Introduction/Background An increased incidence of endometrial cancer (EC) has been noted worldwide, especially in premenopausal women in countries with rapid socioeconomic transition. This study aims to examine tumour and patient’s characteristics and prognosis in premenopausal women with EC by combining validated Swedish registries.

Methodology The study population includes women ≤50 years with EC, included in the Swedish Quality Register Gynaecological Cancer 2010–2021. Register data was manually completed with data from medical records. Cox regression models were used to analyse factors associated with disease-free survival (DFS).

Results The study cohort consisted of 797 women ≤50 years (5%) out of 15902 patients with EC. Only 138 patients (0.9%) were <40 years of age. The majority of patients (n=757, 95%) had endometrioid EC and 40 patients (5%) non-endometrioid EC. The 5-year DFS for the study cohort was 90% (endometrioid 91%, non-endometrioid 65%, FIGO I/II 94%, FIGO III/IV 70% respectively). Women with BMI ≥30 had a higher DFS (94%) compared to women with BMI<30 (87%), p=0.0024. Multivariable analyses showed that factors associated with lower 5-year DFS were non-endometrioid histology, HR (hazard ratio) 3.66 (95% CI 1.81–7.39), FIGO stage III, HR 4.47 (95% CI 2.05 -9.76) and IV, HR 21,17 (95% CI 9.82–45.61). Women with BMI 30–39 had an improved DFS, HR 0.26 (95% CI 0.11–0.65) compared to women with both lower and higher BMI. Use of MHT did not increase the risk of recurrence adjusted HR 0.51 ( 95% CI 0.16–1.67).

Conclusion In this nationwide large cohort study we could demonstrate that, in general, premenopausal women with EC have good prognosis and non-endometrioid EC is rare in this group. Women with obesity (BMI 30–39) had a pronounced decreased risk for recurrence or death than women with lower or higher weight. This may indicate that this group may develop less aggressive EC or that overweight has a protective effect.

Disclosures None.