CD274 and hyperinsulinemic hypoglycemia, familial, 4: The MMR system corrects errors during DNA replication; MMR deficiency (dMMR) drives genomic instability and increased tumor mutational burden, and in endometrial cancers, dMMR status correlates with responsiveness to immunotherapy due to enhanced neoantigen presentation (17).While pMMR tumors typically show limited response to PD-1 monotherapy, approximately 60% of UCS express PD-L1, supporting exploration of combinatorial immunotherapies such as pembrolizumab plus Lenvatinib.