A Phase 3, Randomized, Double-Blind, Placebo-Controlled, Multi-Center Study Evaluating the Efficacy and Safety of IPI-504 in Patients with Metastatic and/or Unresectable Gastrointestinal Stromal Tumors Following Failure of at Least Imatinib and Sunitinib

o At least 18 years of age at the time of study randomisation
o Histologically confirmed metastatic and/or unresectable GIST.
o Measurable disease on CT or MRI as defined by RECIST
o Documented radiographic progression or intolerance to imatinib and sunitinib.
o Clinical failure of the most recent prior therapy for GIST. Note: There is no limit to the number of prior therapies a patient may have received
o ECOG performance status: 0 or 1.
o Hemoglobin >= 8.0 g/dL
o Absolute Neutrophil Count >= 1.5 x 109/L
o Platelets >= 100 x 109/L
o ALT and AST <= 2.5 x upper limit of normal (ULN), or <= 3.0 x ULN if considered secondary to liver metastases
o Alkaline phosphatase <= 2.5 x ULN, or <= 3.0 x ULN if considered secondary to liver metastases
o Serum bilirubin <= 1.5 x ULN
o PT and PTT <= 1.5 x ULN unless the patient is receiving warfarin. If the patient is receiving warfarin, the INR must be within therapeutic range
o Serum creatinine <= 1.5 x ULN
o Albumin >= 3.0g/dL;Please see the protocol for a detailed definition of all inclusion criteria.

o Previous administration of other known heat shock protein 90 (Hsp90) inhibitors.
o Surgery, radiotherapy, or lesion ablative procedure to the only area of measurable disease.
o Initiation or discontinuation of concurrent medication that is a potent CYP3A inhibitor less than 2 weeks prior to administration of IPI-504 or placebo.
o History of any of the following within the last 6 months: cardiac disease such as acute coronary syndrome or unstable angina, symptomatic congestive heart failure, uncontrolled hypertension, cirrhotic liver disease, cerebrovascular accident, or any other significant co-morbid condition or disease which, in the judgment of the investigator, would place the patient at undue risk or interfere with the study.
o Grade 3 or 4 hemorrhagic event within the last 6 months.
o Known human immunodeficiency virus positivity.
o Sinus bradycardia (resting heart rate < 50 bpm) secondary to intrinsic conduction system disease.
o QTcF >= 470 milliseconds (msec), or previous history of clinically significant QTc prolongation while taking other medications.
o History of prior malignancies within the past 3 years other than non-melanomatous skin cancers that have been controlled, prostate cancer that has been treated and has not recurred, non-muscle-invasive bladder cancer, and carcinoma in situ of the cervix.
o Active or recent history (within 3 months) of keratitis or keratoconjunctivitis confirmed by ophthalmology or optometry exam.
o Presence of Left Bundle Branch Block, Right Bundle Branch Block plus left anterior hemiblock, bifascicular block, or 3rd degree heart block.This does not include patients with a history of these events with adequate control by pacemaker.
o Patients with known central nervous system (CNS) metastases.
o Women who are pregnant or lactating.;Please see the protocol for a detailed description of all exclusion criteria.