The goal of this clinical trial is to explore the predictive effect of postoperative plasma ctDNA methylation status on postoperative recurrence free survival (RFS) of colorectal cancer patients with peritoneal metastasis after R0/R1 resection. The main questions it aims to answer are:

Preoperative and postoperative plasma ctDNA methylation detection (ColonAiQ) was performed in patients with peritoneal metastasis from colorectal cancer who underwent R0/R1 resection. Clinical information of patients was collected to explore the predictive effect of postoperative plasma ctDNA methylation status on postoperative recurrence free survival (RFS) of colorectal cancer patients with peritoneal metastasis.

Participants will:

The patients were followed up according to the normal review procedure of the hospital and the NCCN guidelines until at least 24 months after surgery. The review content included CT/MRI imaging evaluation and blood CEA (every 3 months). Whole-blood samples were obtained for timely plasma separation and ctDNA extraction at 1 month after surgery (before the start of postoperative chemotherapy) and every 3 months through 24 months after surgery. One blood sample was obtained when tumor recurrence was first detected on imaging.

Detection of methylation in tissue and plasma samples

1. GutSeer methylation NGS was performed on peritoneal metastatic cancer tissues and paired normal peritoneal tissues.
2. ctDNA GutSeer methylation NGS was performed on plasma samples before surgery, 1 month after surgery, 24 months after surgery, and when tumor recurrence was first detected by imaging examination.
3. ctDNA methylation PCR (ColonAiQ) was performed on plasma samples before surgery, 1 month after surgery, every 3 months to 24 months after surgery, and when tumor recurrence was first detected by imaging examination.

Inclusion Criteria:

-1. No gender limit, age greater than 18 years old; 2, ECOG score ≤1; 3. Life expectancy ≥2 years; 4. Colorectal adenocarcinoma/mucinous adenocarcinoma/signet ring cell carcinoma confirmed by histopathology; 5, preoperative PCI score ≤20, peritoneal tumor cytoreductive surgery (CRS), surgery to achieve R0/1 resection; 6. Be able to understand the situation of this study and sign the informed consent.

7. The primary colorectal cancer has undergone R0 resection, and there is no extraperitoneal metastasis (except ovary).

Exclusion Criteria:

• 1. Combined with primary malignant tumors of other organs (current or within the past 5 years) (excluding patients with skin basal cell carcinoma and cervical carcinoma in situ undergoing radical treatment); 2. Severe mental illness or drug abuse; 3, severe heart, lung, vascular disease can not tolerate surgery; 4. Pregnant or lactating women.

Patients with peritoneal metastasis from colorectal cancer whose preoperative imaging PCI score was ≤20 and could be evaluated for R0/R1 resection were screened for enrollment. Preoperative plasma samples and tumor tissue samples were collected for ctDNA multigene methylation markers detection. Patients who achieved R0/R1 resection of peritoneal carcinomatosis were enrolled in this clinical study.

The results of clinical trials will be published in the form of a paper, but content involving patient personal information or sensitive information will be kept confidential as required by the Ethics Committee