This study will utilize ctDNA methylation detection to evaluate patients with stage I or low-risk stage II colorectal cancer who are ctDNA-positive one month after surgery. It aims to investigate the impact of different adjuvant chemotherapy regimens on ctDNA clearance rates and their prognostic significance. By using postoperative ctDNA status to identify patients at high risk of recurrence, the study seeks to implement intensified chemotherapy strategies (treatment escalation) at an early stage, thereby improving ctDNA clearance and ultimately enhancing patient outcomes.

Inclusion Criteria:

Participants must meet all of the following 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; Any other condition that, in the opinion of the investigator, would make the patient unsuitable for participation in this study.