Efficacy/Safety Study of Bevacizumab,Capecitabine,Oxaliplatin to Metastatic Colorectal Adenocarcinoma Elderly Patients.

The efficacy will be determined by objective response rate following RECIST criteria. In several clinical trials with Bevacizumab, there has been demonstrated that elderly patients benefits as well as the younger of a combination therapy with chemotherapy plus Bevacizumab, but these results have come from subgroup analyses of trials not specifically design to test the effect of these combinations on the elderly. This clinical trial is specific only for elderly patients and we expect to confirm the benefits demonstrated in other clinical trials where the elderly patients were a number reduced. This clinical trial includes 3 substudies: \- Assessment of tumor response of CRC liver metastases to treatment with Avastin in combination with Capecitabine and Oxaliplatin as first line treatment by dynamic ultrasound contrast. Main objective: Assess the performance of dynamic contrast ultrasonography (CEUS, Contrast Enhanced UltraSound) with quantification of tumor perfusion in the evaluation of tumor response of liver metastases of colorectal carcinoma to treatment with Avastin in combination with Capecitabine and Oxaliplatin. -Evaluation of the antiangiogenic activity of bevacizumab combined with oxaliplatin and capecitabine in first line treatment using MDCT perfusion studies in liver metastases of colorectal cancer in patients over 70 years. Main objective:Determine whether the observed changes in perfusion CT studies performed at 2 weeks of starting treatment compared to baseline are significant predictors of free time to disease progression in patients in the trial and defined as the time since the start of treatment until objective progressive disease by RECIST criteria. -Characterization of resistance to bevacizumab in colon cancer in elderly patients. Main objective: To evaluate the involvement of serum markers and markers in the primary tumor in the resistance to bevacizumab.