subtypes and race [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular s); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1): nr 6207.