MetaGIST group trial

Background

Meta-analysis of individual patient data from two large phase III trials (EORTC 62005 and US Intergroup S0033/CALGB) comparing imatinib 400mg/day vs 800mg/day in 1,640 patients with unresectable or metastatic GIST, pooled to clarify the dose question and mutation-specific effects.

Interventions and follow up

Comparison: imatinib 400mg/day vs 800mg/day, pooled from EORTC 62005 and S0033
Primary endpoint: Progression-free survival (PFS); secondary OS and response
mFollow up: 45mo

Results

PFS: small but significant advantage for 800mg/day, HR 0.89, 95%CI 0.79-1.00
OS: no significant difference between doses
Best response: 51% vs 54%, similar across doses
KIT exon 9 subgroup: 800mg/day improved PFS (but not OS); benefit of high dose concentrated in exon 9-mutant tumors

Adverse events

Pooled toxicity: 800mg/day associated with more frequent and more severe adverse events than 400mg/day
Common with higher dose: anemia, fatigue, edema, diarrhea, with more dose reductions and interruptions

Conclusions

Imatinib 800mg/day yields a small PFS advantage but no OS benefit over 400mg/day overall; the gain is driven by KIT exon 9-mutant tumors, supporting mutation-guided first-line dosing.

Key Limitations

Subgroup mutation analyses are exploratory and limited by incomplete genotyping; both source trials allowed crossover, biasing the OS comparison; the exon 9 conclusion rests on a small subset; pooling assumes comparable trial designs and endpoints.

Clinical Context

MetaGIST cemented mutation-guided first-line imatinib dosing in advanced GIST: 400mg/day standard, 800mg/day for KIT exon 9-mutant tumors, an approach endorsed by ESMO and reflected in ASCO guidance. It established the role of routine genotyping at diagnosis of advanced GIST.

References