Microsatellite instability (MSI) is a marker of the replication error phenotype. It is caused by impaired DNA mismatch repair processes (MMR), resulting in ineffectiveness of the mechanisms responsible for the DNA replication precision and postreplicative DNA repair. MSI underlies the pathogenesis of 10%-20% of colorectal cancer (CRC) cases. The data about the potential value of MMR status as a predictive factor for 5-fluorouracil (FU)-based chemotherapy remain unclear. According to National Comprehensive Cancer Network updated guidelines, MSI testing is recommended for all patients with stage II CRC because patients with MSI-H (high-frequency MSI) tumour may have a good prognosis and obtain no benefit from 5-FU-based adjuvant chemotherapy. The significance of the MSI status as a predictive factor for patients with metastatic disease was not confirmed. The association between the MSI status and the efficacy of the therapy based on anti-programmed death-1 receptor inhibitors requires further studies.
Keywords: colorectal cancer; microsatellite instability; mismatch repair.