EVALUATING METABOLIC ALTERATIONS IN PATIENTS WITH EGFR ACTIVATED RECURRENT GLIOBLASTOMA (RGBM) BY INHIBITING EGFR WITH OSIMERTINIB

Abstract BACKGROUND EGFR activated GBM is highly metabolically active and effective targeting with EGFR TKis in human-tumor models rapidly attenuates glucose metabolism engaging apoptotic machinery. Rapid changes in glucose uptake using 18F-FDG-PET is an effective predictive biomarker of therapeutic response in these models. Clinical 18F-FDG-PET may allow investigators to obtain early readout on EGFR TKi in this patient population. We explore this approach using osimertinib in EGFRamp/p53wt rGBM. METHODS EGFRamp/p53wt rGBM patients were treated with oral osimertinib 240mg for three days followed by 160mg/day until progression. F18-FDG-PET scan was obtained as a double baseline, 24 hours apart, prior to dosing with osimertinib. Third scan was obtained after 3 doses of 240mg. Primary objective defines test-retest variance of tumor FDG uptake before osimertinib and to evaluate if osimertinib significantly decreases glucose utilization after three doses. Study-drug and funding provided by AstraZeneca. RESULTS 12 pts were evaluated, 10 female, median age 57.5 years (44-61). Volumetric mRANO showed no responses, 6 SD, 5 PD, and one NE. Median PFS was 31 days, no patient achieved 6-month-PFS and median OS was 5.5 months. No new adverse event signal appeared. Double baseline PET SUV mean was 0.97 (normalized to whole cerebellum) with upward trend from first to second scan with mean percent change of 2.8 and 95% CI(0.7,5.1). Change in PET from 2nd to 3rd showed mean percent change -3.2 with 95% CI (-11.1,4.8). Preclinical models suggest 15-20% attenuation is needed to predict improved outcomes in patients treated with EGFR-TKi. CONCLUSION F18-FDG-PET has little variance with test-retest showing upward trend with second scan. Post osimertinib F18-FDG-PET shows limited attenuation of tumor FDG uptake. No clinical signal was seen in study. Deeper attenuation of FDG uptake may be needed to show clinical effect from EGFR inhibitors. F18-FDG-PET can be used to evaluate change in tumor glucose utilization.