The purpose of this study was to observe the relationship between ctDNA as a molecular marker of colorectal cancer and the risk of postoperative recurrence.

In this clinical study, ctDNA will be detected in postoperative patients with stage Ⅱ and Ⅲ colorectal cancer to evaluate the correlation between ctDNA and the risk of postoperative recurrence. According to the dynamic changes of ctDNA after adjuvant chemotherapy, the correlation between ctDNA and postoperative DFS will be compared, and the feasibility of ctDNA as a molecular marker to evaluate the risk of postoperative recurrence of colorectal cancer will be investigated.

Inclusion Criteria:

• 1. Patients with colorectal cancer diagnosed pathologically as stage Ⅱ and stage Ⅲ.
• 2. The patient underwent radical surgical treatment.
• 3. The patient has the results of genetic genetic testing for gastrointestinal tumors, including the genetic mutation status of MMR genes and related genes (MLH1, MSH2, MSH6, PMS2, MLH3, EPCAM).
• 4. The patient understands and is willing to sign a written informed consent document.
• 5. During the treatment process, the patient can cooperate to provide samples of each node.
• 6. The patient can provide corresponding clinical materials, including but not limited to case diagnosis, imaging evaluation, and serum protein marker test results.

Exclusion Criteria:

• 1. The patient cannot provide a complete and qualified specimen.
• 2. The patient has other primary malignant tumors or serious medical illnesses.
• 3. The patient cannot cooperate with the follow-up.
• 4. Conditions that other researchers deemed inappropriate for continuing to participate in the study.