This prospective study (PMEIRR-OCCCT) evaluates the utility of plasma multi-omics-including circulating tumor DNA (ctDNA), cell-free RNA (cfRNA), proteomics, and metabolomics-in assessing response to conversion therapy and predicting recurrence in 120 patients with oligometastatic colorectal cancer (≤5 liver and/or lung metastases). Blood samples are collected at predefined timepoints: before conversion therapy, 3-6 weeks post-therapy, within 2 months after surgery or non-radical treatment, and during 24-month follow-up. Patients are stratified into radical vs. non-radical treatment groups based on post-conversion resectability. Tumor assessments (CT/MRI and CEA/CA19-9) occur every 3-4 months. The primary endpoint is progression-free survival (PFS) stratified by MRD status (ctDNA-negative vs. ctDNA-positive). Secondary endpoints include objective response rate (ORR), overall survival (OS), and duration of no evidence of disease (NED). The study aims to identify multi-omic biomarkers for early recurrence prediction and personalized intervention.