This study is an open-label, multicenter, Phase I dose-escalation study of the combination of AMN107 and imatinib (STI571) in patients with imatinib-resistant GIST. This study is designed to determine the Phase II dose of AMN107 and imatinib when administered together in patients with imatinib-resistant GIST, and to characterize the safety, tolerability and pharmacokinetic (PK) profile of this combination.

Inclusion Criteria:

• Patients with gastrointestinal stromal tumor (GIST).
• Patients who have had disease progression during imatinib therapy with 800 mg.
• Ability to understand and willingness to sign a written informed consent document.

Exclusion Criteria:

• Patients with prior or concomitant malignancies other than GIST with the exception of previous or concomitant basal cell skin cancer or previous cervical carcinoma in situ.
• A history of impaired cardiac function or uncontrolled cardiovascular disease.
• Severe and/or uncontrolled concurrent disease that could cause unacceptable safety risks such as impairment of gastrointestinal (GI) function or GI disease that may significantly alter the absorption of AMN107.
• Currently taking certain medications that could affect an electrocardiogram result.
• Women who are pregnant or breast feeding.
• Patients unwilling or unable to comply with the protocol.

NOTE: Additional inclusion and/ or exclusion criteria may apply.