SBRT Combined With CAPEOX, Bevacizumab, and PD-1 Inhibitor for the Treatment of RAS-Mutant, MSS-Type, Unresectable Metastatic Colorectal Cancer.

Prior treatment

• Complex situations with concurrent active bleeding, perforation, or requiring emergency surgery.
• Have received systemic anti-cancer treatment for rectal cancer.
• Any grade 2 or above toxic reactions (classified according to the Common Terminology Criteria for Adverse Events (CTCAE) 5th edition) caused by previous treatment that have not subsided (excluding anemia, hair loss, and skin pigmentation).

Other illness

• Patients with any active autoimmune diseases or a history of requiring steroid or immunotherapy treatment.
• Simultaneously present with other non colorectal cancer tumor diseases.
• Patients with interstitial lung disease, non infectious pneumonia or uncontrollable systemic diseases (such as diabetes, hypertension, pulmonary fibrosis and acute pneumonia).
• Patients who are known or have been tested for human immunodeficiency virus (HIV) or acquired immunodeficiency syndrome (AIDS).
• Known or suspected history of allergies to any relevant drugs used in the trial

Lab values

• Patients who have received antibodies against programmed death receptor-1 (PD-1) or its ligand (PD-L1), as well as antibodies against cytotoxic T lymphocyte associated antigen 4 (CTLA-4).

Other

• Pregnant or lactating women.

• Aged 18-75 years, regardless of gender.
• Lower edge of the lesion located ≥12 cm from the anal verge.
• Histologically confirmed colorectal adenocarcinoma.
• Confirmed as unresectable by multidisciplinary team (MDT) evaluation.
• RAS mutation-positive.
• Microsatellite/mismatch repair status: MSS/pMMR.
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
• Expected survival ≥3 months.
• Adequate hematological, hepatic, and renal function:
  • Neutrophil count ≥1.5 × 10⁹/L; Platelet count ≥75 × 10⁹/L; Serum total bilirubin ≤1.5 × upper normal limit (UNL); Aspartate aminotransferase (AST) ≤2.5 × UNL; Alanine aminotransferase (ALT) ≤2.5 × UNL; Serum creatinine ≤1.5 × UNL.
• Karnofsky Performance Status (KPS) score ≥70.
• Adequate organ function with no contraindications to surgery, radiotherapy, chemotherapy, or immunotherapy.
• No prior chemotherapy or other antitumor therapy before enrollment.
• No prior immunotherapy received.
• Willingness and ability to comply with the study protocol during the trial period.
• Signed written informed consent.