 Screening blood tests will be performed to determine eligibility, as well as baseline heart and lung function tests and appropriate scans to measure tumour size and assess radiation within the body. Patients will be given a trace labelled small radiation dose infusion of 131I-hu A33 into a vein followed a week later by the treatment infusion of 131I-hu A33. The first infusion will be given as an outpatient but for the second patients will be hospitalised and confined to a radiation shielded room until radiation levels fall to safe limits. Oral iodine drops will also be given for 28 days in order to protect the thyroid gland from the effects of radioactive iodine. Capecitabine chemotherapy will be taken orally and will commence at the time of the treatment infusion. Each cycle of capecitabine chemotherapy involves the medication being taken twice per day for a total of 14 days followed by 7 days rest. A total of 4 cycles of capecitabine will be given after the treatment infusion. 