Pazopanib in Patients With Recurrent or Metastatic Head and Neck Squamous Cell Carcinoma

Inclusion Criteria: 1. Histologically confirmed HNSCC. 2. Recurrent or metastatic setting, refractory to previous cisplatin or carboplatin-based chemotherapy. 3. At least one measurable lesion (according to RECIST v 1.1 criteria). 4. Eastern Cooperative Oncology Group performance status 0 to 2. 5. Age\>18y/o,\<=70y/o. 6. Adequate bone marrow, hepatic, and renal functions as evidenced by the following: * Absolute neutrophil count\>=1,500 cells/L, platelet count\>=100,000 cells/L, and hemoglobin\>=9 g/dL. * Total bilirubin\<=1.5 X ULN, AST/ALT\<=3.0 X ULN * Creatinine\<=1.5 mg/dL. 7. Informed consent, obtained in writing. Exclusion Criteria: 1. Second malignancy. 2. Locoregional recurrence amenable to definite surgery or radiation again. 3. Brain/meningeal metastasis with IICP or bone metastasis with spinal cord compression. 4. Pregnancy or nursing women. 5. Having received more than two prior lines of intravenous chemotherapy in the palliative setting. 6. Having received antiangiogenesis agent in the palliative setting. 7. Having received chemotherapy or radiation therapy or surgery within 3 weeks. 8. Major systemic diseases those are inappropriate for systemic chemotherapy according to clinician's professional judgment. 9. Mental status not fit for clinical trials. 10. Clinically significant gastrointestinal abnormalities that may increase the risk for gastrointestinal bleeding including, but not limited to: * Active peptic ulcer disease * Known intraluminal metastatic lesion/s with risk of bleeding * Inflammatory bowel disease (e.g. ulcerative colitis, Crohn's disease), or other gastrointestinal conditions with increased risk of perforation * History of abdominal fistula, gastrointestinal perforation, or intra abdominal abscess within 28 days prior to beginning study treatment. 11. Corrected QT interval (QTc)\>480 msecs using Bazett's formula. 12. Poorly controlled hypertension defined as SBP\>=140 mmHg or DBP\>=90mmHg 13. Concomitant diseases that might be aggravated by investigational drugs: * Active or non-controlled infection. * Severe upper gastrointestinal bleeding. * History of any one or more of the following cardiovascular conditions within the past 12 months: * Cardiac angioplasty or stenting, * Myocardial infarction, * Unstable angina, * Symptomatic peripheral vascular disease, * Class III or IV congestive heart failure, as defined by the New York Heart Association (NYHA) 14. Hemoptysis within 6 weeks of first dose of Pazopanib, prior major surgery within 4 weeks of first dose of Pazopanib, or presence of any non-healing wound/fracture.