10174-CS-18 Upfront chemotherapy and subsequent resection utilizing neoadjuvant chemotherapy for oligodendrogliomas

Abstract Functional preservation and maximal resection are both critical in glioma surgery, however, neoadjuvant chemotherapy has not been utilized so far. Although IDH-mutant and 1p/19q-codeled oligodendroglioma is known as relatively indolent tumor, the great majority of the patients eventually succumbs to death over 20 years. Because peak incidence of oligodedrogliomas is in 30s to 40s, long-term survival rate as well as functional preservation during the period is to be improved. In Keio University Hospital, oligodendrolgiomas have been treated utilizing neoadjuvant strategy since 2006; patients with 1p/19q-codeled oligodendroglioma were treated with upfront chemotherapy, and, for the cases with initial incomplete resection, a second-look resection (SLR) was intended following tumor volume decrease by chemotherapy (J Neurooncol 124:127-35, 2015, J Neurooncol 155:235-246, 2021, Brain Tumor Pathol 41:43-49, 2024). Moreover, for cases predicted to have oligodendrogliomas based on preoperative images, intentional staged resection was performed. We report the preliminary results of this prospective, observational study. Forty-seven (G2: 35, G3: 12) oligodendroglioma patients with no prior history of radiotherapy or chemotherapy were treated with the above mentioned strategy. Radiotherapy was given following chemotherapy or SLR in 11 cases. In 36 cases with initial incomplete resection, the median tumor volume decrease by chemotherapy was 31%, and SLR was performed in 24 cases. The median PFS/OS in the 40 newly diagnosed cases were 92 months/not reached, while those in the 30 patients with radiotherapy deferred were 99 months/not reached. Most tumor recurrence occurred within residual FLAIR abnormality. Staged resection strategy utilizing neoadjuvant chemotherapy might offer 1) more precise and safe resection as compared with traditional one-time resection, 2) information regarding necessity of radiotherapy based on presence/absence of residual FLAIR abnormality, 3) greater chance of complete resection due to possible regression of invading front. Preoperative prediction of 1p/19q-codeletion based on imaging features is encouraged.