Early volumetric, perfusion, and diffusion MRI changes after mutant isocitrate dehydrogenase (IDH) inhibitor treatment in IDH1-mutant gliomas.

Background: Inhibition of the isocitrate dehydrogenase (IDH)-mutant enzyme is a novel therapeutic target in IDH-mutant gliomas. Imaging biomarkers of IDH inhibitor treatment efficacy in human IDH-mutant gliomas are largely unknown. This study investigated early volumetric, perfusion, and diffusion MRI changes in IDH1-mutant gliomas during IDH inhibitor treatment.

Methods: Twenty-nine IDH1-mutant glioma patients who received IDH inhibitor and obtained anatomical, perfusion, and diffusion MRI pretreatment at 3-6 weeks ( = 23) and/or 2-4 months ( = 14) of treatment were retrospectively studied. Normalized relative cerebral blood volume (nrCBV), apparent diffusion coefficient (ADC), and fluid-attenuated inversion recovery (FLAIR) hyperintensity volume were analyzed.

Results: After 3-6 weeks of treatment, nrCBV was significantly increased ( = .004; mean %change = 24.15%) but not FLAIR volume ( = .23; mean %change = 11.05%) or ADC ( = .52; mean %change = -1.77%). Associations between shorter progression-free survival (PFS) with posttreatment nrCBV > 1.55 ( = .05; median PFS, 240 vs 55 days) and increased FLAIR volume > 4 cm ( = .06; 227 vs 29 days) trended toward significance. After 2-4 months, nrCBV, FLAIR volume, and ADC were not significantly different from baseline, but an nrCBV increase > 0% ( = .002; 1121 vs 257 days), posttreatment nrCBV > 1.8 ( = .01; 1121 vs. 270 days), posttreatment ADC < 1.15 μm/ms ( = .02; 421 vs 215 days), median nrCBV/ADC ratio increase > 0% ( = .02; 1121 vs 270 days), and FLAIR volume change > 4 cm ( = .03; 421 vs 226.5 days) were associated with shorter PFS.

Conclusions: Increased nrCBV at 3-6 weeks of treatment may reflect transient therapeutic and/or tumor growth changes, whereas nrCBV, ADC, and FLAIR volume changes occurring at 2-4 months of treatment may more accurately reflect antitumor response to IDH inhibition.