The purpose of this study is to evaluate the clinical benefit of the KIT inhibitor XL820 in subjects with advanced gastrointestinal stromal tumors (GIST) who are resistant to or intolerant of Imatinib and/or Sunitinib.

Inclusion Criteria:

• Patients with metastatic or locally advanced or unresectable GIST who have intolerance of or disease progression following prior treatment with imatinib and/or sunitinib
• ECOG (Eastern Cooperative Oncology Group) performance status ≤2
• Must have measurable disease per RECIST (Response Evaluation Criteria in Solid Tumors)
• Recovery from toxicity from prior therapy to Common Terminology Criteria for Adverse Events (CTCAE) v3.0 Grade ≤1 or to subject's baseline status
• Adequate organ and marrow function
• Sexually active subjects (male and female) must agree to use accepted methods of contraception during the course of the study and for 3 months following discontinuation of study drugs.
• Female subjects of childbearing potential must have a negative pregnancy test at enrollment.

Exclusion Criteria:

• Therapy with imatinib or sunitinib within 14 days before the first dose of study drug
• Chemotherapy, immunotherapy, targeted therapy, chemoembolization, or any investigational drug for the treatment of GIST after the last dose of imatinib or sunitinib
• Anticoagulation with warfarin or coumarin-related compounds
• Radiation to ≥25% of bone marrow within 28 days of study entry
• Treatment with other investigational agents within 28 days of the first dose of XL820
• Known central nervous systems metastases
• Uncontrolled or intercurrent illness
• Pregnancy or breast-feeding
• Active bacterial or viral infection requiring systemic treatment