Major surgery within 4 weeks before randomization

Last dose of prior chemotherapy received less than 4 weeks prior to randomization

Radiation therapy within the last 4 weeks prior to randomization(with exception of palliative radiotherapy)

Brain metastases or spinal cord compression, unless treated at least 4 weeks before first dose and stable without steroid treatment for 10 days

Significant cardiac events

Previous ZD6474 treatment

An Efficacy Study Comparing ZD6474 to Placebo in Medullary Thyroid Cancer