Mismatch Repair (MMR) Protein Deficiency in Endometrioid Endometrial Carcinoma: Is There a Survival Impact?

Aim: This study aimed to investigate the prognostic significance of mismatch repair (MMR) protein deficiency in patients with endometrioid endometrial carcinoma (EEC). Material and Methods: A total of 201 EEC cases diagnosed between 2011 and 2025 were retrospectively analyzed. Immunohistochemistry was performed to assess the expression of MMR proteins (MLH1, PMS2, MSH2, MSH6), classifying tumors as deficient (dMMR) or proficient (pMMR). Survival outcomes were assessed, and the associations of MMR status with overall survival (OS), progression-free survival (PFS), and clinicopathological parameters were investigated, while the impact of specific histopathological features such as histological grade and serosal involvement on OS and PFS was evaluated. Results: Among the cases, 32.3% (n=65) were classified as dMMR. Although dMMR cases had slightly shorter OS and PFS than pMMR cases, the differences were not statistically significant (p=0.514 and p=0.309, respectively). In multivariate analysis, serosal involvement, high-grade histology, age ≥60 years, and tumor invasion depth ≥2 cm independently predicted poorer OS, while serosal involvement and high-grade histology independently predicted shorter PFS. dMMR showed significant associations with higher histological grade, cervical stromal invasion, serosal involvement, high Ki-67 index, and advanced stage. Conclusion: While MMR deficiency did not show a significant impact on survival, it was associated with adverse pathological features, suggesting a more aggressive tumor phenotype. These findings support further investigation into the role of MMR status in risk stratification and therapeutic decision-making in EEC.