Microsatellite instability (MSI) is caused by functional defects in DNA mismatch repair in tumor tissues. The new microsatellite alleles are present at a microsatellite locus in the tumor due to the insertion or deletion of duplicate units. MSI with DNA mismatch repair defects is an important clinical tumor marker. It is usually a result of defects in the mismatch repair (MMR) system, a group of enzymes responsible for monitoring and repairing the error incorporations in microsatellites. Here, we explored MSI subtype and its correlation with the immune environment in endometrial cancer. Using unbiased single-cell RNA-seq we found that the MSI tumors were associated with improved patient survival, the closer regulation of the immune environment, and MMR-D tumors showed a higher B cells infiltration. Our study analyzed the cell types in the endometrial cancer tumor microenvironment (TME). It elucidated the diverse functional phenotypes and states of malignant, T, and myeloid cell subsets to reveal the clinicopathological characteristics prognosis and immune microenvironment mapping in MSI-H/MMR-D endometrial carcinomas, thereby demonstrating the role of immune subsets in MSI and the relationship between immunotherapy and endometrial cancer.

Single-cell RNA-seq, Endometrial cancer microenvironment, Microsatellite instability (MSI), Mismatch repair (MMR), The tumor microenvironment (TME)