Patterns of radiological response to PC polychemotherapy in patients with oligodendroglioma

PURPOSE To characterize the radiological response to procarbazine and CCNU (PC) polychemotherapy in patients with oligodendroglioma. METHODS In this retrospective single-centre cohort study, patients with 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 < 0.01). Stratification according to CNS WHO grade (p = 0.89) or contrast enhancement (p = 0.07) did not yield significant differences. The T1/T2 ratio was lower after PC (0.69 vs 0.50, p = 0.04), and higher T1/T2 ratios were associated with shorter PFS (p = 0.04) in multivariate analysis. On [18F]FET PET, there was a trend towards lower maximum tumor-to-brain ratios (TBRmax) after PC (p = 0.07). 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.