This study dynamically monitored the prognosis of stage I-IV colorectal cancer patients who could receive radical surgical resection by detecting the levels of polygene methylation in plasma samples from patients with colorectal cancer. In patients with colorectal cancer feasible radical surgery, plasma ctDNA methylation detection was performed before and after surgical treatment and during regular follow-up to explore the predictive effect of plasma ctDNA methylation status at different time points on postoperative recurrence. To explore whether postoperative dynamic monitoring of plasma ctDNA methylation can be used for adjuvant chemotherapy efficacy evaluation and whether it can indicate tumor recurrence and metastasis earlier than imaging examination.

1. Patients initially diagnosed with primary colorectal cancer were enrolled for screening, and plasma samples 1-2 days before radical bowel resection were collected for polygene methylation detection.
2. The postoperative follow-up was 2 years, and the reexamination included CT/MRI imaging assessment, blood CEA, and dynamic monitoring of plasma ctDNA methylation level. Blood samples were collected for 9 times.
3. Results analysis: To explore the application value of ctDNA methylation-MRD detection in the prediction of postoperative tumor recurrence risk after radical resection of colorectal cancer; The correlation between preoperative ctDNA methylation level and prognosis of early colorectal cancer.

Inclusion Criteria:

1. Newly diagnosed patients with primary colorectal cancer confirmed by histopathology (no restriction on histological type);
2. Patients diagnosed as stage I-III and feasible for radical bowel surgery;
3. Patients diagnosed by stage IV (only colorectal cancer patients with liver metastasis at the time of diagnosis) and feasible radical bowel resection or complete resection of liver metastasis;
4. No gender limitation, age ≥18;
5. ECOG score ≤1;
6. Life expectancy ≥5 years;
7. Those who fully understand the study and voluntarily sign the informed consent.

Exclusion Criteria:

1. Blood transfusion was performed during surgery or 2 weeks before surgery;
2. complicated with primary malignant tumors of other organs;
3. With colonic obstruction, intestinal perforation and other symptoms requiring emergency treatment;
4. Colorectal cancer was diagnosed with extrahepatic metastasis;
5. Neoadjuvant therapy (such as radiotherapy and chemotherapy) before radical bowel resection;
6. Radical bowel resection was performed after endoscopic surgery;
7. Concomitant symptoms and/or family history collection suggest hereditary colorectal cancer;
8. serious mental illness or drug abuse;
9. patients with serious heart, lung and vascular diseases who cannot tolerate surgery;
10. pregnant or lactating women;
11. Participate in other interventional clinical investigators within 3 months
12. Poor compliance, unable to complete the study according to the judgment of the researcher.

800 patients with initial clinical diagnosis of primary colorectal cancer