NI-13 Prediction of outcome at the time of discontinuing TMZ-adjuvant therapy in IDH-mutant lower grade glioma using (11)C-methinine PET

Purpose: This study aimed to clarify whether positron emission tomography with (11)C-methyl-L-methionine ((11)C-met PET) can predict consequential outcomes at the time of discontinuing temozolomide (TMZ)-adjuvant chemotherapy in patients with residual isocitrate dehydrogenase gene (IDH)-mutant lower-grade glioma.Methods: In 30 patients showing residual lesions of IDH-mutant lower grade glioma (16 with diffuse astrocytoma and 14 with anaplastic astrocytoma), we performed (11)C-met PET, and calculated the tumor-to-normal brain tissue ratio of standardized uptake values (SUV(T/N)) at the time of discontinuing TMZ-adjuvant chemotherapy. We determined cutoff values to predict tumor relapse using the receiver operating characteristic curve for various prognostic factors including age, Karnofsky performance scale, number of courses of therapy, residual tumor size, and SUV(T/N). The promotor methylation status of O(6)-methylguanine-DNA methyl-transferase gene (MGMT) was assessed using methylation-specific polymerase chain reaction. Progression-free survival (PFS) was compared between groups divided by cutoff values. Uni- and multivariate analyses were conducted using log-rank testing and Cox regression analysis, respectively.Results: Univariate analysis identified MGMT methylation status (p = 0.04) and an SUV(T/N) of 1.27 (p = 0.02) as predictors of PFS after TMZ discontinuation. In multivariate analysis, both unmethylated MGMT and SUV(T/N) ≥ 1.27 remained as strong predictors of unfavorable outcome. Conclusion: The present study suggested that (11)C-met PET allows prediction of outcomes comparable to MGMT promotor methylation status at the time of discontinuing TMZ-adjuvant chemotherapy in patients with residual IDH-mutant lower-grade glioma.