The aim of this study is to evaluate the efficacy and safety of short course radiotherapy followed by fruquintinib combined with Sintilimab as the first-line treatment of advanced mCRC compared to bevacizumab combined with capecitabine in patients unfit for intensive therapy.

Anti-angiogenic therapy combined with immune checkpoint inhibitors in advanced mCRC has shown promising efficacy with acceptable toxicities. Radiotherapy may reshape the tumor immune microenvironment, thereby improving the efficacy of subsequent anti angiogenic drugs combined with immunotherapy.

The study is a prospective, multi-centered, two-stage clinical study with 220 unresectable advanced mCRC patients unfit for oxaliplatin or irinotecan-based intensive chemotherapy enrolled. In phase 1b, 20 patients will be recruited and the efficacy and safety of SCRT followed by fruquintinib plus sintilimab will be explored. In phase 2, 200 patients will be randomized and the efficacy and safety will be compared between SCRT followed by fruquintinib plus sintilimab and capecitabine plus bevacizumab.

Inclusion Criteria:

• Have signed an informed consent;
• 18 to 85 years old (including 18 and 85 years old);
• Histopathologically confirmed unresectable advanced metastatic colorectal adenocarcinoma;
• Have not received anti-tumor treatment for metastatic disease;
• Inability to tolerate intensive treatment regimens based on oxaliplatin or irinotecan as determined by researchers;
• At least one measurable lesion;
• Expected life expectancy ≥ 12 weeks;
• The function of important organs within the 14 days prior to enrollment meets the following requirements (no blood components or cell growth factors are allowed to be used within the 14 days prior to enrollment):
• Neutrophil absolute count ≥ 1.5 × 10^9/L;
• Platelets ≥ 80 × 10^9/L;
• Hemoglobin ≥ 8g/dL;
• Total bilirubin<1.5 times ULN;
• ALT and AST<2.5 times ULN (liver metastasis patients<5 times ULN);
• Serum creatinine ≤ 1.5 times ULN;
• Endogenous creatinine clearance rate>50ml/min;
• International standardized ratio (INR) of coagulation function ≤ 1.5 × ULN, prothrombin time (PT) and activated partial thromboplastin time (APTT) ≤ 1.5 × ULN
• Women of childbearing age or men whose partners have a desire to conceive should take effective contraceptive measures.

Exclusion Criteria:

• Currently has a disease or condition that affects drug absorption, or the patient is unable to take oral drugs;
• Currently has digestive tract diseases such as active gastric and duodenal ulcers, ulcerative colitis, or active bleeding from unresectable tumors, or other conditions determined by the researcher that may cause gastrointestinal bleeding or perforation;
• History of serious cardiovascular and cerebrovascular diseases;
• Other malignant tumors within the past 5 years, excluding skin basal cell or squamous cell carcinoma after radical surgery, or cervical carcinoma in situ;
• Clinically uncontrolled active infection, such as acute pneumonia, active hepatitis B or hepatitis C (hepatitis B virus DNA ≥ 1 × 104 copies/mL or>2000 IU/ml);
• Currently has central nervous system (CNS) metastasis or has a history of unstable or clinically symptomatic brain metastasis;
• Pregnant (positive pregnancy test before medication) or breastfeeding women;
• Urine protein ≥ 2+, or 24-hour urine protein >1.0g;
• Histologically confirmed MSI-H/dMMR tumors;
• Patients deemed unsuitable by the researchers for inclusion in this study.