Prognostic and Predictive Values of Mismatch Repair Deficiency in Non-Metastatic Colorectal Cancer

SIMPLE SUMMARY: A subset of colorectal cancers (CRCs) displays deficient DNA mismatch repair (dMMR) that leads to microsatellite instability (MSI). These tumors have distinct clinicopathological features and have been associated with a more favorable prognosis. Knowledge of mismatch repair (MMR) status has important implications for disease diagnosis, surgical intervention, and adjuvant treatment decisions. ABSTRACT: Colorectal cancer (CRC) is the third most commonly diagnosed cancer worldwide. Universal MMR/MSI testing is standard of care for all patients with newly diagnosed CRC based on multi-society guidelines in the United States. Such testing is intended to identify patients with Lynch Syndrome due to a germline mutation in an MMR gene, but also detects those with sporadic dMMR/MSI-high CRCs. The prognostic utility of MMR/MSI status in non-metastatic colorectal cancer has been studied extensively, yet more limited data are available for its predictive utility. Results have not been entirely consistent due to potential stage-related differences and limited numbers of dMMR/MSI-H patients included in the studies. In this review, we summarize the current evidence for the prognostic and predictive value of dMMR/MSI-H in non-metastatic CRC, and discuss the use of this biomarker for patient management and treatment decisions in clinical practice.