 The purpose of this study is to assess whether treatment with the study drug, panitumumab given concomitantly with every 2 Q2 week oxaliplatin-based chemotherapy and bevacizumab improves progression-free survival PFS compared to treatment Q2-week with oxaliplatin-based chemotherapy and bevacizumab alone. All subjects will receive Q2-week oxaliplatin- or irinotecan-based chemotherapy and bevacizumab. Control arm subjects will not receive concomitant panitumumab therapy. 