Inclusion Criteria:

• Patient ≥18 years
• Tumor biopsy with histopathologic confirmation of rectal adenocarcinoma as primary histology
• Patient with measurable disease at the baseline visit
• Tumor that meets all the following criteria in high-resolution MRI (3-mm slices) of the pelvis:
• Distal border of tumor more than 5cm from the external edge of the anus and below the sacral promontory (located in the anatomic rectum). One or two of the following: T3>5mm; Presence of extramural venous invasion; Tumor ≥2 mm from the mesorectal fascia
• Candidate for complete surgical resection (R0) with sphincter preservation surgery, prior to the administration of any therapy
• Candidate for systemic therapy with XELOX/BVZ
• ECOG: 0-2
• ANC≥1.5 cells/mm3, Hb>8.0 g/dL, platelets>150,000/mm3 in 2 previous weeks
• Patient who signed the informed consent

Exclusion Criteria:

• Stage T4.
• Distant metastases
• Tumor with an intraperitoneal distal border
• Tumor presenting initially in a low location and judged, prior to any treatment, to require abdominoperineal resection
• Previous chemotherapy for colorectal cancer or incomplete recovery from oncologic surgery or other previous major surgery that, in the opinion of the investigator, precludes the use of a combined modality therapy
• Serum creatinine <1.5 ULN
• Patient who has received previous pelvic radiotherapy
• Patient with an uncontrolled infection
• Presence of a high degree of obstruction (intestinal lumen ≤ 1 cm), unless the patient has undergone protective surgical bypass or an endoscopic stent procedure
• Pt with a history of an arterial thromboembolic event during the previous year.This includes angina (stable or unstable),myocardial infarction (MI),cerebrovascular accident (CVA),or other relevant history in the opinion of the investigator.Note: A patient with a history of thrombotic events, such as deep venous thrombosis, pulmonary embolism, MI or ACV, within the 6 months preceding recruitment may be considered for participation in the clinical trial if they are receiving stable doses of anticoagulant therapy. Similarly, patients being anticoagulated for atrial fibrillation or other conditions can participate if they are receiving a stable dosage of anticoagulant therapy. Clinicians must consider the higher risk of therapy with BVZ among patients with a history of thromboembolic disorders so the decision to allow the patients to participate remains at the discretion of the physician
• Previous treatment with another investigational antitumoral therapy in the 30 days prior to beginning treatment
• History of previous malignancy in the past 5 years, excepting basocellular or squamous cell skin cancer, or properly treated cervix cancer in situ
• Woman with a positive pregnancy test in urine or serum during recruitment, prior to the administration of the study medication, or within 72 hours of beginning to take the study medication, or a woman who is nursing
• WOCBP who does not wish to use or cannot use an effective contraceptive method to avoid pregnancy during the complete study period up to 4 weeks after ending the study.Male subjects also must agree to use an effective method of contraception.Note: WOCBP refers to any woman who has experienced menarche and has not undergone successful surgical sterilization or is not postmenopausal (defined as amenorrhea≥12 consecutive months,or women with hormonal replacement therapy and documented serum levels of follicle stimulating hormone).Even women who are using oral, implanted or injectable contraceptive hormones, mechanical products such as an intrauterine device or barrier methods to prevent pregnancy,or who practice abstinence or have a sterile partner, must be assumed to be WOCBP
• Patient with any other condition or concurrent medical or psychiatric disease who,in opinion of the investigator, is not eligible to enter the study
• Known hypersensitivity to any component of the study drug (XELOX/bevacizumab) or radiotherapy