Study of Pazopanib in the Treatment of Osteosarcoma Metastatic to the Lung

Inclusion Criteria: * Written informed consent or assent * Age \> or = to 16 years * Histologically confirmed diagnosis of osteosarcoma with lung metastasis, who have progressed on the prior line of therapy, or relapsed * Ineligible for curative pulmonary metastasectomy * Eastern Cooperative Oncology Group (ECOG) performance status of 0-2 * Measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 guidelines. At least one measurable lesion must be in the lungs. * Eligible subjects are required to have \> or = to 1 line of multi-agent chemotherapy either neoadjuvantly or adjuvantly. Subjects may have had 0-2 lines of therapy for metastatic disease. * Measured cardiac ejection fraction \> or = to 50% or the institutional lower limit of normal by echocardiogram or MUGA scan. * Adequate organ system function. * Females must be either non-child bearing potential or have a negative pregnancy test within 3 to 5 days prior to the first dose of study drug. Exclusion Criteria: * Children not in the care or custody of a biological parent, adoptive parent, appointed legal guardian, or legally appointed foster care. * Prior exposure to VEGFR tyrosine kinase inhibitor (small molecule or antibody) or VEGFR antibody. * Prior malignancy. Note: Subjects who have had another malignancy and have been disease-free for 3 years, or subjects with a history of completely resected non-melanomatous skin carcinoma or successfully treated in situ carcinoma are eligible. * History or clinical evidence of central nervous system (CNS) metastases or leptomeningeal carcinomatosis, unless previously treated, asymptomatic, and off steroids and anti-seizure medication for 6 months prior to first dose of study drug * Clinically significant gastrointestinal abnormalities that may increase the risk for gastrointestinal bleeding. * Clinically significant gastrointestinal abnormalities that may affect absorption of investigational product. * Presence of uncontrolled infection. * Corrected QT interval (QTc) \> 480 msecs using Bazett's formula. * History of certain cardiovascular conditions within the past 6 months. * Class II-IV congestive heart failure, as defined by the New York Heart Association * Poorly controlled hypertension \[defined as systolic blood pressure (SBP) of ≥ 140 mmHg or diastolic blood pressure (DBP) of ≥ 90mmHg\]. * History of cerebrovascular accident including transient ischemic attack (TIA), pulmonary embolism or untreated deep venous thrombosis (DVT) within the past 6 months. * Prior major surgery or trauma within 28 days prior to the protocol-mandated 4-week drug holiday and/or presence of any non-healing wound, fracture, or ulcer. * Evidence of active bleeding or bleeding diathesis. * Known endobronchial lesions and/or lesions infiltrating major pulmonary vessels that increase the risk of pulmonary hemorrhage. * Hemoptysis of red blood in excess of 2.5 mL (or one half teaspoon) within 8 weeks of first dose of study drug. * Any serious and/or unstable pre-existing medical, psychiatric, or other condition that could interfere with subject's safety, provision of informed consent/assent, or compliance to study procedures. * Unable or unwilling to discontinue use of prohibited medications for at least 14 days or five half-lives of a drug, whichever is longer, prior to the first dose of study drug and for the duration of the study treatment. * Radiation therapy, minor surgery, tumor embolization, chemotherapy, immunotherapy, biologic therapy, investigational therapy or hormonal therapy within 14 days prior to the protocol-mandated 4-week drug holiday. * Administration of any non-oncologic investigational drug within 30 days or five half-lives (whichever is longer) prior to the protocol-mandated 4-week drug holiday. * Any ongoing toxicity from prior anti-cancer therapy that is \> Grade 1 and/or that is progressing in severity, except alopecia. * Known immediate or delayed hypersensitivity reaction or idiosyncrasy to drugs chemically related to pazopanib or excipients that contraindicates participation. * An untreated tumor growth rate of \< 6.1% during the Screening period may exclude some patients.