The objective of this study is to identify, in clinical samples, the molecular signature of clinically resistant colorectal cancer (CRC) patients for the most current and commonly used therapeutic agents. The goals of this study are two-fold. First, to build a biobank of blood and tissue specimens, prior to starting chemotherapy and at a determined time-point (progression of disease), from patients undergoing the same standard and well established first-line treatments (FOLFOX/bevacizumab or FOLFIRI/bevacizumab) for metastatic colorectal cancer. Second, to use state-of-the-art approaches by various collaborating laboratories to correlate clinical outcomes with molecular events that can be used to predict and circumscribe chemoresistance.