This is a prospective diagnostic study. This study is to compare the performance between circulating tumor DNA (ctDNA) methylation and carcinoembryonic antigen (CEA) in detecting colorectal tumor. Firstly, based on the identification of differential ctDNA methylation biomarkers, the diagnostic model is established and the diagnostic performance was compared with that of CEA. Secondly, the stage stratification model was established preliminarily based on differential ctDNA methylation biomarkers and the performance was also compared with that of CEA.

Colorectal cancer (CRC) is the third most common cancer worldwide, the second deadliest cancer. It is reported that patients prefer non-invasive methods rather than invasive methods for the detection of CRC. Carcinoembryonic antigen (CEA) is commonly employed in clinical practice for early detection of CRC, but it is limited for its low sensitivity, which is around 30%-40%. DNA methylation is a commonly used biomarker for non-invasive tumor detection in plasma. We aim to develop and validate a ctDNA methylation-based blood test for CRC diagnosis based on genome-wide methylation detection. There are two steps in the study. Firstly, this prospective study aims to identify colorectal tumor differential circulating tumor DNA (ctDNA) methylation biomarkers, establish the diagnostic model. Secondly, we performed a preliminary study to stratify early-stage and advanced-stage disease based on the differential biomarkers.

Inclusion Criteria:

Case group

• Patients must have histologically confirmed colorectal cancer or advanced adenoma.
• Patients need to receive surgical resection or endoscopic resection.
• Patients have a performance status of ≤1 on the ECOG Performance Scale.
• Written informed consent must be obtained.

Control group

• Written informed consent must be obtained.
• Individuals must receive colonoscopy.

Exclusion Criteria:

• Patients received tumor treatment prior to the drawn of blood sample, including surgical resection, neoadjuvant chemoradiotherapy and targeted therapy.
• Patients received antibiotics regularly.
• Patients received blood transfusion two weeks before the drawn of blood sample.
• Patients with indications of emergency surgery, including bleeding, obstruction and perforation.
• Patients who are positive for Human Immunodeficiency Virus (HIV).
• Patients with abnormal liver and kidney function.
• Patients with the history of other malignancies, inflammatory bowel disease and Lynch syndrome.
• Patients who are pregnant or breastfeeding.
• Alcoholic or drug abusers.

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.

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