MRD-Guided Surveillance in Locally Advanced Mid-Low Rectal Cancer (SURVEILLANCE-III)

This is a multicenter, prospective, observational study designed to evaluate the effectiveness of ctDNA-based MRD monitoring in predicting disease recurrence and survival outcomes in patients with locally advanced mid-low rectal cancer. The study will enroll 139 patients who have not previously received chemotherapy, radiotherapy, or targeted therapy. Key Objectives Primary Objective: To explore the correlation between MRD status and disease-free survival (DFS) in locally advanced mid-low rectal cancer patients. Secondary Objectives: To assess the relationship between MRD status and 1-year/2-year recurrence-free survival (1yRFS, 2yRFS). To evaluate the association between MRD status and overall survival (OS). Exploratory Objectives: To determine the average time by which MRD detection precedes imaging-based detection of disease recurrence. To assess the correlation between post-neoadjuvant therapy MRD status and pathological complete response (pCR). Study Design Patients will undergo blood sampling at key time points: Baseline (pre-neoadjuvant therapy) Pre-surgery (0-7 days before surgery) Post-surgery (7±2 days after surgery) Follow-up visits at 1, 3, 6, 9, 12, 18, 24, and 36 months post-surgery MRD status will be assessed using a ctDNA methylation-based PCR test, which provides a rapid, cost-effective alternative to traditional NGS-based methods. Statistical Analysis Kaplan-Meier survival analysis will be used to estimate DFS, RFS, and OS. Cox proportional hazards models will assess whether MRD status serves as an independent prognostic factor for recurrence. Multivariate analysis will adjust for clinical variables, including tumor burden and treatment history. Ethical Considerations The study adheres to the principles of the Declaration of Helsinki and Chinese Good Clinical Practice (GCP) guidelines. Informed consent will be obtained from all participants, and privacy and confidentiality will be strictly maintained. Expected Outcomes This study aims to validate the clinical utility of ctDNA-based MRD monitoring in predicting recurrence and survival outcomes for locally advanced mid-low rectal cancer patients. If successful, MRD testing may offer a more effective tool for postoperative surveillance and treatment planning, allowing for earlier interventions and improved long-term outcomes.