CAPEOX vs Observation in Colorectal Cancer Patients With Positive MRD

Inclusion Criteria: 1. Colorectal cancer confirmed by pathology, and the TNM stage (AJCC v8) is stage I or stage II. Stage II patients have T3 colonic adenocarcinoma with proficient mismatch-repair system (by immunohistochemistry for four mismatch repair proteins MSH1, MSH2, MSH6, and PMS2) and have no the following clinical risk factors: a) less than 12 lymph nodes examined; b) mucinous carcinoma; c) poor differentiation; d) bowel obstruction or perforation; e) lymphatic/vascular invasion, perineural invasion; f) close, indeterminate, uncertain, positive margins 2. ECOG performance status 0-1 3. No neoadjuvant therapy before surgery 4. Appropriate for active surveillance (i.e., no adjuvant chemotherapy) based on current practice patterns or according to the Chinese Society of Clinical Oncology guidelines for Colorectal Cancer (version 2022) 5. No history of other primary cancers in the past 3 years 6. No history of bone marrow, stem cell or organ transplant 7. Blood samples from 7 to 21 days after surgery were tested positive for ctDNA (tested by MinerVa MRD assay) 8. Pregnancy test done within 14 days before randomization must be negative (for women of childbearing potential only) 9. Voluntarily join the study and sign the informed consent document 10. No unstable or any medical condition that affects patient safety and study compliance evaluated by researchers 11. Availability and provision of adequate surgical tumor tissue for molecular diagnostics Exclusion Criteria: 1. Patients with multiple primary colorectal cancers 2. Patients with another primary cancer 3. Patients have the following conditions by blood test, or have obvious contraindication in adjuvant chemotherapy: 1. Moderate/severe renal impairment (GFR\<30 ml/min), as calculated by the Cockcroft and Gault equation 2. Absolute neutrophil count \<1.5×109/L 3. Platelet count \< 75×109/L 4. Hemoglobin \<90 g/L 5. Aspartate aminotransferase/Alanine aminotransferase \>2.5 × upper limit of normal 4. Lactating women 5. Have serious or uncontrolled medical condition that may preclude compliance with the protocol