Efficacy and Safety of SBRT Followed by Tislelizumab Plus Cetuximab and Irinotecan in Patients With Previously Treated RAS Wild-type Advanced Refractory Colorectal Cancer

Inclusion Criteria: * Aged 18-75 years * Physical Condition Score (ECOG PS) of the Eastern Cancer Cooperative Group (USA) 0 or 1; * Colorectal cancer diagnosed histologically and/or cytologically has metastases or relapses that are not curable by surgery * Have received first - and second-line systemic antitumor therapy for mCRC (chemotherapy drugs may include fluorouracil, oxaliplatin, irinotecan, e.g. XELOX, FOLFOX, FOLFIRI, FOLFOXIRI, XELIRI; Can be combined with or without targeted drugs, such as cetuximab, bevacizumab);And disease progression after second-line treatment; * Evaluation of lung or liver metastases can be evaluated, with stereotactic radiotherapy maneuverability; * At least one measurable lesion as defined in RECIST version 1.1; * Fertile patients must be willing to take effective pregnancy avoidance measures during the study period and ≥120 days after the last dose; Female patients with negative urine or serum pregnancy test results within 7 days or less before the first administration of the study drug; * Have fully understood this study and voluntarily signed informed consent. * Adequate organ and bone marrow function, meeting the following definitions: 1. Blood routine (no blood transfusion, no granulocyte colony stimulating factor \[G-CSF\], no other drug correction within 14 days before treatment);Absolute count of neutrophils (ANC) ≥1.5×109/L;Hemoglobin (HB) ≥9.0 g/dL;Platelet count (PLT) ≥80×109/L; 2. Blood biochemistry, serum creatinine (Cr) ≤ 1.5× upper limit of normal (ULN) or creatinine clearance ≥60 mL/min;Serum albumin ≥2.8g/dL, for patients with poor nutritional status before neoadjuvant therapy, patients who met the requirements through parenteral nutrition could also be included in the group;Total bilirubin (TBIL) ≤ 1.5×ULN;Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) level ≤2.5×ULN; Exclusion Criteria: * 1\. Pregnant or lactating women; * Patients with a known history of allergy to any investigative drug, similar drug or excipient; * Patients with risk of massive gastrointestinal bleeding or gastrointestinal obstruction; * Patients with a history of thromboembolism, except thrombosis caused by PICC; * There are patients with active infection; * Patients with unmanageable hypertension (systolic blood pressure ≥160 mmHg and diastolic blood pressure ≥90mmHg); * Patients with brain metastases with clinical symptoms or imaging evidence; * Contraindications exist in treatment with other chronic diseases; * Patients with a history of immunotherapy-related myocarditis, pneumonia, colitis, hepatitis, nephritis, etc., with current AE ≥ grade 2; * According to the evaluation criteria of NCI CTCAE version 5.0, there are patients with all kinds of toxicities ≥ grade 2 due to previous treatment; * Other conditions that the researchers determined were not suitable for inclusion in the study. * Received any antitumor therapy and participated in other clinical studies within 4 weeks before enrollment.