Total Neoadjuvant Therapy and Organ Preservation Versus Surgery for Rectal Cancer.

Part One Inclusion Criteria: * Over 18 years of age. * Participants who agreed to participate in the study signed an informed consent form. * The Eastern Cooperative Oncology Group (ECOG) score ranges from 0 to 2. * Pathologically confirmed rectal adenocarcinoma. * Tumor up to 10 cm from the anus. * Magnetic resonance imaging (MRI) of the pelvis and computed tomography (CT) of the thorax and abdomen were performed to confirm the diagnosis. * cT1N1, T2-T3 N0 - 1, M0, MRF -, EMVI -. * Normal bone marrow function: blood leucocytes \> 3.5 × 10⁹/l, neutrophils \> 1.5 × 10⁹/l, platelets \> 100 × 10⁹/l. * Normal renal function: creatinine within 1,5 × normal. * Normal liver function: blood bilirubin levels within 1,5 times normal, AST, ALT levels within 2,5 times the upper limit. Exclusion Criteria: * Prior ST or Ch. * Participants who are not eligible for pelvic MRI. * Participants who have had a malignancy in the last 5 years, except for treatment for basal cell or squamous cell skin cancer or in situ cervical cancer. * ECOG status ≥ 3. * Distant metastases detected. * Participants with uncontrolled therapeutic or psychiatric conditions. * Infectious diseases requiring antibiotic treatment. Part Two Inclusion Criteria: * Over 18 years of age. * Participants who agreed to participate in the study signed an informed consent form. * ECOG score between 0 and 2. * Pathological confirmed rectal adenocarcinoma. * Stage I to III rectal cancer confirmed. * The tumor is localized up to 12 cm from the anus. * Participants who refused to participate in the first part of the study or did not meet the inclusion criteria for the first part. * Participants have received preoperative CRT or TNT or are in the planning stages of neoadjuvant treatment. Exclusion Criteria: * New cancer two years after CRT. * Stage IV cancer before treatment. * Participants refusing to participate in the study or unable to sign the informed consent.