Prognostic Significance and Clinical Implications of the New FIGO 2023 Staging System in Patients with Endometrial Cancer

Background/Objectives: The 2023 revision of the International Federation of Gynecology and Obstetrics (FIGO) staging system redefines endometrial cancer staging by integrating histopathological and molecular parameters into conventional anatomic assessment. We aimed to quantify stage migration following reclassification from FIGO 2009 to FIGO 2023, to evaluate its impact on survival, and to identify independent prognostic determinants within this restaged cohort. Methods: In this two-center retrospective cohort study, 291 patients with histologically confirmed endometrial cancer were restaged according to both FIGO 2009 and FIGO 2023 systems. Progression-free survival (PFS) and overall survival (OS) were assessed using the Kaplan–Meier method, and independent prognostic determinants were identified through multivariable Cox proportional hazards modeling. Results: Application of FIGO 2023 resulted in stage migration in 32.0% of patients, with 30.6% upstaged and 1.4% downstaged. Upstaged patients demonstrated significantly worse PFS and OS compared with downstaged patients and patients without stage change (p < 0.001 for both). Notably, among patients initially classified as FIGO 2009 stage I, 38% were reassigned to a higher stage and exhibited a marked survival disadvantage (p < 0.001). In multivariable analysis, advanced age and positive surgical margins independently predicted both poorer PFS and OS, while lymphovascular space invasion (LVSI) independently predicted inferior PFS. The association with positive surgical margins, however, likely reflected concurrent advanced-stage disease. Conclusions: The FIGO 2023 staging system results in substantial stage redistribution in endometrial cancer and provides clearer survival discrimination, particularly by identifying previously unrecognized high-risk subgroups within early-stage disease. The significant survival disadvantage observed among upstaged patients indicates that the revised system may more accurately reflect biologically driven risk stratification. However, stage migration was not independently associated with survival after adjustment for its constituent pathological factors.