• Changes in FDG-PET imaging [ Time Frame: 28 days ] [ Designated as safety issue: No ]
  

• Characterize the safety profile of BIIB021 [ Time Frame: Duration of study ] [ Designated as safety issue: No ]
  

Inclusion Criteria:

• Ability to understand the purpose and risks of the study and provide signed and dated informed consent and authorization to use protected health information (PHI) in accordance with national and local subject privacy regulations.
• Age greater than or equal to 18 years at the time of informed consent.
• Pathologically confirmed GIST refractory to, intolerant of, or not a candidate for imatinib and sunitinib therapy.
• ECOG performance status of less than or equal to 2.

• Required laboratory values:

  • Absolute neutrophil count (ANC) greater than or equal to 1500 cells/mm3, platelet count greater than or equal to 100,000 cells/mm3, hemoglobin greater than or equal to 9 gm/L.
  • Bilirubin less than or equal to 1.5 x upper limit of normal (ULN), alanine aminotransferase (ALT) or aspartate aminotransferase (AST) less than or equal to 2.5 x ULN; except in subjects with known hepatic metastasis, where AST or ALT can be less than or equal to 5.0 x ULN.
  • Serum creatinine less than or equal to 2.0 x ULN.
  • International Normalized Ratio (INR) less than or equal to 1.5 x ULN.
  • All other values less than or equal to NCI CTCAE Grade 1.
• Female subjects of childbearing potential must have a negative pregnancy test during screening.
• Male and female subjects of childbearing potential must practice effective double barrier contraception during the study and continue contraception for 3 months after their last dose of study drug.

Exclusion Criteria:

• Pregnant or nursing women.
• Prior treatment with imatinib, sunitinib, or sorafenib within 14 days of Day 1.
• Prior treatment with Hsp90 inhibitors at any time.
• Prior antitumor therapies including prior experimental agents, approved antitumor small molecules (excluding imatinib, sunitinib, and sorafenib) and biologics, or radiotherapy within 28 days or <3 half lives (whichever is longer) before start of BIIB021 treatment.
• Diabetes and/or concurrent severe or uncontrolled other medical disease (i.e., systemic infection, hypertension, coronary artery disease, congestive heart failure).
• Active symptomatic fungal, bacterial, and/or viral infection including active HIV or viral (A, B, or C) hepatitis.
• Problems with swallowing or malabsorption.
• Chronic diarrhea (excess of 2 to 3 stools/day above normal frequency).
• Inflammatory gastrointestinal diseases including gastritis, ulcerative colitis, Crohn's disease, or hemorrhagic coloproctitis.
• Major surgery within 28 days of first administration of study treatment.
• Active or untreated brain metastasis.