• Cohort A:

• Rectal cancer patients who have previously received perioperative XELOX regimen treatment.

• Cohort B:

⁃ Signed written informed consent prior to any trial-related procedures;

⁃ Non-bedridden cases, regardless of gender, aged 18-75 years;

⁃ Pathologically confirmed rectal adenocarcinoma, excluding anal squamous cell carcinoma;

⁃ No prior antitumor treatment for rectal cancer. For those with Lynch syndrome, no antitumor treatment has been administered for the colorectal cancer related to this diagnosis;

⁃ Based on high-resolution MRI, classified as T1-3bN1-2 or T3aN0 or T3bN0; no involvement of the levator ani muscle; negative mesorectal fascia (MRF) status; negative extramural vascular invasion (EMVI); no cancerous nodules;

⁃ ECOG performance status of 0-1;

⁃ Expected survival time \> 3 months;

⁃ Adequate organ function, with subjects meeting the following laboratory criteria:

⁃ Absolute neutrophil count (ANC) ≥ 1.5 x 10\^9/L without using granulocyte colony-stimulating factor in the past 14 days.

⁃ Platelet count ≥ 100 x 10\^9/L without transfusion in the past 14 days.

⁃ Hemoglobin \> 9 g/dL without transfusion or use of erythropoietin in the past 14 days;

⁃ Total bilirubin ≤ 1.5 × upper limit of normal (ULN); if total bilirubin \> 1.5 × ULN but direct bilirubin ≤ ULN, enrollment is also allowed;

⁃ Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 2.5 × ULN (patients with liver metastases are allowed if ALT or AST ≤ 5 × ULN);

⁃ Serum creatinine ≤ 1.5 × ULN and creatinine clearance (calculated by the Cockcroft-Gault formula) ≥ 60 ml/min;

⁃ Good coagulation function, defined as an international normalized ratio (INR) or prothrombin time (PT) ≤ 1.5 × ULN;

⁃ Normal thyroid function, defined as thyroid-stimulating hormone (TSH) within normal range. If baseline TSH is outside the normal range, subjects can still be enrolled if total T3 (or FT3) and FT4 are within normal range;

⁃ Normal levels of cardiac enzyme profile (subjects may still be enrolled if the investigator judges the laboratory abnormality to be of no clinical significance); (optional)

‣ For female subjects of childbearing potential, a urine or serum pregnancy test must be performed within 3 days prior to the first dose of the investigational drug (Day 1 of Cycle 1) with a negative result. If the urine pregnancy test result cannot be confirmed as negative, a blood pregnancy test is required. Non-childbearing potential females are defined as those who have been postmenopausal for at least one year, or have undergone surgical sterilization or hysterectomy;

∙ If there is a risk of conception, all subjects (regardless of gender) must use contraception with a failure rate of less than 1% throughout the treatment period and until 120 days after the last dose of the investigational drug (or 180 days after the last dose of chemotherapy).