Long-term results from a trial comparing adjuvant imatinib treatment to observation after R0/R1 surgery for gastrointestinal stromal tumour (GIST) support the recommendation to administer imatinib in this setting only in patients with high-risk GIST, researchers reported at ESMO 2017, the Annual Congress of the European Society for Medical Oncology in Madrid, Spain.
Patients with low to intermediate risk GIST did not derive additional benefit with imatinib compared to observation.
Lead author Paolo G.G. Casali, of the Adult Mesenchymal Tumour and Rare Cancer Medical Oncology Unit, Fondazione IRCCS - Istituto Nazionale dei Tumori in Milan, Italy presented final results on behalf of colleagues from an intergroup randomised trial (EUDRACT 2004-001810-16, NCT00103168) of adjuvant imatinib versus no further therapy in patients with localised, high/intermediate-risk GIST following R0-R1 surgery.
The results of the interim analyses, which was performed upon recommendation from an independent data review committee have been previously reported.1 The interim analysis concluded that the data confirmed that adjuvant imatinib had an overt impact on relapse-free survival (RFS). No significant difference in imatinib failure-free survival (IFFS) was demonstrated, although a trend in favour of adjuvant imatinib was observed in the high-risk subgroup.
This final analysis was done on data from a randomised, open label, multicentre phase III trial that took place at 112 hospitals in 12 countries. Patients were randomised to 2 years of imatinib at 400 mg daily, or no further therapy after surgery.
The primary end-point was IFFS, with secondary endpoints of RFS, relapse-free interval (RFI), overall survival (OS) and toxicity. Adjusting for the interim analyses, results on IFFS were assessed at a 4.3% significance level and the other endpoints used 5%.
A total of908 patients were randomised from December 2004 to October 2008, with 454 receiving imatinib and 454 receiving observation; of these 835 patients were eligible for analysis.
Subgroup of patients with high risk GIST demonstrates a trend towards improved long-term imatinib failure-free and relapse-free survival
After long-term follow-up of a median 9.1 years, the 5- and 10-year IFFS rates were 87% and 75% in the imatinib arm versus 83% and 74% in the observation-only control arm, respectively, hazard ratio [HR] 0.87; 95.7% confidence interval [CI] 0.65, 1.15 (p = 0.31). In the respective arms, RFS was 70% versus 63% at 5 years and 63% versus 61% at 10 years, HR 0.71; 95% CI 0.57, 0.89 (p = 0.002).
The 5-year OS rates with imatinib versus controls were 93% versus 92% and the 10-year OS rates were 80% versus 78%, respectively, HR 0.88; 95% CI 0.65, 1.21 (p = 0.43).
Among 526 patients with high-risk GIST by local pathology, the 10-year IFFS rates were 69% versus 61%, and the 10-year RFS rates were 48% versus 43% in the imatinib versus observation arms, respectively.
The authors noted that a trend toward better long-term IFFS and RFS was observed after 9.1 years of follow-up in imatinib-treated patients in the subgroup of patients having high-risk GIST.
They pointed out that, while not statistically significant, this trend is consistent with the results reported by the Scandinavian/German trial, which demonstrated a sustained small but significant long-term OS benefit in high-risk GIST patients treated with 3 years of adjuvant imatinib.
The investigators advised that findings from the study presented at ESMO 2017 discourage the use of imatinib in patients affected by lower risk GIST, per current standards, since the long-term IFFS and RFS rates between the imatinib and observation only arms were comparable and superimposable.
This study was funded by Novartis.
- Casali PG, et al. Time to definitive failure to the first tyrosine kinase inhibitor in localized GI stromal tumors treated with imatinib as an adjuvant: a European Organisation for Research and Treatment of Cancer Soft Tissue and Bone Sarcoma Group intergroup randomized trial in collaboration with the Australasian Gastro-Intestinal Trials Group, UNICANCER, French Sarcoma Group, Italian Sarcoma Group, and Spanish Group for Research on Sarcomas. JCO 2015;33(36):4276—4283.
LBA55 – Casali PGG, et al. Time to definitive failure to the first tyrosine kinase inhibitor in localized gastrointestinal stromal tumors (GIST) treated with imatinib as an adjuvant: final results of the EORTC STBSG, AGITG, UNICANCER, FSG, ISG, and GEIS randomized trial.