Distinguishing Tumor from Post-Surgical Changes in Patients with IDH-Mutant Glioma

Fourteen months into vorasidenib therapy, the patient remains clinically stable and seizure-free with continued work. Recent MRI shows stable T2-FLAIR signal without enhancement or measurable shrinkage. Transient liver function test elevations to 2.5 times upper limit of normal resolved after temporary dose hold.

Dr. Cloughesy addresses the critical question of whether the drug is working despite stable imaging appearance. The absence of tumor growth represents success, given that placebo patients experienced 25% tumor progression by 11 months and 14% growth every 6 months based on study data.

Tumor shrinkage occurs gradually over time, with waterfall plots showing increasing numbers of patients demonstrating tumor regression with extended follow-up. Visual detection of subtle changes can be challenging, particularly when comparing only recent scans rather than baseline measurements.

The patient's clinical stability (absence of seizures, maintained function, stable imaging) represents optimal outcomes. These tumors naturally grow without intervention, so preventing growth while maintaining quality of life demonstrates treatment efficacy.

Important imaging considerations include differentiating post-surgical scarring from tumor recurrence. Scarring typically shows curvilinear enhancement respecting surgical cavity margins, while tumor demonstrates nodular enhancement with infiltrative patterns. Non-enhancing changes require assessment of cortical ribbon involvement, as scarring respects anatomical boundaries whereas tumors infiltrate beyond them.

Expansile effects causing tissue gain suggest tumor growth, while scarring typically produces tissue loss. New seizure activity during imaging changes strongly suggests tumor rather than scarring. These subtle distinctions require experienced interpretation and consistent imaging protocols.