A Comparison of mXELIRI Regimen and FOLFIRI Combined Bevacizumab Regimen as First-line Chemotherapy Regimen for Metastatic Colorectal Cancer

Inclusion Criteria: 1. Signed informed consent; 2. ECOG≤1; 3. Age≥18； 4. Histologically or cytologically confirmed unresectable metastatic colorectal cancer with no previous chemotherapy or molecular targeted therapy; 5. At least one evaluable lesion per RECIST (Response Evaluation Criteria in Solid Tumors) 1.1; 6. life expectancy \>12 weeks; 7. Adequate bone marrow and organ function. Hb≥9 G/L; Absolute neutrophil ≥ 1.5 G/L; PLT ≥100 G/L ;ALT/AST ≤2 ULN or ≤5ULN with liver metastases;ALP ≤2.5 ULN or ≤5ULN with liver metastases or ≤10ULN with bone metastases ; TBIL ≤1.5 ULN; Cr≤1.0 ULN; 8. Urinary protein excretion \< 2+ (dipstick). If \> or equal 2+ proteinuria is detected with dipstick, a 24-hour period urine test will be performed and the result should be \< or equal to 1 g/24 hours to permit the inclusion of the patient in the clinical trial. Exclusion Criteria: 1. Pregnant or lactating women； 2. Sexually active women (of childbearing potential) or men unwilling to adopt an effective method of birth control during the course of the study； 3. Previous treatment with Irinotecan or anti-VEGF antibodies; 4. Any previous malignancy within 5 years prior to study entry, except for cured basal cell carcinoma of skin or carcinoma-in-situ of the uterine cervix; 5. History of acute coronary syndromes (including myocardial infarction and unstable angina) within 6 months prior to study entry, or history or evidence of current ≥ Class II congestive heart failure as defined by New York Heart Association (NYHA); 6. Uncontrolled hypertension and severe arrhythmia requiring drug treatment; 7. Present with non-healing fractures or wounds of skin; 8. History of previous abdominal fistula, gastrointestinal perforation or intra-abdominal abscesses within 6 months before randomization; 9. Major surgery, open surgical biopsy or significant traumatic injury within 4 weeks or needle biopsy within 7 days before randomization before randomization； 10. Evidence or history of bleeding diathesis or coagulopathy； 11. Known or suspected allergy or hypersensitivity to any component of Bevacizumab, xeloda, irinotecan, or 5-FU/LV; 12. Clinical or radiological evidence of CNS metastases; 13. History of unexpected serious adverse events to fluoropyrimidine treatments or known dihidropyrimidine dehydrogenase (DPD) deficiency; 14. Patients subjected to organ allografts who require immunosuppressive treatment; 15. Prior adjuvant or neoadjuvant treatment for metastatic colorectal cancer is allowed, as long as it has concluded at least 6 months before beginning the treatment of the study; 16. If adjuvant treatment has previously been administered, the patients cannot have shown progression of the disease during treatment nor during the 6 months following termination thereof; 17. Prior radiotherapy is allowed if it has not been administered in the target lesions selected for this study, unless progression of said lesions in the irradiated field is documented, and as long as treatment has concluded at least 4 weeks before beginning the study; 18. Prior surgical treatment of the disease in stage IV is allowed; 19. Use of full dose of oral or parenteral anticoagulants ( at least 10 days before the initial study treatment or thrombolytic agents. Low dose of warfarin is allowed, with an INR ≤ 1.5; 20. Subject requiring chronic use of high dose aspirin (\> 325 m/day) or non-steroidal anti-inflammatory treatment ; 21. Received any investigational drug or agent/ procedure, i.e. participation in another treatment trial within 4 weeks of randomisation.