Clinicopathologic characteristics and cancer-specific survival in adolescents and young adults with endometrial cancer: A population-based SEER analysis.

e17615 Background: Endometrial cancer is the most common gynecologic malignancy in the United States, with an increasing incidence among younger women. Adolescents and young adults (AYAs) represent a distinct population with differing tumor biology, treatment patterns, and survivorship considerations compared with older adults. We evaluated age-based differences in presentation, treatment utilization, and CSS among patients with endometrial cancer. Methods: We conducted a retrospective population-based study using Surveillance, Epidemiology, and End Results (SEER) Research data (17 registries; diagnoses 2000–2022; November 2024 submission). Women with primary endometrial cancer were identified using ICD-O-3 site codes. AYAs were defined as age <40 years and compared with older adults (≥40 years). Variables included stage, histology, grade, race, year of diagnosis, and receipt of surgery. Descriptive comparisons used chi-square testing. CSS was estimated using the Kaplan–Meier method and compared using the log-rank test. Multivariable Cox regression identified independent predictors of CSS. Analyses were performed using Stata/SE 19.5. Results: Among 279,829 women with endometrial cancer, 10,711 (3.8%) were AYAs. Median age was 35 years (IQR 32–38) in AYAs and 63 years (IQR 55–71) in older adults. AYAs more frequently presented with localized disease (52.3% vs 48.4%) and less often with regional (10.1% vs 14.6%) or distant disease (4.6% vs 6.4%). Endometrioid histology predominated in both groups but was more common in AYAs (68.3% vs 63.2%), whereas non-endometrioid tumors were markedly less frequent (2.1% vs 14.0%). High-grade disease occurred less often in AYAs (7.6% vs 17.1%). AYAs had lower proportions of non-Hispanic White patients (71.2% vs 80.0%) and higher representation of Asian/Pacific Islander patients (15.1% vs 8.6%). Surgery was performed less frequently in AYAs (82.5% vs 90.3%). Median CSS was not reached among AYAs, while older adults experienced significantly inferior CSS (p<0.001). On multivariable analysis, AYA status was independently associated with improved CSS (HR 0.39, 95% CI 0.36–0.43). Advanced stage, non-endometrioid histology, high-grade disease, Black race, and lack of surgery were independently associated with worse CSS (all p<0.001). Conclusions: In this extensive population-based analysis, adolescents and young adults with endometrial cancer demonstrated significantly more favorable cancer-specific survival compared with older adults. Across all ages, advanced stage, non-endometrioid histology, high-grade disease, Black race, and lack of surgery were independently associated with worse survival. These findings underscore important age- and race-based disparities and highlight the need for tailored management and survivorship strategies in younger patients.