Introduction/Background Tumour testing for DNA mismatch repair (MMR) is recommended for all endometrial cancers (EC) and is incorporated into the new molecular classification. This study aimed to find the prevalence of MMR deficiency (dMMR), Lynch Syndrome (LS), and to evaluate the differences in prognostically important clinicopathologic features between MMR proficient (pMMR) and dMMR among Indian EC patients.

Methodology Clinical and pathologic information of women treated for EC between 2019–2020 were obtained from electronic medical records. Fisher exact test was used for comparison of categorical variables. Survival analysis was done using Kaplan-Meier method and Cox Proportional Hazards model.

Results Over 2 years 108 EC tumour testing was done and 24% (26 pts) were dMMR by immunohistochemistry. Frequencies of MMR loss of expression were: MLH1/PMS2 loss in 14, MSH2/MSH6 loss in 5, MSH6 loss in 5, and PMS2 loss in 2. Six patients (5.6%) had germline mutations suggestive of LS with 2 (1.9%) among them having positive family history. Stage at diagnosis did not differ significantly between dMMR and pMMR. Lymphovascular invasion (LVI) (p = 0.003), and grade 2–3 (p = 0.002) were significantly more frequent in the dMMR group. Two-year recurrence-free survival (RFS) in pMMR and dMMR groups were 86% and 91% (p=0.8) respectively, while median RFS was not reached in either group.

Conclusion Almost one in four EC tumours is dMMR, with higher MMR reflexed detection of LS than by family history criteria. Higher grade and LVI were more common in dMMR but short-term outcomes were similar in dMMR and pMMR.