It is common for colorectal cancer cells to contain growth receptors, like antennae, on their surface which regulate their growth. The drugs used in this trial have been shown to be effective in targeting one of these growth receptors; the epidermal growth factor receptor (EGFR). Cetuximab is an antibody (protein produced by the immune system involved in the defense of the body against infections) against EGFR. Cetuximab has been shown to improve the survival of patients with chemotherapy refractory advanced colorectal cancer. Erlotinib is a protein that prevents activation and hence signaling by EGFR. Erlotinib improves survival in patients with advanced lung cancer. Although, each of these drugs are known to be effective at inhibiting EGFR when they are given alone, at least in some cases, it is hoped that using two drugs that target the same receptor pathway in different ways will provide a more effective treatment.