Study to Identify Mechanisms of Resistance to Standard Therapy in Patients With Metastatic Colorectal Cancer

This is a multicenter translational study to understand therapeutic resistance in patients undergoing first-line chemotherapy (FOLFOX/Avastin, or FOLFIRI/Avastin) for metastatic colorectal cancer. Tissue samples from liver metastasis will be collected and banked before the start of chemotherapy and at the time of progression. Additionally, blood samples will be drawn monthly and stored in the tissue biobank.