A Dose-finding Phase Ib Multicenter Study of Imatinib in Combination With the Oral Phosphatidyl-inositol 3-kinase (PI3K) Inhibitor BYL719 in Patients With Gastrointestinal Stromal Tumor (GIST) Who Failed Prior Therapy With Imatinib and Sunitinib

Inclusion Criteria:

- Male or female patients ≥ 18 years of age -WHO performance status (PS) of 0-2
-Histologically confirmed diagnosis of GIST that is unresectable or metastatic
-.Available tissue specimen: • Dose-escalation part: patients must have available
archival tumor tissue which can be shipped during the course of the study. In the
absence of archival tumor tissue, patients must agree to a fresh pre-treatment biopsy
at screening. • Dose-expansion part: patients must have available archival tumor
tissue which can be shipped during the course of the study and must agree to a fresh
pre-treatment biopsy

- Failed prior therapy with imatinib followed by sunitinib for the treatment of
unresectable or metastatic GIST. Note the following specific criteria for the two
parts of the trial: • Dose-escalation part: patients who failed prior therapy with
imatinib and then have failed therapy with sunitinib. Treatment failure may be due to
either disease progression on therapy (both imatinib and sunitinib) or intolerance to
therapy (sunitinib) • Dose-escalation part patients may have had additional lines of
therapy than imatinib and sunitinib dose-expansion part: patients must have
documented disease progression on both imatinib and sunitinib. In addition, patients
may have had no more than two lines of prior therapy (i.e. treatment with imatinib
followed by treatment with sunitinib). • Note: Adjuvant imatinib will not count as a
prior course of imatinib for the purposes of this criterion 6. Radiological (CT/MRI)
confirmation of disease progression (RECIST criteria) during prior therapy with
imatinib and sunitinib will be required for patients entering the Dose-expansion part

Exclusion Criteria:

-Previous treatment with PI3K inhibitors -Patient has active uncontrolled or symptomatic
central nervous system (CNS) metastases Note: A patient with controlled and asymptomatic
CNS metastases may participate in this trial. As such, the patient must have completed any
prior treatment for CNS metastases > 28 days (including radiotherapy and/or surgery) prior
to start of treatment in this study and should not be receiving chronic corticosteroid
therapy for the CNS metastases -Severe and/or uncontrolled concurrent medical condition
that, in the opinion of the investigator, could cause unacceptable safety risks or
compromise compliance with the protocol (e.g. acute or chronic liver, pancreatic disease,
severe renal disease considered unrelated to study disease, chronic pulmonary disease
including dyspnea at rest from any cause) -Patients with diabetes mellitus requiring
insulin treatment and/or with clinical signs or with FPG >120mg/dL / 6.7mmol/L, or history
of documented steroid-induced diabetes mellitus -Patient who has not recovered to grade 1
or better from any adverse events related to previous imatinib and/or sunitinib therapy
before screening procedures are initiated