This is a prospective, multicenter, observational, single-blinded controlled study. Dynamic monitoring of patients with resectable colorectal cancer was performed using the previously established colorectal tumor-specific plasma ctDNA methylation markers (Multigene methylation detection). Dynamic monitoring of plasma ctDNA methylation before and after treatment and at regular follow-up in patients with colorectal cancer after radical resection of tumor, to explore the predictive effect of postoperative plasma ctDNA methylation on postoperative recurrence and whether dynamic monitoring of postoperative ctDNA methylation could be earlier than imaging examination to indicate tumor recurrence.

At present, the main treatment of colorectal cancer (CRC) is surgical resection. CRC patients after radical surgery have good overall survival. However, there are still a large number of patients with postoperative recurrence. The postoperative recurrence rate of stage II CRC patients is 20-30%, and that of stage III CRC patients is 50-60%. Currently, there is no effective measures to predict whether patients suffer postoperative relapse. Patients can only periodically visit doctors in the hope of timely treatment in case of recurrence. Current clinical monitoring methods mainly include imaging detection and tumor markers detection. However, long-term monitoring may affect patients' quality of life and increase patients' economic burden. Therefore, biomarkers that can predict the prognosis of patients and screen out those who need intensive follow up are urgently warranted. At present, imaging is the mainly used approach to monitor tumor recurrence. Quantitative determination of ctDNA methylation in plasma may find tumor recurrence trend before imaging detection, indicating that quantitative determination of ctDNA methylation in plasma is a more sensitive monitoring approach than traditional imaging detection. Can plasma ctDNA methylation be a new recurrence monitoring technique and prognostic prediction method of CRC in clinical practice? In this study, we aimed to monitor the dynamic level of plasma ctDNA methylation after surgery in CRC patients, and to explore the advantages of plasma ctDNA methylation detection over traditional CRC in recurrence monitoring and prognosis prediction. This is a prospective, multicenter, observational, single-blinded controlled study. Dynamic monitoring of CRC patients was performed using the previously established colorectal tumor-specific plasma ctDNA methylation markers. Dynamic monitoring of plasma ctDNA methylation before and after treatment and at regular follow-up in patients with CRC after radical resection of tumor, to explore the predictive effect of postoperative plasma ctDNA methylation on postoperative recurrence and whether dynamic monitoring of postoperative ctDNA methylation could be earlier than imaging examination to indicate tumor recurrence.

Inclusion Criteria:

• Male or female ≥ 18 years of age on the day of signing informed consent.
• Patients must have histologically confirmed colorectal cancer.
• Patients need to receive surgical resection.
• Patients must have a performance status of ≤1 on the ECOG Performance Scale.
• Life expectancy of more than 5 years.
• Written informed consent must be obtained from patient or patient's legal representative and ability for patient to comply with the requirements of the study.

Exclusion Criteria:

• Patients received adjuvant treatment prior to the surgical resection.
• Patients received blood transfusion two weeks before or during the surgical resection.
• Patients with unresected advanced colorectal adenoma.
• Patients who are positive for Human Immunodeficiency Virus (HIV), Hepatitis B or Hepatitis C.
• Patients who are pregnant.
• Patients who are alcoholic or drug abusers.
• Patients with a history or current evidence of any condition or abnormality that might confound the results of the study, interfere with the patient's participation for the full duration of the study, or is not in the best interest of the patient to participate, in the opinion of the Investigator.

Patients with resectable colorectal cancer must have baseline evaluations performed prior to the study and must meet all inclusion and exclusion criteria. In addition, the patient must be thoroughly informed about all aspects of the study, including the study visit schedule and required evaluations and all regulatory requirements for informed consent.