Abstract B021: Early onset uterine corpus cancer incidence rates and 5-year relative survival by histologic subtype and race/ethnicity among women aged 20-49 years

Abstract Purpose: Uterine cancer, including early onset cases, is increasing among all women, particularly in minority populations. Despite nearly 25% of cancers occurring in younger women, changes in tumor characteristics (e. g. , histology) by race/ethnicity remain poorly understood. We examined incidence rates and 5-year relative survival of uterine cancer among women aged 20-49, overall and by race/ethnicity and histology. Methods: We used the Surveillance, Epidemiology, and End Results Program (SEER 22) Research Plus Data, representing 47. 9% of the total U. S. population. We included women aged 20-49 years with microscopically confirmed malignant uterine cancer (diagnosed 2000-2019) to calculate age-adjusted incidence and age-standardized 5-year relative survival (2000-2018) overall and by race/ethnicity and histology. Time trends were described across two time periods: 2000-2009 and 2010-2019. All analyses were conducted using SEER*Stat; incidence rates were presented for per 100, 000 population. Results: We included 57, 128 cases (55% Non-Hispanic NH-White, 9% NH-Black, 10% NH-Asian/Pacific Islander PI, and 25% Hispanic). From the period of 2000-2009 to 2010-2019, the proportion of cases that were 20-29 and 30-39 increased by 1% and 4%, respectively. Overall, incidence increased over time for all women (8. 7 in 2000-2009 to. 10. 4 in 2010-2019), and increases were observed for both endometrioid and non-endometrioid subtypes. In the most recent period, rates were highest for endometrioid subtypes (8. 4), followed by sarcomas (1. 0), and non-endometrioid subtypes (0. 7). Rates for endometrioid and non-endometrioid cancers were highest in Hispanics (9. 9 and 0. 8) and NH-Asian/Pacific Islanders (9. 7 and 0. 8), respectively and lowest in NH-Blacks (5. 5 and 0. 6). Rates of sarcomas were highest in NH-Blacks (1. 5). 5-year relative survival remained relatively unchanged over time in most racial/ethnic groups, except NH-Blacks experienced slight improvement (57% to 60%). In terms of histology, survival increased for endometrioid (87% to 89%) and non-endometrioid cases (54% to 58%) and decreased for sarcomas (46% to 42%). Conclusions: Early onset uterine cancer is rising in all women, and for both endometrioid and non-endometrioid subtypes. Of interest is the differences in the rates by histology when compared the full U. S. population: Among women aged 50 years, rates of uterine sarcomas were higher compared to non-endometrioid subtypes. These findings are concerning given that sarcomas are associated with poor prognosis and were the only cases to show decreased 5-year survival in our analysis. While rates of non-endometrioid subtypes are known to be higher among NH-Black women in the U. S. , we did not observe a striking racial difference among early onset cases. In fact, NH-Black women had the lowest rates of endometrioid and non-endometrioid subtypes, but highest rates of sarcomas compared to others. Next step for this analysis is hysterectomy correction, which, while expected to be relatively lower among women aged50 years, is known to vary by race/ethnicity. Citation Format: Akemi T. Wijayabahu, Megan A. Clarke. Early onset uterine corpus cancer incidence rates and 5-year relative survival by histologic subtype and race/ethnicity among women aged 20-49 years abstract. In: Proceedings of the AACR Special Conference on Endometrial Cancer: Transforming Care through Science; 2023 Nov 16-18; Boston, Massachusetts. Philadelphia (PA): AACR; Clin Cancer Res 2024;30 (5Suppl): Abstract nr B021.