This is a 2 arms study concerning patients under imatinib treatment for at least 10 years of treatment with locally advanced/metastatic GIST.
In the first arm, patients will discontinue Imatinib treatment. This arm will allow to determine if the re-introduction of Imatinib at relapse is still an efficient treatment for the control of disease.
In the second arm, patients will continue Imatinib treatment, allowing to determine if the continuation of this treatment is efficient for disease control, by the rate of non-progression disease.
Patients ≥18 years of age;
Histologically documented diagnosis of malignant advanced/metastatic GIST with immunohistochemical documentation of c-kit (CD117) expression either by the primary tumor or metastases;
Eastern Cooperative Oncology Group (ECOG) - Performance status (PS) 0 to 2 evaluated within 7 days prior to the date of inclusion.
Patient must be under imatinib treatment (at 300 or 400mg/day) maintained for 10 years or over with no more than 12 months in total or 3 consecutive months of interruption during the treatment period;
Patient concurrently using other approved or investigational antineoplastic agents;
Patient with GIST harboring the mutation D842V in PDGFRA;
Major concurrent disease affecting cardiovascular system, liver, kidneys, haematopoietic system or else considered as clinically important by the investigator and that could be incompatible with patient's participation in this trial or would likely interfere with study procedures or results;
Prior history of other malignancies other than study disease (except for basal cell or squamous cell carcinoma of the skin or carcinoma in situ of the cervix) unless the patient has been free of the disease for at least 3 years;