The purpose of this study is to compare sensitivity, specificity and accuracy of PET, DW MRI and CT separately and combined for the evaluation of treatment response and progression-free survival in patients with GIST.

Inclusion Criteria:

• Metastatic GIST patients suitable for TKI treatment
• GIST patients pursuing preoperative neoadjuvant TKI treatment

Exclusion Criteria:

• Patients with contraindications to MRI and/or TKI treatment. For patients with renal failure, CT without intravenous contrast will be performed according to clinical practice.
• Patients who do not sign the consent paper for any reason or do not accept the study premises or patients who wish to withdraw for any reason during the study

GIST patients suitable for medical treatment with targeted therapies.