A group of colorectal cancer (CRC) patients treated with chemotherapy and Bevacizumab (Bev) maintain the same sensitivity after progression to maintenance treatment because they remain dependent on VEGF angiogenic mediator, while other patients in whom there is an angiogenic switch (AS) become dependent on other angiogenic cytokines and become resistant to Bev chemotherapy combinations .

Inclusion Criteria:

• Diagnosis of stage IV colorectal adenocarcinoma.
• Age ≥ 18 years .
• Measurable disease by RECIST criteria.
• Life expectancy ≥ 6 months.
• Candidate to receive treatment with first-line chemotherapy.
• Availability of tumor tissue.

Exclusion Criteria:

• Patients who have received prior treatment with first-line chemotherapy for metastatic disease.
• Patients in whom there is contraindication to the administration of either drug used in the study: capecitabine, irinotecan, oxaliplatin or Bev.
• Patients receiving anticoagulant oral treatment.
• Patient with diagnosis of other malignancies within 5 years prior to diagnosis except basal cell carcinoma or cervical carcinoma · in situ. · The inclusion of patients with malignant disease diagnosed more than 5 years ago without recurrence in the previous 3 years will be analyzed individually
• Patients with bone disease as the only manifestation of the disease.