Expression of Programmed Cell Death Ligand-1 and Mismatch Repair Status in Endometrial Carcinomas

Background and Aims: Programmed death ligand-1 (PD-L1) is a co-regulatory molecule that suppresses local immunity, and mismatch repair (MMR) deficiency (dMMR) is reported to influence the response to anti-PD-L1-targeted therapy. This study was conducted to find the PD-L1 status, the occurrence of dMMR in endometrial carcinomas, and the association between them. Materials and Methods: The study included 35 resected specimens of endometrial carcinomas represented on formalin-fixed paraffin-embedded sections from January 2016 to July 2020. The clinicopathologic information including patient age, tumor histologic type, grade, stage, lymphovascular invasion, the extent of myometrial invasion, and the percentage of tumor-infiltrating lymphocytes (TILs) were obtained in all cases. The expression of PD-L1 and MMR antibodies including mutS homolog 2 (MSH-2), MSH-6, mutL homolog 1 (MLH-1) and MLH-3, and postmeiotic segregation 2 were assessed using immunohistochemistry. The statistical analysis was done using the Statistical Package for the Social Sciences (SPSS) version 26. Results: PD-L1 expression was noted in 48.6% of the cases in tumor cells and 65.7% of the cases in TILs and MMR was deficient in 28.6% of endometrial carcinomas. A statistically significant relation was noted between dMMR and TILs, PD-L1 expression in tumor cells and TILs, PD-L1 expression in tumor cells, and extent of myometrial invasion. Although there was no statistically significant association between MMR status and PD-L1 expression in tumor cells or TILs, 60% of patients with dMMR were PD-L1 positive. Conclusion: Sixty percent of dMMR cases showed PD-L1 expression in tumor cells. We conclude, ECs that are MMR deficient might get better response to anti-PD-L1 therapy. This study also revealed the prognostic use of TILs in PD-L1-expressed tumors.