A Study to Investigate the Safety and Efficacy of AT13387, Alone or in Combination With Imatinib, in Patients With GIST

Inclusion Criteria: * Ability to understand the risks of the study and to provide signed and dated informed consent and authorization to use protected health information (in accordance with national and local subject privacy regulations). * Age 18 years or older. * Unresectable and/or metastatic malignant GIST with objective progression of disease following treatment with a maximum of 3 tyrosine kinase inhibitors (TKIs) including imatinib. To clarify, it is the number of TKIs - up to a maximum of three agents, including imatinib - that is the criterion for entry, not the number of prior courses of TKI treatment. * Measurable disease. * ECOG performance status 0 or 1. * Negative blood or urine pregnancy test (within 7 days prior to commencing treatment), or documented evidence of surgical sterility, or natural or treatment-induced post-menopausal status with last menses \>1 year ago. * Willing to provide a tissue block or unstained slides of archived tumour for central pathology review and genotyping, or a full pathology report and results of genotyping of a previous tumour sample, or willing to undergo a new tumour biopsy for central pathology review and genotyping during the screening period of the study (prior to dosing) Exclusion Criteria: * Pregnancy or lactation (women of childbearing potential must have a negative serum or urine pregnancy test within 7 days prior to commencing treatment ). Male and female patients of childbearing potential must use appropriate birth …