Neoadjuvant Low-dose Immunotherapy in Locally Advanced MMR-deficient Colorectal Cancer

Inclusion Criteria: * Availability of voluntarily signed informed consent from the patient * Histologically confirmed adenocarcinoma of the colon or rectum; * Locally advanced tumor - cT3-4N0-2M0 according to CT for tumors of the colon and sigmoid colon; cT3 with a depth of tissue invasion ≥5mm (cT2N0 and higher for lower ampullary cancer) or T4 or involvement of the lateral resection margins according to MRI for rectal cancer; * Presence of MSI/dMMR in the tumor; * ECOG 0-2; * No contraindications to surgical treatment of malignancy Exclusion Criteria: * Previous therapy with the inclusion of monoclonal antibodies - anti-PD1, anti-PD-L1, anti PD-L2, anti-CTLA4 antibodies and other immunotherapy drugs * The presence of any other malignant tumor, with the exception of radically treated basal cell carcinoma, cervical cancer in situ, currently or within 5 years before inclusion in the study * Pregnant and lactating women, as well as planning pregnancy during the period of therapy in a clinical trial and 6 months after the end of therapy * Patients with preserved reproductive potential who refuse to use adequate methods of contraception throughout the study and 6 months after the end of therapy or who agree to abstain from heterosexual contact. * Previous systemic therapy with immunosuppressive drugs (including, but not limited to: prednisone, cyclophosphamide, azathioprine, methotrexate, thalidomide and TNF \[tumor necrosis factor\] antagonists) within 4 weeks before signing …