[Prognostic stratification value of MLH1 promoter methylation in endometrioid endometrial carcinomas with a dMMR molecular phenotype].

Objective: To investigate the prognostic stratification value of MLH1 promoter methylation in a mismatch repair deficiency (dMMR)-type endometrioid endometrial carcinoma (EEC). Methods: A total of 338 patients with confirmed diagnosis of dMMR EEC at Third Hospital of Peking University Health Science Center, from July 2005 to June 2023 were analyzed. Based on the promoter methylation, they were classified into a dMMR methylated (dMMR MET) group (177 cases) and a dMMR nonmethylated (dMMR nonMET) group (127 cases). Somatic mutations were analyzed by targeted sequencing (196/425-gene panel), and transcriptomic differences were assessed by RNA sequencing (Master panel). We compared the clinicopathological characteristics, gene mutation/expression profiles, and molecular pathway activities systematically between the two groups. Results: Compared with the dMMR nonMET group, patients of the dMMR MET group were older significantly [(56.89±8.85) vs. (53.76±9.45) years, P=0.003] and had tumor size of larger diameters [(3.39±1.78) vs. (2.71±1.31) cm, P=0.014]. The menopausal proportion (66.9% vs. 48.8%, P=0.002) and the proportion with tumor buddings (47.5% vs. 30.4%, P=0.036) were higher. No significant differences were identified in FIGO stage, histologic grade, depth of myometrial invasion, lymphovascular invasion, or rate of lymph node metastasis (P>0.05). Mutational profiling revealed that the nonMET group had significantly higher mutation frequencies in CHD4, NF1, SMARCA4, and RET (P<0.05). Transcriptomic analysis demonstrated upregulation of immune-related genes (CCL21, CXCL2) in the MET group, and downregulation of epithelial-mesenchymal transition (EMT)-associated genes (SOX2, FOXA1). Both GO and KEGG enrichment analyses of different gene expression in the MET group demonstrated an association with the MAPK pathway. However, Hallmark pathway analysis showed no significant differences in overall pathway activity between the two groups. Survival analysis revealed no significant differences in progression-free survival (P=0.206) or overall survival (P=0.813) between the groups. Conclusions: The methylation status of the MLH1 promoter has limited value in predicting the prognosis of dMMR EEC. Molecular pathways heterogeneity between the methylated and nonmethylated subgroups suggests the necessity of integrate multi-dimensional indicators to optimize stratification strategies, instead of relying on a single epigenetic marker.