The epidermal growth factor receptor (EGFR) provides survival signals and is overexpressed in the majority of colorectal cancer. Cetuximab is a recombinant human/mouse monoclonal antibody(MoAb) against EGFR, clinically active in the treatment of human colorectal cancer. Unlike the predictable correlation of response to trastuzumab, another MoAb clinically active in a subgroup of breast cancer patients expressing HER-2/neu, responses to cetuximab in EGFR-expressing colorectal cancer is not predictable.