In this study, the investigators aimed to apply their previously developed multi-locus blood-based assay targeting circulating tumor DNA methylation to monitor postoperative relapse and evaluate adjuvant chemotherapy efficacy in resected stage I and stage II (without high risk) colorectal cancer after radical resection.

This is a prospective, multicenter, observational, real-world study. Research objects: patients with surgically resectable colorectal cancer and ctDNA positive before surgery in stage I and stage II (without high risk). After giving fully informed consent, the participants will undergo the regular treatment according to NCCN guidelines. Serial analysis of ctDNA will be performed at specific time points including pre-treatment, postoperative week 3, postoperative 5 years ( every 3 months for the first 2 years, and every 6 months for the rest 3 years). Participants will be observed and examined during the follow-up period.

Inclusion Criteria:

• Patients must have histologically confirmed stage I/II (without high risk) colorectal cancer.
• Male or female ≥ 18 years of age on the day of signing informed consent.
• Patients need to receive surgical resection, and with ctDNA positive prior to resection of colorectal cancer (CRC).
• Patients must have a performance status of ≤1 on the Eastern Cooperative Oncology Group (ECOG) Performance Scale.
• 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:

• Personal history of colorectal cancer, colorectal adenoma or aerodigestive tract cancer.
• Induction of neoadjuvant systemic therapy prior to resection of CRC.
• Patient is pregnant or lactating.
• 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.
• Inadequate tumor material (either quality and quantity) to support circulating tumor DNA (ctDNA) analysis.

Patients 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. The written informed consent must be obtained from the patient prior to enrollment. The following criteria apply to all patients enrolled onto the study unless otherwise specified.