The acquisition of genomic instability is one of the key characteristics of the cancer cell, and microsatellite instability (MSI) is an important segment of this phenomenon. This review aims to describe the mismatch DNA repair (MMR) system whose deficiency is responsible for MSI and discuss the cellular roles of MMR genes. Malfunctioning of the MMR repair pathway increases the mutational burden of specific cancers and is often involved in its etiology, sometimes as an influential bystander and sometimes as the main driving force. Detecting the presence of MSI has for a long time been an important part of clinical diagnostics, but has still not achieved its full potential. The MSI blueprints of specific tumors are useful for precize grading, evaluation of cancer chance and prognosis and to help us understand how and why therapy-resistant cancers arise. Furthermore, evidence indicates that MSI is an important predictive biomarker for the application of immunotherapy.

基因组不稳定性的获得是癌细胞的关键特征之一，微卫星不稳定性（MSI）是该现象的重要部分。这篇综述旨在描述失配导致MSI失配的DNA修复（MMR）系统，并讨论MMR基因的细胞作用。MMR修复途径的功能异常会增加特定癌症的突变负担，并且经常参与其病因学研究，有时作为有影响力的旁观者，有时作为主要推动力。长期以来，检测MSI的存在一直是临床诊断的重要组成部分，但仍未充分发挥其潜力。特定肿瘤的MSI蓝图可用于精确分级，评估癌症机会和预后，并帮助我们了解产生抗药性癌症的方式和原因。此外，证据表明MSI是免疫疗法应用的重要预测生物标志物。