Assuming that the objective response rate (ORR) of neoadjuvant chemotherapy in patients with colorectal cancer peritoneal metastasis is approximately 0.40 , a total sample size of 30 patients is required.

Step 1:

Ten patients will be initially enrolled. If the number of responders (CR/PR) is < 2, the study will be terminated early for futility.

If the number of responders is > 8, the treatment regimen will be considered effective, and the study may be concluded early.

Step 2:

If the number of responders in Step 1 is between 2 and 8, the study will continue to enroll an additional 20 patients until completion.

Treatment regimen: CapeOX + Pirfenidone + Sintilimab

CapeOX:

Oxaliplatin (L-OHP) 130 mg/m², IV infusion over 2 hours on Day 1 Capecitabine 1,000 mg/m² orally, twice daily for 14 consecutive days Repeated every 3 weeks

Pirfenidone:

Oral administration, 200 mg three times daily, taken on an empty stomach (low-dose regimen)

Sintilimab:

200 mg per dose, IV infusion once every 3 weeks The first 4 cycles are provided free of charge. After the fourth cycle, tumor response will be assessed; if continued use is required, a "buy 2, get 2 free" policy will apply.

Tumor response evaluation will be performed after 4 treatment cycles.

Inclusion Criteria:

1. Age between 18 and 75 years;

2. Radiologically (CT/MRI/PET-CT/FAPI-PET) or pathologically confirmed peritoneal metastasis from colorectal cancer;

3. Planned to receive first-line chemotherapy;

4. ECOG performance status of 0-1;

5. Adequate hematologic, hepatic, and renal function:

   1. Neutrophil count ≥ 1.5 × 10⁹/L
   2. Platelet count ≥ 100 × 10⁹/L
   3. Hemoglobin ≥ 8.0 g/dL
   4. Creatinine clearance > 30 mL/min
   5. For patients without liver metastasis: AST and ALT ≤ 2.5 × upper limit of normal (ULN)
   6. Total bilirubin ≤ 2 × ULN
   7. APTT and PT ≤ 1.5 × ULN

Exclusion Criteria:

1. Individuals with a tendency to bleed, hereditary bleeding disorders, or evidence of coagulation abnormalities;
2. Pregnant or breastfeeding women, or women of childbearing potential who are not using effective contraception;
3. Expected survival ≤ 3 months;
4. Participation in another investigational drug trial within the past 4 weeks;
5. Prior treatment with any anti-PD-1, anti-PD-L1, anti-PD-L2, or anti-CTLA-4 antibodies (or any other antibodies targeting T-cell co-stimulation or immune checkpoint pathways);
6. Uncontrolled neurological or psychiatric disorders that may affect compliance or the ability to report treatment responses;
7. Known allergy to any study drug.