Treatment Sequencing and Progression Management in IDH-Mutant Glioma

Dr. Cloughesy discusses treatment sequencing considerations when patients progress on vorasidenib. The INDIGO trial showed discrepancies between independent review progression and investigator-assessed time to next intervention, with investigators often waiting beyond formal progression criteria before initiating alternative treatments.

He draws parallels to other targeted therapies where continued treatment beyond progression may provide benefit due to slower tumor kinetics in resistant populations. Unlike radiation and chemotherapy which may promote more aggressive tumor biology through mutagenic effects, targeted therapy may select for slower-growing resistant clones.

This Darwinian selection hypothesis suggests that after achieving tumor control, resistant populations may grow more slowly than original tumors, potentially justifying continued treatment in some circumstances. However, clinical decisions must weigh continued benefit against emerging resistance.

For astrocytomas showing clear progression, he advocates moving expeditiously to radiation and chemotherapy, which remain the most effective treatments for overall survival despite associated cognitive risks. He's less enthusiastic about radiation or chemotherapy alone, preferring combined modality approaches.

Contrast enhancement development represents a concerning sign requiring immediate aggressive intervention with standard-of-care radiation and chemotherapy. The emergence of enhancing disease suggests transformation to more aggressive tumor biology necessitating prompt treatment escalation.

Future studies will help define optimal combination strategies and sequencing approaches as more IDH inhibitors become available. Understanding resistance mechanisms from the controlled INDIGO population will inform next-generation trial designs and combination therapy development.