P09.14.B PREDICTION OF BEVACIZUMAB EFFICACY IN RECURRENT GLIOBLASTOMA PATIENTS BY EVALUATING [18F]-FET PET IMAGING RESPONSE
Authors: Chiranth S B , Henriksen O M , Hasselbalch B , Grunnet K , Carlsen J F , Poulsen H S , Law I , Urup T , Madsen K 
Published: October 2024

Abstract

BACKGROUND
Glioblastoma (GBM) is the most common malignant primary brain tumor in adults. Despite aggressive treatment, the prognosis is poor with a median overall survival (OS) of 16 months. Bevacizumab combination therapy has shown response in approximately 25% of recurrent GBM patients. However, due to its effect on the tumor vasculature and contrast distribution, it is challenging to assess response using a conventional contrast-enhanced MRI. The goal of this study was to assess the value of [18F]-FET PET imaging for response evaluation in recurrent GBM patients treated with bevacizumab combination therapy. We aim to use these findings to more effectively select patients who would benefit from this treatment.

MATERIAL AND METHODS
All recurrent GBM (IDHwt) patients treated with bevacizumab plus irinotecan at Rigshospitalet (Denmark) and evaluated with paired [18F]-FET PET imaging from April 2018 to February 2022 were included. MRI and [18F]-FET PET imaging was performed at baseline and after 2 cycles of treatment. [18F]-FET PET imaging was performed as a 20 min scan starting approximately 20 min after 200 MBq [18F]-FET was injected intravenously, and the metabolic tumor volumes (MTV) and maximum tumor/brain ratios (TBR) were measured. Data will be analyzed using the receiver operating curve (ROC) analysis to determine thresholds for response. Subsequently, the predictive capability of [18F]-FET PET thresholds in assessing treatment efficacy will be evaluated using uni- and multivariate Cox regression analysis modelling OS, defined here as time from start of treatment to death.

RESULTS
A total of 86 patients with recurrent GBM (IDHwt) who were treated with bevacizumab/irinotecan were included. The median age in the population was 58 years (range: 21-77) with males comprising 58% of the group. There was an MGMT methylation rate of 32% and 15% of the cohort had multifocal disease. Most patients were in good ECOG performance status 0-1 (88%) and 46% of the cohort received steroid treatment at baseline. The median OS in the cohort was 9 months (95% CI: 7.7-10.3 months). At the time of recurrence, all patients received baseline [18F]-FET PET imaging up to 4 weeks prior to receiving combined bevacizumab treatment. Follow-up [18F]-FET PET imaging was conducted within 16 weeks of start of treatment in 81 patients after receiving 2 cycles of treatment. Using the data from the scans, the patients will be classified as responders and non-responders and the predictive capability of [18F]-FET PET thresholds will be compared.

CONCLUSION
The final results will be presented at the conference. We aim to use our findings about the predictive capability of [18F]-FET PET imaging to more precisely identify responders and non-responders among recurrent GBM patients treated with bevacizumab combination therapy. Thus, enabling us to more effectively select patients who would benefit from this treatment.