Final analysis of the randomized trial on imatinib as an adjuvant in localized gastrointestinal stromal tumors (GIST) from the EORTC Soft Tissue and Bone Sarcoma Group (STBSG), the Australasian Gastro-Intestinal Trials Group (AGITG), UNICANCER, French Sarcoma Group (FSG), Italian Sarcoma Group (ISG), Spanish Group for Research on Sarcomas (GEIS)

P G Casali, A Le Cesne, A Poveda Velasco, D Kotasek, P Rutkowski, P Hohenberger, E Fumagalli, I R Judson, A Italiano, H Gelderblom, N Penel, J T Hartmann, F Duffaud, D Goldstein, J Martin Broto, A Gronchi, E Wardelmann, S Marréaud, J R Zalcberg, S Litière, J-Y Blay
Annals of Oncology: Official Journal of the European Society for Medical Oncology 2021 January 19

BACKGROUND: In 2004, we started an intergroup randomized trial of adjuvant imatinib versus no further therapy after R0-R1 surgery in localized, high/intermediate-risk GIST patients. Interim analysis results were published in 2015 upon recommendation from an independent data review committee. We report the final outcome of the study.

METHODS: This was a randomized, open label, multicenter phase III trial performed at 112 hospitals in 12 countries. Patients were randomized to 2 years (yrs) of imatinib, 400 mg daily, or no further therapy after surgery. The primary end-point was imatinib failure-free survival (IFFS), while relapse-free survival (RFS), relapse-free interval (RFI), overall survival (OS) and toxicity were secondary end-points. Adjusting for the interim analyses, results on IFFS were assessed on a 4.3% significance levels; for the other endpoints, 5% was used.

RESULTS: 908 patients were randomized between January 2005 and October 2008, 454 to imatinib and 454 to observation. 835 patients were eligible. With a median follow-up of 9.1 years, 5 (10)-year IFFS was 87% (75%) in the imatinib arm versus 83% (74%) in the control arm (HR=0.87, 95.7% CI [0.65; 1.15], p=0.31); RFS was 70% versus 63% at 5 years and 63% vs 61% at 10 years, (HR=0.71, 95% CI [0.57; 0.89], p=0.002); OS was 93% versus 92% at 5 years and 80% versus 78% at 10 years (HR=0.88, 95% CI [0.65; 1.21], p=0.43). Among 526 patients with high-risk GIST by local pathology, 10-year IFFS and RFS were 69% versus 61%, and 48% versus 43%, respectively.

CONCLUSIONS: With 9.1 years of follow-up, a trend toward better long-term IFFS in imatinib-treated patients was observed in the high-risk subgroup. Although the difference was not statistically significant and the surrogacy value of such an end-point is not validated, this may be seen as supporting the results reported by the Scandinavian/German trial, showing a sustained small but significant long-term OS benefit in high risk GIST patients treated with 3 years of adjuvant imatinib.

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