检测错配修复缺陷（dMMR）和高级别微卫星不稳定（MSI-H）已成为结直肠癌（CRC）常规诊断工作的重要组成部分。虽然MSI最初被认为是癌症遗传易感性（Lynch综合征，LS）的可能指标，但如今重点在于预测对免疫检查点抑制剂（ICI）的治疗反应。在初诊中可以使用对应的建议和测试算法（参见：Rüschoff等人，2021）。考虑到ICI治疗在非CRC中，如子宫内膜癌、小肠癌、胃癌和胆道癌等方面所扮演的角色不断扩大，本文对dMMR/MSI测试进行了更新的评述。重点在于评估免疫组化染色的挑战和PCR-based程序的价值，考虑到扩大的ICI适应症范围。提供了面向日常诊断决策的实践导向流程图，考虑了MMR-IHC和MSI-PCR结果间不一致的频率和类型的新数据，以及下一代测序在澄清这些不一致性中的可能作用。强调了系统质量保证措施的重要性（例如QuIP MSI门户网站和多中心熟练性测试），包括定期继续培训和教育。© 2023. 作者。

Testing to detect mismatch repair deficiency (dMMR) and high-grade microsatellite instability (MSI-H) has become an integral part of the routine diagnostic workup for colorectal cancer (CRC). While MSI was initially considered to be a possible indicator of a hereditary disposition to cancer (Lynch syndrome, LS), today the prediction of the therapy response to immune checkpoint inhibitors (ICI) is in the foreground. Corresponding recommendations and testing algorithms are available for use in primary diagnosis (reviewed in: Rüschoff et al. 2021).Given the increasing importance for routine use and the expanding indication spectrum of ICI therapies for non-CRCs, such as endometrial, small intestinal, gastric, and biliary tract cancers, an updated review of dMMR/MSI testing is presented. The focus is on the challenges in the assessment of immunohistochemical stains and the value of PCR-based procedures, considering the expanded ICI indication spectrum. A practice-oriented flowchart for everyday diagnostic decision-making is provided that considers new data on the frequency and type of discordances between MMR-IHC and MSI-PCR findings, and the possible role of Next Generation Sequencing in clarifying them. Reference is made to the significance of systematic quality assurance measures (e.g., QuIP MSI portal and multicenter proficiency testing), including regular continued training and education.© 2023. The Author(s).