Randomized phase III trial of imatinib (IM) rechallenge versus placebo (PL) in patients (pts) with metastatic and/or unresectable gastrointestinal stromal tumor (GIST) after failure of at least both IM and sunitinib (SU): RIGHT study.

Abstract

LBA10502 Background: To palliate and prolong disease control after failure of all available treatment in advanced GIST, resumption of IM dosing has been commonly practiced based on evidence of rapid GIST progression after discontinuation of all TKIs. We evaluated the efficacy of IM rechallenge in pts with advanced GIST following failure of all TKIs. Methods: Eligible pts had metastatic and/or unresectable GIST with prior benefit from first-line IM (defined as disease control for > 6 months), progressive disease (PD) on first-line IM, PD on or intolerance to SU, and ECOG performance status 0-3. Pts were randomized 1:1 to receive best supportive care with either IM 400 mg po once daily or PL. At the time of PD, pts were unblinded and allowed to cross-over to open-label IM. The primary endpoint was progression-free survival (PFS) determined by blinded external radiology review according to RECIST v1.0. Secondary endpoints included overall survival (OS), time to progression, disease control rate (DCR) at 12 weeks, and safety. Results: Between July 2010 and January 2013, 81 pts were randomized (IM: 41, PL: 40) at a single Korean center. All baseline characteristics were balanced between the arms and 40% of pts received ≥ 3 prior TKIs. The planned final analysis in March 2013 demonstrated that the primary endpoint was met, with significantly greater PFS for pts randomized to IM vs. PL : 1.8 vs. 0.9 months, respectively (p=0.002), hazard ratio (HR) 0.45 (95% CI, 0.27-0.76). DCR at 12 weeks was 32% for IM vs. 5% for PL (p=0.003). With 92.5 % of PL pts rapidly crossing over to IM, median OS was 8.2 months for IM vs. 7.5 months for PL (HR of 0.99, p=0.982). The most common treatment-emergent AEs (> grade 3) during double-blind period in the IM arm included anemia (29%), fatigue (10%), and hyperbilirubinemia (7%). Conclusions: Rechallenge of IM significantly improves PFS and DCR in pts with advanced GIST after failure of at least IM and SU, likely by continuous kinase inhibition of the bulk of disease clones which retain IM sensitivity. However, TKI-resistant clones continue to progress leading to relatively brief duration of benefit. Clinical trial information: NCT01151852.