Abstract IA008: Mismatch repair deficiency and survival in stage I endometrial cancer

Abstract The importance of testing for DNA mismatch repair defects and high levels of tumor microsatellite instability (MSI) is established for screening colorectal and endometrial cancers for Lynch Syndrome and advanced solid tumor malignancies for treatment with checkpoint inhibitors. Therefore, accurate clinical assays are necessary to identify DNA mismatch repair defects and patients with cancers with high levels of MSI. While defects in DNA mismatch repair identified by immunohistochemistry may often overlap with tumor microsatellite instability as identified by PCR-based assays, the two molecular events are not synonymous and can be discordant in individual cancers. Cancers outside of the GI tract may have loss of DNA mismatch repair proteins but may have more subtle microsatellite instability or even be microsatellite stable. The College of American Pathologists has established an expert guideline committee to help navigate some of the clinical testing issues when trying to detect defects in DNA mismatch repair and MSI in cancers. In addition to these established clinical uses of DNA mismatch repair and MSI, their use as a prognostic biomarker for endometrial cancer is emerging. Data suggest that specific environmental factors may interact with DNA mismatch repair, causing a more variable phenotype in cancers with loss of DNA mismatch repair. Citation Format: Russell R. Broaddus. Mismatch repair deficiency and survival in stage I endometrial cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference: Endometrial Cancer: New Biology Driving Research and Treatment; 2020 Nov 9-10. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(3_Suppl):Abstract nr IA008.