Patients with metastatic or locally advanced gastrointestinal stromal tumors (GIST) who develop resistance against the two hitherto approved drugs for this disease, the tyrosin kinase inhibitors (TKIs) imatinib and sunitinib, have a poor prognosis. Sometimes a further response may be achieved by other drugs, mainly other TKIs, which have been explored in different studies but not yet have been approved for clinical use. Pazopanib is a TKI inhibiting the tyrosin kinases KIT, PDGFRA, and VEGF 1-3, all of which have important roles in the pathogenesis of GIST. Theoretically, it may function in GIST, and it deserves investigational trials. The drug is approved for metastatic renal cancer and is relatively well tolerated. In this trial (SSG XXI), the disease control rate (DCR) = (CR+PR+SD) after 12 weeks of treatment will be assessed as the primary endpoint, and at the same time trough levels will be measured. Secondary endpoints include ORR, PFS, toxicity, and disease control rate in relation to trough level week 12 and in relation to the primary mutation of the tumor (if known). The goal is to include 72 patients in the trial, which is open and single arm.

Eligibility Criteria:

• Metastatic and/or locally advanced GIST, with diagnosis based on histology with positive c-kit and/or DOG-1, or with a GIST-typical mutation in KIT or PDGFR
• Measurable disease on CT (computed tomography) as defined by RECIST criteria; at least one measurable lesion not given radiotherapy
• History of progressive disease on CT according to RECIST criteria after both imatinib and sunitinib treatment, and also after nilotinib if this drug has been given
• No other TKIs given than imatinib, sunitinib and nilotinib
• Age at least 18 years at the time of diagnosis of GIST
• WHO performance status 0-2
• Resolution of all toxic side effects from earlier TKI treatment and any other potential non-TKI treatment to grade 1 or below
• Sufficient organ functions as defined in the protocol
• Absence of earlier or present certain other conditions as defined in the protocol
• No pregnancy or lactation
• Women with childbearing potential must accept the use of adequate contraception throughout the study period
• Written informed consent