Efficiency of Imatinib Treatment Maintenance or Interruption After 3 Years of Adjuvant Treatment in Patients With Gastrointestinal Stromal Tumours (GIST)

This is a 2 arms study concerning patients with primary GIST who followed an Imatinib adjuvant treatment for 3 years after surgery and who have a high risk of recurrence. In the first arm, patients will continue Imatinib treatment for 3 more years, allowing to determine if the continuation of this treatment is efficient for disease control, in terms of Disease Free Survival improvement. In the second arm, patients will discontinue the Imatinib treatment, as standard practice. This arm will allow to determine if the re-introduction of Imatinib at relapse is still an efficient treatment for the control of disease.

Gastrointestinal stromal tumours (GISTs) are rare mesenchymal neoplasms, mostly diagnosed between 55 and 60 years of age, which account for 5% of all sarcomas. Worldwide annual incidence is approximately 12 cases per million people, corresponding to approximately 800 new cases per year in France. A large majority of GISTs harbour activating mutations in the proto-oncogenes KIT and/or PDGFRA, both coding cell-surface cytokine receptors with tyrosine-protein kinase activity. Imatinib mesilate (Glivec®, Novartis Pharma SAS) is a selective tyrosine kinase inhibitor, leading to inhibition of KIT and PDGFRA signalling pathways. The introduction of imatinib has revolutionised the therapeutic management of GIST patients and has provided an unprecedented demonstration of the clinical benefit of a targeted therapy for patients with advanced/metastatic solid tumors. First results from prospective trials conducted with imatinib in GIST patients have demonstrated a 300% increase in median overall survival, and a likely 100% increase in 5 and 10-year survival as compared to cytotoxic chemotherapy. The successful use of imatinib in the treatment of advanced GISTs and the significant risk of recurrence of advanced GISTs have prompted the investigation of the clinical benefit of imatinib as a post-operative adjuvant therapy. Two prospective randomized Phase III trials have demonstrated that adjuvant imatinib treatment significantly prolong overall survival (OS) and recurrence-free survival (RFS) when given for 3 years. To date, imatinib is also indicated in the adjuvant setting after complete resection of primary, localized, KIT-positive GIST at high risk of recurrence. However, the optimal treatment duration remains unclear and it should be determined whether 1. prolonged use of adjuvant imatinib beyond 3 years may enable to reduce the risk of GIST recurrence and to improve overall survival, and 2. imatinib rechallenge is efficient for treating recurrence after completion of 3-year adjuvant imatinib therapy. This trial is an open-label, randomized, multicenter phase III study aiming to determine the clinical impact of maintaining imatinib treatment beyond 3 years in the adjuvant setting for patients with resected GISTs at high risk of recurrence according to the National Comprehensive Cancer Network Task Force on GIST (NCCN) risk classification.