Neoadjuvant Bevacizumab + Chemotherapy Combined With Short-course Radiotherapy

Inclusion Criteria: 1. A biopsy proven histological diagnosis of rectal adenocarcinoma； 2. An ARMS-PCR proven KRAS, NRAS mutation, excluding BRAF mutation or microsatellite instablility-High; 3. No intestinal obstruction, distant metastasis was excluded by CT, MRI or PET / CT; 4. MRI proven T3c-T4, CRM positive, N2, extramural vascular invasion positive or lateral lymph node positive of locally advanced rectal cancer; 5. Age between 18-75 years; 6. ECOG (Eastern US Cooperative Oncology Group) score: 0-1; 7. Has sufficient organ function: * Hemopoietic function: hemoglobin ≥ 90 g / L, platelet ≥ 80 g / L × 109 / L, * neutrophils ≥ 1.5 × 109/L * Liver function: ALT and AST \< 2.5 × ULN; * Renal function: serum creatinine \< 1.5 ULN; 8. Willing to participate and informed consent signed； Exclusion Criteria: 1. An ARMS-PCR proven RAS wild type, BRAF mutation and microsatellite instablility-High; 2. Patients having undergone chemotherapy, radiotherapy or surgery for colorectal cancer; 3. Patients with other uncontrolled malignant tumors (except early-stage basal cell carcinoma or cervical carcinoma in situ) ; 4. Female patients who are pregnant or breastfeeding; 5. Patients with severe heart, liver, or kidney, or neurological or psychiatric disease; 6. Patients with active infection; 7. Poor overall health status, ECOG ≥ 2; 8. Patients with concomitant diseases that seriously endanger the safety of patients or affect the completion of the study in the judgment of the investigator; 9. Known hypersensitivity reactions to any investigational drugs;