Blood and tumor samples will be obtained from enrolled patients. 4 ml of venous blood samples will be taken into a tube with EDTA and stored at -20 0C. Tumor samples will be taken during endoscopy or surgical treatment, embedded in paraffin and stored at room temperature.~Microsatellite instability in the tumor tissue will be determined by any method available in the participating center (immunohistochemical or molecular genetic study). In case of detection of microsatellite instability/deficiency in the repair system of unpaired bases blood samples will be analyzed for the fact that germinal mutations in the DNA mismatch repair genes.~Patients will be followed up for 5 years after enrollment. During follow up correlation of spectrum of germinal mutations with clinical data, effectiveness of therapy with immune checkpoint inhibitors, the spectrum of malignant neoplasms in the families of patients with Lynch syndrome, the impact of the presence of microsatellite instability/deficiency in the DNA mismatch repair genes on treatment tactics in the Russian Federation will be assessed.
Prospective multicenter registry study to assess the frequency of Lynch syndrome among patients with colorectal cancer in Russia