Microsatellites act as „seismographs” of the genome

Short non-protein-coding repetitive regions consisting of 1-6 bp sequences are called microsatellites. Failure in DNA polymerase activity during replication may lead to an increase or reduction in the number of these repeats. Generally, these microsatellite number variations are corrected via the DNA repair machinery; if not, the alterations are transmitted to the progeny, which is also indicated by the elevated mutation rate in the offspring. Microsatellite instability (MSI) can also cause reading-frame problems, and this can lead to elevated expression of foreign antigens in tumors, promising an enhanced efficacy of the anti-tumour immune response. Thus, MSI indicates not only genetic instability but also an increased efficacy of immune checkpoint inhibitors. Various tools such as PCR-based techniques or immunohistochemical methods have been developed to confirm MSI and to examine the functionality of the DNA repair mechanisms in these patients. Additionally, the recent technology also allows us to examine of microsatellites by using next-generation sequencing or artificial intelligence-based image analysis methods. In this review, we summarize recent methodologies and the clinical significance of MSI analysis.