Inclusion Criteria:

• Signed informed consent.
• Age ≥ 18.
• Patients must have a life expectancy of at least 3 months
• Patients must have a Karnofsky performance status ≥ 70%
• Patients must have histologically confirmed thyroid cancer (TC)
• Tumor disease must be progressive (evidence of disease progression within 6 months before starting the study for follicular and medullary thyroid cancer or symptomatic disease)
• Patients should not be candidates for surgical resection, external beam radiotherapy or radioiodine
• Patients must have measurable disease defined by Response Evaluation Criteria in Solid Tumors (RECIST), such as at least one lesion at least 2 cm in length by conventional computed tomography (CT) techniques or at least 1 cm by spiral CT scan
• Patients must not have more than one previous systemic treatment for cancer
• Resolution of all acute toxic effects of any prior local treatment to National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE version 3.0) grade < 1
• Patients must have discontinued from radiation therapy at least 4 weeks before start of study treatment and must have recovered from any toxic effects of treatment
• Patients must have adequate organ function defined as: Platelets > 100 x 10*9/L, Hemoglobin > 8 g/dl, ANC > 1.5 x 10*9/L, Bilirubin < 3 mg/dL, AST and ALT < 2.5 x the upper limit of normal (ULN) or < 5 x the ULN for liver metastases, INR < 1.7 or prothrombin time < 6 sec over ULN, Serum creatinine < 1.5 x ULN
• Patients with reproductive potential must use medically acceptable contraceptive methods (oral contraception or an intrauterine device [IUD])
• Willingness and ability to comply with all study procedures

Exclusion Criteria:

• Prior treatment on sunitinib or other anti-angiogenic therapy
• NCI CTCAE grade 3 hemorrhage < 4 weeks of starting study treatment
• Diagnosis of any second malignancy < 3 years, except basal cell carcinoma, squamous cell skin cancer, or in situ carcinoma of the cervix uteri that has been adequately treated with no evidence of recurrent disease for 12 months
• History of or known brain metastases, spinal cord compression, or carcinomatous meningitis, or new evidence of brain or leptomeningeal disease
• Any of the following within the 12 months prior to study drug administration: severe/unstable angina, myocardial infarction, coronary artery bypass graft, symptomatic congestive heart failure, cerebrovascular accident, including transient ischemic attack, or pulmonary embolism
• Ongoing cardiac dysrhythmias of NCI CTCAE grade > 2, atrial fibrillation of any grade, or prolongation of the QTc interval to > 450 msec for males or > 470 msec for females
• Hypertension that cannot be controlled by medications
• Treatment with anticoagulant agents and treatment with therapeutic doses of warfarin currently or within 2 weeks prior to first day of sunitinib administration
• Inability to swallow oral medications, or presence of active inflammatory bowel disease, partial or complete bowel obstruction or chronic diarrhea
• Known human immunodeficiency virus (HIV) or acquired immunodeficiency syndrome (AIDS)-related illness
• Pregnancy or breastfeeding
• Other severe acute or chronic medical or psychiatric condition, or laboratory abnormality that may increase the risk associated with study participation or study drug administration, or may interfere with the interpretation of study results, and in the judgment of the investigator would make the patient inappropriate for entry into this study
• Receipt of any investigational agent prior to study entry
• Current treatment on another therapeutic clinical trial