Prognostic and Clinicopathological Implications of Mismatch-Repair Deficiency and MLH1 Promoter Methylation Status in Endometrial Carcinoma

Objective: The prevalence of MSI-H and MLH1 promoter hypermethylation ( MLH1 -PHM) as well as Lynch syndrome in Japanese patients with endometrial cancer (EC) has not been fully revealed. There is also a recent report that the prognosis of MLH1 -PHM is worse than MLH1 non-PHM in EC; however, no large-scale studies have been conducted in Japan. We investigated the prevalence of MSI-H, MLH1 -PHM and Lynch syndrome in EC cases and characteristic and prognosis of them. Methods: The 677 patients who were pathologically diagnosed with EC at the Saitama Cancer Center Hospital between 2013 and 2023 were investigated in this study. The MSI and abnormal DNA methylation of the MLH1 promoter were tested in all cases. Patients with MSI-H EC or a family history provided informed consent and examined germline testing for Lynch syndrome. Results Among the 677 ECs, 170 (25.1%) were MSI-high (MSI-H), and 105 were involved MLH1 hypermethylation. Two of 13 Lynch syndrome cases had MLH1 -PHM in ECs. The MSI-H group had more G3 histology, but had a favorable prognosis with 5-year PFS and OS compared with the MSSgroup. The group with MLH1 -PHM have more patients with G1/2 histology and more advanced disease. There was no difference in prognosis between MLH1 -PHM and non-PHMgroups. Conclusion This study provides information on the prevalence of MIS-H and MLH1 -PHM in EC in Japan. Besides, the prognostic of MSI-H group is better than that in the MSSgroup, but no differences were found between the MLH1 -PHM and MLH1 non-PHM groups.