This observational study aims to assess the predictive value of postoperative circulating tumor DNA (ctDNA) monitoring in evaluating the risk of recurrence in stage I-IV colorectal cancer patients. The study involves the collection of blood samples from patients who have undergone surgery for colorectal cancer. Sensitivity-enhanced molecular biology techniques are utilized to detect ctDNA in these samples. The correlation between ctDNA detection and the risk of recurrence is evaluated by analyzing patient follow-up data and clinical information. The findings of this study may contribute to the development of improved postoperative management strategies, such as identifying high-risk individuals and implementing additional treatment measures to reduce the risk of recurrence.

Inclusion Criteria:

1. Age ≥ 18 years at the time of signing the informed consent form.

2. Eastern Cooperative Oncology Group (ECOG) Performance Status score of 0-1.

3. Histologically confirmed colorectal cancer located from the ileocecal junction to the rectosigmoid junction, with a distance of >15cm from the anal verge. Regardless of mismatch repair (MMR) status, Rat sarcoma (RAS) gene and proto-oncogene serine/threonine-protein kinase (RAF) gene status.

4. Pathologically or cytologically confirmed American Joint Committee on Cancer (AJCC) tumor node metastasis (TNM) stage I-IV colorectal cancer patients (8th edition).

5. No evidence of distant metastasis confirmed by comprehensive examination (no distant organ or lymph node metastasis).

6. Normal organ function, as indicated by the following criteria:

   • Hematology criteria: For patients who have not received blood transfusion, white blood cell (WBC) ≥ 3.5/4.0 × 10^9/L, neutrophils ≥ 1.5 × 10^9/L, platelet (PLT) ≥ 100 × 10^9/L.
   • Biochemistry criteria: Crea and bilirubin (BIL) ≤ 1.0 times the upper limit of normal (ULN), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 2.5 times ULN, alkaline phosphatase (ALP) ≤ 2.5 × ULN, total bilirubin (Tbil) ≤ 1.5 × ULN.

7. Ability to provide clinical data required for the study.

8. Sufficient tumor tissue available for analysis.

9. Patients capable of achieving R0 radical resection.

10. Patients capable of adhering to the planned schedule, actively participating in regular clinical follow-up, and necessary treatments.

Exclusion Criteria:

1. History of concurrent or prior malignancies (excluding adequately treated cervical carcinoma in situ, basal cell carcinoma, or squamous cell carcinoma of the skin).
2. Patients who have received neoadjuvant therapy.
3. Patients with other severe diseases that may affect follow-up and short-term survival, as determined by the investigator.
4. Any other medical, social, or psychological conditions that, in the opinion of the investigator, would make the patient unsuitable for participation in this study.
5. Inability to undergo clinical follow-up using contrast-enhanced magnetic resonance imaging (MRI) or contrast-enhanced computed tomography (CT).

Stage I-IV colorectal cancer with curative intent.