Introduction. The emergence of new markers that determine the choice of therapy for metastatic colorectal cancer (CRC) has led to an increase in overall survival. The optimal treatment tactics now take into account both clinical and molecular-genetic characteristics of the tumor.Aim. Investigation of the features of the KRAS, NRAS and BRAF mutations and amplification of the HER2 gene depending on microsatellite instability (MSI) in CRC.Materials and methods. The study included 400 patients with CRC. MSI, BRAF V600E mutation, mutations in the KRAS and NRAS genes was identified to them. MSI was determined by fragment analysis, and mutations in the KRAS, NRAS, BRAF genes by realtime PCR. HER2 amplification was determined in 100 patients with a negative RAS/BRAF. NTRK translocations were determined in all patients with MSI. Data on preoperative levels of CEA and CA19-9 were obtained from 185 patients.Results and discussion. The prevalence of MSI was 6.8%. The prevalence of KRAS, NRAS, BRAF mutations in CRC with MSI was 66.7%, and in CRC with MSS - 52.3%. In patients with MSI, the level of CEA was lower than in MSS (p = 0.0061). The overall prevalence of KRAS and NRAS mutations was 45% and 2.5%. The overall prevalence of the BRAF V600E mutation was 5.8% and was more common in MSI-positive tumors (p < 0.0001). Regardless of MSI, BRAF-positive tumors were characterized by right-sided localization (p < 0.0001), category T3-4 (p = 0.013), lymph node involvement (p = 0.004), carcinomatosis (p = 0.046), high levels of CA19-9 (p = 0.014). HER2 amplification was found in 7% of wild-type RAS/BRAF cases and was associated with rectal cancer (p = 0.044), category T3-4 (p = 0.041), and distant metastases (p = 0.038). HER2 amplifications and NTRK translocations were not detected in cases with MSI.Conclusion. MSI-positive CRC had a higher prevalence of mutations in major genes. CRC with the BRAF V600E mutation and HER2 amplification had aggressive clinical and morphological parameters.
