INDIGO: vorasidenib, the first targeted drug for IDH-mutant low-grade glioma
An oral drug that blocks the mutant IDH enzyme more than doubled the time before slow-growing IDH-mutant brain tumours progressed, letting patients postpone radiotherapy and chemotherapy for years.
Double-blind, placebo-controlled phase 3 trial of 331 patients with residual or recurrent grade 2 IDH1- or IDH2-mutant oligodendroglioma or astrocytoma who had undergone surgery alone and were candidates for watch-and-wait, randomised to vorasidenib (a brain-penetrant dual IDH1/2 inhibitor) or placebo. Primary endpoint was PFS by blinded review.
Median PFS was 27.7 vs 11.1 months (HR 0.39) and the time to next intervention (radiotherapy or chemotherapy) was markedly delayed (HR 0.26). It was the first targeted therapy approved for glioma (FDA 2024) and the first drug to change the natural history of low-grade glioma, a disease of young adults where treatment toxicity accumulates over decades.
- Median PFS 27.7 vs 11.1 months; HR 0.39 (95% CI 0.27-0.56).
- Time to next intervention: HR 0.26 (95% CI 0.15-0.43); at 24 months, 83.4% vs 27.0% had not needed further treatment.
- Tumour growth rate was reversed in many patients, with volumetric shrinkage on vorasidenib versus continued growth on placebo.
- Grade 3 or higher adverse events 22.8% vs 13.5%, mainly raised liver enzymes (ALT increase in about 10%).
- Crossover from placebo to vorasidenib was allowed at progression; overall survival is not yet evaluable.
Young adults with a grade 2 IDH-mutant glioma who have had surgery can now take a daily tablet that slows or reverses tumour growth and defers radiotherapy and chemotherapy, both of which carry long-term cognitive costs, by years. It confirms that the IDH mutation is a driver that can be targeted, not just a marker. Whether it improves survival or cognition over the long term, and whether it helps in higher-grade or previously treated tumours, is unknown.
- PFS and time to next intervention are surrogates; overall survival data will take many years given the indolent disease.
- Only patients who had not received radiotherapy or chemotherapy were eligible; the drug's role after those treatments is undefined.
- Liver toxicity requires regular monitoring.
- Indefinite treatment of young patients is costly, and stopping rules are not established.
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