Monoclonal Antibody Plus Chemotherapy in Treating Patients With Advanced Colorectal Cancer That Overexpresses HER2

Phase II trial to study the effectiveness of the monoclonal antibody trastuzumab and chemotherapy with irinotecan in treating patients who have stage IV colorectal cancer that overexpresses HER2. Monoclonal antibodies can locate tumor cells and either kill them or deliver tumor-killing substances to them without harming normal cells. Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Combining monoclonal antibody therapy with chemotherapy may kill more tumor cells.