55O IMADGIST: A randomized study of 6 vs 3 years of adjuvant imatinib in patients with localized GIST at high risk of relapse

Adjuvant imatinib is indicated after complete resection of primary, localized, KIT-positive GIST at high risk of recurrence. A large proportion of these patient relapse after the end of adjuvant imatinib. Whether prolonging adjuvant imatinib beyond 3 years may enable to reduce the risk of GIST recurrence has not been explored in a randomized setting. IMADGIST (NCT02260505) is a multicenter open-label, randomized, phase III study evaluating maintenance of imatinib at the last dose routinely taken by the patient in the 3-year period prior to randomization (either 300 or 400 mg/d) compared to Interruption of imatinib treatment (STOP arm) from the day of randomization. Primary endpoint is Disease-Free Survival (DFS). Secondary endpoints include Overall Survival, (OS) Time to Imatinib Resistance, Rate of Complete Response after reintroduction, Safety and Quality of Life. A sample size of 134 patients was calculated to detect an improvement of 15% in 3-year DFS rate (75% vs. 90% in the 3-years and 6-years arms, respectively). From December 24th, 2014 to April 4th, 2023; 136 patients aged ≥ 18, ECOG PS ≤2, with confirmed diagnosis of localized GIST with documented KIT (CD117) positivity, complete surgical R0 or R1, and a risk of tumor recurrence ≥35% according to National Comprehensive Cancer Network Task Force on GIST (NCCN) risk classification were randomised by 14 French anticancer centers. Sixty five patients were randomized to the 3-year arm vs 71 in the 6 year arm. 63 and 73 patients with moderate ([35-70%]) or high (>70%) NCCN risk, respectively, were included. The final analysis is scheduled for Janaury 31st, 2024. THe results will be presented at the congress. Data cut of was set to September 30th, 2023. Statistical analysis is in progress and results will be presented at the time of the congress.