The goal of this study is to evaluate the efficacy and safety of multi-mode ablation combined with systemic therapy including PD-1(programmed death receptor 1) inhibitor for colorectal cancer liver metastasis and furthermore to clarify its application value by comparing preoperative and postoperative immune indicators.

This is a single-center, single-arm, prospective study to evaluate the efficacy and safety of multi-mode ablation combined with systemic therapy including PD-1 inhibitor in the treatment of colorectal cancer liver metastasis. The study includes 20 patients with colorectal cancer liver metastasis that has failed first-line therapy and is unresectable. All patients will receive multi-mode ablation to achieve complete remission of liver lesions followed by systemic therapy including PD-1 inhibitor.

This study will provide preliminary data on the efficacy and safety of multi-mode ablation combined with systemic therapy including PD-1 inhibitor in the treatment of colorectal cancer liver metastasis, which could lead to larger randomized trials.

Inclusion Criteria:

1. Age 18-75 years, gender not specified;
2. Pathologically or clinically confirmed colorectal cancer liver metastases, with liver lesions unsuitable for surgical resection or intolerance or refusal of surgical resection;
3. In the case of an unresectable primary tumor or recurrence, the absence of serious complications such as bleeding or obstruction;
4. Failure of first-line treatment, with disease progression or new liver metastases;
5. No more than 5 liver lesions, with single lesion diameter ≤ 3cm;
6. For those who have received previous chemotherapy, radiotherapy or local liver treatment, the interval from the last systemic treatment or local liver treatment should be at least 1 month;
7. Child-Pugh A or B; bilirubin ≤ 3.0 mg/dL, creatinine ≤ 2.5 mg/dL, white blood cell count ≥ 2.0 ×10^9/L, platelets ≥ 100 ×10^9/L;
8. ECOG PS ≤ 2;
9. Willing to accept subsequent treatment regimens that include anti-PD-1 monoclonal antibody therapy.

Exclusion Criteria:

1. Liver function Child-Pugh class C;
2. Expected survival < 3 months;
3. Major organ insufficiency or failure;
4. Active infection;
5. Irreversible coagulation disorders;
6. Refractory massive ascites, pleural effusion or cachexia;
7. Unable to cooperate with treatment;
8. Any other factors deemed inappropriate for inclusion or that may affect the subject's participation in the study, as determined by the investigator.