TAMI-15. PROSTATE SPECIFIC MEMBRANE ANTIGEN EXPRESSION IN GLIOBLASTOMA TUMOR AND ENDOTHELIAL CELLS

Abstract

Abstract INTRODUCTION Prostate specific membrane antigen (PSMA) has emerged in recent years as a potential target for PET imaging of CNS tumors. Originally studied for imaging in prostate cancer, it was incidentally found to have selective uptake in some CNS tumors. Early studies have shown promise for PSMA tracer use in glioblastoma (GBM), but more research is needed to characterize the PSMA expression profile in GBM. METHODS Formalin-fixed paraffin-embedded tissues of 26 GBMs were immunostained with PSMA antibody. Stained sections were scored, using 5 images per tumor, in total 130 observations. Sections were assessed for extent and intensity of PSMA expression, in tumor cells and neovascular endothelial cells. Extent of expression: 0% (none), 1-9% (very low), 10-39% (low), 40-69% (moderate), > 70% (high). Intensity of expression: no staining (none); barely perceptible staining (low); readily apparent at low magnification (moderate); and maximum-intensity staining (high). RESULTS Extent of PSMA expression in tumor cells was mostly very low (76 out of 130, 58%), but intensity was often moderate (42, 32%), low (41, 32%), or high (39, 30%). The most prevalent combination was very low extent with low or moderate intensity (both 30, 23%). Endothelial cells were absent in 61 (47%) sections. Extent of expression in endothelial cells was mostly high (28, 41%), and intensity was often moderate (25, 36%) or high (20, 29%). The most prevalent combination was high extent with moderate (14, 20%) or high intensity (13, 19%). CONCLUSION PSMA expression was variable and was seen in both vascular endothelial cells and tumor cells. The mechanism of PSMA expression in GBM may not be straightforward, but rather may vary by cell type and tumor mutation status. Further tissue studies to understand the specific mechanism are needed to establish the potential use of PSMA PET as a neuroimaging modality in GBM.