Patterns of radiological response to procarbazine and CCNU polychemotherapy in patients with oligodendroglioma.

PURPOSE: To characterize the radiological response to procarbazine and CCNU (chloroethyl-cyclohexyl-nitrosourea) (PC) polychemotherapy in patients with oligodendroglioma. METHODS: In this retrospective single-center cohort study, patients with Central Nervous System World Health Organization (CNS WHO) grade 2 or 3 oligodendroglioma treated with PC between 2003 and 2019 were included. Tumor characteristics were assessed on magnetic resonance imaging (MRI) and [18F]Fluoroethyltyrosine positron emission tomography ([18F]FET PET) before and after completion of PC. The T1/T2 ratio was assessed to characterize diffuse versus sharply delineated MRI phenotype. Progression-free survival (PFS) and overall survival (OS) were analyzed. RESULTS: Forty-six patients with a median follow-up of 118 months were identified. Median absolute T2 tumor volume was 52 cm³ (range 10-285) prior to PC and 29 cm³ (range 3-286) after. Median tumor volume decrease was -30% (range -96% to +113%). In treatment-naïve patients, median tumor volume decrease was -41% (range -92% to +14%) versus -7% (range -96% to +113%) in pretreated patients (P < .01). Stratification according to CNS WHO grade (P = .89) or contrast enhancement (P = .07) did not yield significant differences. The T1/T2 ratio was lower after PC (0.69 vs 0.50, P = .04), and higher T1/T2 ratios were associated with shorter PFS (P = .04) in multivariate analysis. On [18F]FET PET, there was a trend towards lower maximum tumor-to-brain ratios (TBRmax) after PC (P = .07). CONCLUSION: PC polychemotherapy induces substantial tumor volume reductions in subsets of patients with oligodendroglioma, particularly in treatment-naïve patients. The observations that circumscript oligodendrogliomas may be associated with earlier progression and that PC treatment may induce a shift toward a more diffuse phenotype require prospective validation.