OUTLINE: This is a dose escalation study of azacitidine. Patients undergo a control phase consisting of oral liothyronine sodium twice daily on weeks 1-4 and a low iodine diet on weeks 4-7. At week 6, patients receive a scan dose of iodine I 131 followed by whole body scanning over 5 days. Beginning at week 7, patients undergo a treatment phase consisting of oral liothyronine sodium twice daily for 3 weeks, azacitidine subcutaneously daily for 10 or 20 days (weeks 7-11) and a low iodine diet on weeks 8-11. During week 11, patients undergo additional whole body scanning over 5 days followed by a therapeutic dose of iodine I 131. Patients achieving successful therapy receive 5 additional doses of azacitidine. Cohorts of 4 patients receive escalating doses of azacitidine until demonstrable radioiodine uptake is seen or the maximum tolerated dose (MTD) is determined. The MTD is defined as the dose preceding that at which 2 of 8 patients experience dose limiting toxicity. Patients are followed weekly for 8 weeks.