- Each cycle of treatment is 8 weeks long. All participants will start taking ZD6474 orally, on day one and continue taking it at home thereafter. Cetuximab and irinotecan are given intravenously. Cetuximab is given once a week. Irinotecan will be given to participants that enter the trial once the safe dose of ZD6474 and cetuximab is determined. Irinotecan is given on Day 15 of cycle one, then every other week.