Participants: Patients who undergo radical treatment, including surgical R0 resection or achieve NED through local therapy after conversion therapy.

Interventions:

Conversion Therapy: Administered per standard clinical practice, with blood samples collected before and 3 - 6 weeks after for ctDNA, cfRNA, proteomics, and metabolomics analysis.

Surgery/Local Therapy: R0 resection or local therapy to achieve NED. Adjuvant Therapy: Given post - surgery based on clinical guidelines, with blood samples collected within 2 months post - treatment for MRD assessment.

Follow - up: 2 - year follow - up with imaging (CT/MRI) and tumor marker tests every 3 - 4 months to monitor recurrence.

Purpose: Evaluate the efficacy of conversion therapy and radical treatment in achieving tumor - free status and assess postoperative recurrence risk using MRD detection.

Participants: Patients who do not undergo radical resection or achieve NED after conversion therapy.

Interventions:

Conversion Therapy: Same as in Radical Treatment Group: Participants undergo plasma multi-omics detection (ctDNA, cfRNA, proteomics, and metabolomics) at the same time points to monitor disease progression and evaluate the effectiveness of non-radical treatment.

Description:

This study utilizes a holistic plasma multi-omics approach, integrating circulating tumor DNA (ctDNA), cell-free RNA (cfRNA), proteomics, and metabolomics to evaluate treatment response. Unlike conventional single-marker studies, this integration captures diverse biological signals-from genomic alterations to metabolic shifts-providing a superior assessment of efficacy and recurrence risk in oligometastatic CRC.

All participants, regardless of their subsequent treatment path (radical or non-radical), undergo standardized blood collection at key clinical milestones: baseline, post-conversion therapy, and throughout a 2-year follow-up period. This allows for a continuous molecular "snapshot" of the disease, enabling the identification of MRD-positive patients who may require intensified intervention.

The primary outcome is progression-free survival (PFS), stratified by minimal residual disease (MRD) status. PFS is defined as the time from treatment initiation to the first occurrence of tumor recurrence, disease progression, or death from any cause, whichever occurs first. Tumor assessments are performed every 3-4 months for up to 24 months using imaging (CT or MRI) and serum tumor markers (CEA and CA19-9). Blood samples are collected at predefined time points to determine MRD status via ctDNA analysis, which informs individualized treatment decisions. Differences in PFS between MRD-negative and MRD-positive groups are evaluated using the Kaplan-Meier method and log-rank test, with hazard ratios (HRs) and 95% confidence intervals (CIs) estimated using Cox proportional hazards regression.

Proportion of patients with tumor volume reduction ≥30% and maintained for ≥4 weeks, including complete response (CR) and partial response (PR).

Ability of ctDNA and cfRNA levels to predict treatment response and recurrence before imaging changes.