The purpose of this study is to evaluate the efficacy and safety of QL1706 Injection in combination with bevacizumab and XELOX compared with placebo in combination with bevacizumab and XELOX for first-line treatment in patients with unresectable mCRC.

Inclusion Criteria:

• Patients who voluntarily sign the informed consent form (ICF) and can understand and comply with the study requirements;
• Males and females aged 18 to 75 years old (including boundary value) on the date of signing ICF;
• Unresectable metastatic colorectal adenocarcinoma confirmed by histopathology examination;
• No previous systemic anti-tumor drug therapy for metastatic colorectal adenocarcinoma;
• At least one target lesion as judged by the investigator per RECIST v1.1 (lesions previously treated with topical treatment such as radiotherapy should not be considered as target lesions, unless it is confirmed that there has been definite progression of lesions located in the previous radiotherapy region);
• Be able to provide sufficient previously archived tumor tissue samples or agree to collect tumor tissue samples (≥ 5 unstained pathological tissue sections) by biopsy for biomarker testing. If sufficient tissue samples cannot be provided, it should be determined with the sponsor;
• ECOG PS score of 0 or 1 within 7 days before the first dose;
• Adequate liver, bone marrow, and renal organ function.

Exclusion Criteria:

• Patients had other active malignant tumors within 5 years prior to the first dose. Patients with localized tumors that have been cured, such as basal cell carcinoma of the skin, squamous cell carcinoma of skin, superficial bladder carcinoma, carcinoma in situ of prostate, cervical carcinoma in situ, and breast carcinoma in situ, can be enrolled.
• Previous treatment with radiotherapy at any site within 4 weeks prior to the first dose.
• Previous treatment with postoperative adjuvant therapy with targeted drugs targeting epidermal growth factor receptor (EGFR), vascular endothelial growth factor (VEGF) or its receptor (VEGFR), including but not limited to Bevacizumab, Cetuximab, Panitumumab, Aflibercept, Regorafenib or Anlotinib;
• Previous treatment with any T cell costimulation or immune checkpoint inhibitors, including but not limited to anti-PD-1, anti-PD-L1, anti-PD-L2, anti-CTLA-4, anti-OX-40 or anti-CD137 monoclonal antibodies;
• Participation in a clinical study and treatment with study drug or device within 4 weeks prior to the first dose, or traditional Chinese medicine treatment < 2 weeks from the first dose;
• Patients who have a history of severe (≥ Grade 3) gastrointestinal ulcers, gastrointestinal perforation, fistula formation, intra-abdominal inflammation/abscess, intra-abdominal pneumatosis not due to puncture or surgery, macroscopic digestive tract hemorrhage/melena (excluding hemorrhoidal hemorrhage), and hemoptysis (about 3 mL or more) within 6 months prior to the first dose;
• Uncontrollable pleural effusion, pericardial effusion or ascites requiring drainage;
• Presence of dysphagia and unable to swallow the investigational product;