XELOX/mFOLFOX Plus Vitamin D3 vs. XELOX/mFOLFOX as Firstline Chemotherapy in mCRC

Inclusion Criteria: * Signed written informed consent. * males and females, ≥18 years of age * All subjects must have inoperable, advanced or metastatic colorectal cancer and have confirmed histologically adenocarcinoma. * Subject must be previously untreated with systemic treatment given as primary therapy for advanced or metastatic disease. * Prior adjuvant or neoadjuvant chemotherapy and/or radiotherapy are permitted as long as the last administration of the last regimen occurred at least 12 months prior to randomization. * ECOG performance status score of 0 or 1. * Subjects must have at least one measurable lesion or evaluable disease by CT of MRI per RECIST1.1 criteria. * Screening laboratory values must meet the following criteria in 7days before the first day of cycle 1: 1. Hemoglobin ≥9.0g/dL; 2. Neutrophils ≥1500/mm3; 3. Platelet ≥100,000/mm3; 4. Total Bilirubin ≤1.5\*ULN 5. AST ≤2.5\*ULN (or ≤5.0\*ULN if liver metastases are present), and ALT ≤2.5\*ULN (or ≤5.0\*ULN if liver metastases are present) 6. Serum creatinine ≤1.5\*ULN or calculated creatinine clearance \>50mL/min * Women of childbearing potential must have a negative serum or urine pregnancy test within 7 days before randomization. All subjects of childbearing potential must agree to follow instructions for method of contraception for the duration of study treatment and 6 months after the last dose of study treatment. * Life expectancy ≥3 months. Exclusion Criteria: * Concurrent diseases: 1. Prior malignancy active cancer except for locally curable cancer that have been cured over 5years,or carcinoma in situ. 2. Known brain metastasis 3. Any serious or uncontrolled medical disorder or active infection. 4. Known history of positive test for HIV or AIDS; 5. Hepatitis B virus or hepatitis C virus is active; * Within 4 weeks before randomization had operation, enlarged area radiotherapy(local radiotherapy within 2weeks) and other study drugs. * Subjects with ≥ Grade 2 peripheral neuropathy. * Pregnancy or breastfeeding.