A Randomized Controlled Trial of Plasma ctDNA Methylation-Guided Adjuvant Chemotherapy Decision-Making in High-Risk Stage III (T4N+ or T1-3N2) Colorectal Cancer

Inclusion Criteria: 1. Age ≥18 years, regardless of sex; 2. Eastern Cooperative Oncology Group (ECOG) performance status of 0-2, with an expected survival of \>3 months; 3. Histologically confirmed postoperative pTNM stage high-risk stage II colorectal cancer; 4. Positive ctDNA status at 1 month after surgery; 5. Expected survival of \>12 months; 6. Ability to understand and willingness to sign a written informed consent form (personally or via a legally authorized representative/guardian), indicating that the subject understands the study objectives and required procedures and agrees to participate. Exclusion Criteria: 1. Receipt of neoadjuvant therapy prior to surgery; 2. Blood transfusion during surgery or within 2 weeks prior to surgery; 3. Pregnant or breastfeeding women, or individuals of reproductive potential who are not using adequate contraception; 4. History of other malignancies within the past 5 years, except for adequately treated carcinoma in situ of the cervix or non-melanoma skin cancer; 5. Uncontrolled primary brain tumors or central nervous system metastases, or presence of significant intracranial hypertension or neuropsychiatric symptoms; 6. Presence of severe or uncontrolled comorbidities, including but not limited to:Severe cardiac disease that remains unstable despite treatment, including myocardial infarction, congestive heart failure, unstable angina, symptomatic pericardial effusion, or unstable arrhythmia within 6 months prior to enrollment; Clearly diagnosed neurological or psychiatric disorders, including dementia or seizure disorders;Severe or uncontrolled infections;Active disseminated intravascular coagulation (DIC) or significant bleeding tendency;Significant impairment of major organ function; 7. Any other condition that, in the opinion of the investigator, would make the patient unsuitable for participation in this study.