Background
Phase III double-blind RCT. 713 adults with a completely resected, KIT-positive primary GI GIST at least 3 cm in maximal diameter. Adjuvant TKI strategy in resected localized GIST was unproven at the time.
Interventions and follow up
Arm A: imatinib 400mg daily for 1yr (n=359)
Arm B: placebo (n=354); trial stopped early after significantly fewer recurrences in the imatinib arm, placebo patients allowed crossover
Primary endpoint: Recurrence-free survival (RFS)
mFollow up: 20mo
Arm B: placebo (n=354); trial stopped early after significantly fewer recurrences in the imatinib arm, placebo patients allowed crossover
Primary endpoint: Recurrence-free survival (RFS)
mFollow up: 20mo
Results
1-yr RFS: 98% vs 83%, HR 0.35, 95%CI 0.22-0.53; P<.0001
OS: no significant difference (98.7% vs 99.2%)
RFS by tumor size 3-6 cm: no significant difference
RFS by tumor size 6-10 cm: HR 0.05, favoring imatinib
RFS by tumor size ≥10 cm: HR 0.29, favoring imatinib
OS: no significant difference (98.7% vs 99.2%)
RFS by tumor size 3-6 cm: no significant difference
RFS by tumor size 6-10 cm: HR 0.05, favoring imatinib
RFS by tumor size ≥10 cm: HR 0.29, favoring imatinib
Adverse events
Grade 3-4 (imatinib vs placebo): overall higher with imatinib but discontinuation for toxicity uncommon
GI / constitutional: nausea, diarrhea, fatigue
Dermatologic: rash / dermatitis more frequent with imatinib
Edema: more frequent with imatinib; profile consistent with established imatinib toxicity
GI / constitutional: nausea, diarrhea, fatigue
Dermatologic: rash / dermatitis more frequent with imatinib
Edema: more frequent with imatinib; profile consistent with established imatinib toxicity
Conclusions
1 year of adjuvant imatinib significantly prolonged RFS after complete resection of primary KIT-positive GIST, establishing adjuvant TKI therapy in this setting.
Key Limitations
Short median follow-up (20mo) with early stopping inflates the RFS benefit; placebo crossover and a curative-intent population obscure any OS signal; benefit concentrated in larger/higher-risk tumors with no clear gain for 3-6 cm tumors; optimal duration not addressed (later answered by SSG XVIII).
Clinical Context
Z9001 led to FDA approval (2008) of adjuvant imatinib for KIT-positive resected GIST. ESMO and ASCO endorse adjuvant imatinib for significant-risk resected GIST. Duration was subsequently extended to 3 years for high-risk disease based on SSG XVIII; mutational status (e.g., PDGFRA D842V, low-risk small tumors) refines patient selection.
References