ctDNA as a Assisted Diagnosis, Early Intervention and Prognostic Marker for Peritoneal Metastases From Colorectal Cancer

Inclusion Criteria: * Patients must be a man or woman of at 18-75; * Patients must have an Eastern Cooperative Oncology Group (ECOG) Performance Status of 0-21； * Patients with primary colorectal cancer proven by pathology； * Patients with high risk factors for peritoneal metastasis (simultaneous peritoneal metastasis, ovarian metastasis, PT4, CT4, tumor perforation, tumor-complete intestinal obstruction, mucinous adenocarcinoma/signet ring cell carcinoma of PT3, positive surgical margin, and tumor rupture and hemorrhage); * 6-12 months after colorectal cancer radical surgery, patients who have two consecutive positive ctDNA tests within one month; * Patients who have finished standard adjuvant therapy after surgery; (Choose 5-FU or 5-FU analog-based chemotherapy regimen, and the perioperative chemotherapy should not exceed 6 months)； * Patients who are negative of recurrence or metastasis in conventional oncology examination (serology, endoscopy, imaging) ; * Written informed consent must be obtained from patients and ability for patients to comply with the requirements of the study. Exclusion Criteria: * Patients who were diagnosed with other malignant tumors within 2 years before diagnosis of colorectal cancer; * ASA class Ⅳ to Ⅴ; * Patients who have other existence of distant metastasis outside the abdomen; * Patients with serious mental illness; * Patients with severe cardiovascular disease, uncontrollable infections, or other uncontrollable co-diseases; * Patients wh…