Molecular Classification and Clinical Outcomes in Endometrial Cancer: Real-World Evidence from a Tertiary Care Center

Background: Molecular classification has reshaped prognostication and treatment in endometrial carcinoma (EC). However, real-world evidence from Asian populations remains scarce. This study evaluated clinicopathologic characteristics and survival outcomes across molecular subtypes of EC in a Thai tertiary care center. Methods: This retrospective cohort included patients with histologically confirmed EC who underwent primary surgery at Chiang Mai University Hospital between 2015 and 2023, and had at least one investigation for molecular classification, including immunohistochemistry (IHC) for mismatch repair (MMR) proteins and p53, as well as POLE sequencing using the Idylla™ POLE-POLD1 Mutation Assay with confirmatory Sanger sequencing. Final molecular subtype assignment followed established hierarchical algorithms. Clinicopathologic variables were analyzed using Chi-square and logistic regression. Progression-free survival (PFS) and overall survival (OS) were estimated with Kaplan-Meier and compared using the log-rank test. Results: Among 803 EC cases diagnosed during the study period, 184 met the inclusion criteria. Of 184 patients, molecular subtypes were classified as POLE-mutated in 2.2%, dMMR in 38.6%, p53-abnormal (p53-abn) in 45.1% and NSMP (1.6%). dMMR tumors occurred predominantly in older women and exhibited mainly endometrioid histology, whereas p53-abn tumors were largely non-endometrioid and high-risk in the vast majority. In multivariate analysis, histologic type was the only independent predictor of both MMR deficiency (adjusted OR = 15.22; 95% CI 4.99-46.37; p < 0.001) and p53 abnormality (adjusted OR = 79.42; 95% CI 10.60-595.05; p = 0.003). Survival outcomes varied by molecular class: POLE-mutated tumors had excellent prognosis with no recurrence or death, dMMR tumors had intermediate outcomes, and p53-abn tumors showed the poorest PFS and OS. Overall survival differed significantly among subtypes. Conclusions: Molecular classification provides strong prognostic discrimination in EC, even with selective testing. MMR and p53 IHC serve as practical frontline tools, while POLE sequencing should be prioritized for intermediate- and high-risk endometrioid tumors. Expanded molecular testing in Asian populations is essential to refine risk stratification and optimize individualized management.