Simplifying Mismatch Repair Deficiency Screening in Endometrial Adenocarcinoma: Immunohistochemistry with Two-Antibody Panel (PMS2 and MSH6).

Abstract

Mismatch repair deficiency (dMMR) is a well-established characteristic of endometrial adenocarcinoma and is crucial in screening for Lynch syndrome, guiding adjuvant treatment decisions, and identifying candidates for immune checkpoint inhibitors. The traditional approach to dMMR screening involves a four-antibody panel, but a simplified two-antibody method utilizing PMS2 and MSH6 has shown promise. This study aims to compare the diagnostic performance of the simplified two-antibody method with the traditional four-antibody panel in endometrial cancer samples. We conducted a retrospective cohort study on endometrial carcinoma cases diagnosed between 2013 and 2022. We compared the diagnostic performance of the two-antibody panel with the traditional four-antibody panel in detecting dMMR. Clinical data and immunohistochemistry results were collected, and agreement between the two methods was evaluated using Cohen's kappa coefficient. 304 endometrial cancer cases were included, with 27% demonstrating loss of at least one MMR protein using the four-antibody panel. The two-antibody method detected MMR deficiency in 26.6% of cases, with a high agreement rate of 98.8% between the two methods. Only one case showed discordant results, prompting further investigation. The simplified two-antibody MMR IHC screening approach using PMS2 and MSH6 showed high concordance with the traditional four-antibody panel. This suggests its potential as an alternative method for reflex MMR status testing in endometrial adenocarcinoma. The implementation of this approach could streamline the diagnostic process, reduce costs, and improve the detection of Lynch syndrome in affected individuals and their families. Further studies with larger cohorts and long-term follow-up are needed to validate these findings and assess the clinical implications of this approach in routine practice.