NIMG-26. UPTAKE OF [¹⁸F]GE-180 IN TSPO PET IS ASSOCIATED WITH SURVIVAL IN PATIENTS WITH RECURRENT GLIOMA

The 18 kDa translocator protein (TSPO) is expressed in both activated microglia and glioma cells. Elevated expression of TSPO has been reported to be associated with higher WHO grade. Here we analyze whether TSPO positron emission tomography (PET) signal using the tracer [¹⁸F]GE-180 is correlated with clinical outcome in a cohort of patients with recurrent glioma.

Patients with suspected glioma recurrence received a [¹⁸F]GE-180 TSPO PET. All recurrent tumors were confirmed either by stereotactic biopsy or resection. Maximum standard uptake value SUV_max as well as tumor volume in MRI and, if available, in [¹⁸F]FET PET were evaluated together with patient characteristics (age, sex, Karnofsky-Performance score) and neuropathological features (WHO grade, IDH-mutation status). Uni- and multivariate Cox regression and Kaplan-Meier survival analyses were performed to identify prognostic factors for post-recurrence survival (PRS) and time to treatment failure (TTF).

88 consecutive patients were evaluated. TSPO tracer uptake correlated with tumor grade at recurrence (p< 0.05), with no significant differences between IDH-wildtype and IDH-mutant tumors. Within the subgroup of IDH-mutant glioma (n= 46), patients with low SUV_max (median split, ≤ 1.60) had a significantly longer PRS (median 41.6 vs. 25.3 months, p= 0.031) and TTF (32.2 vs 8.7 months, p= 0.001). Also among IDH-wildtype tumors (n= 42), patients with low SUV_max (≤ 1.89) had a significantly longer PRS (median not reached vs 8.2 months, p= 0.002). SUV_max remained an independent prognostic factor for PRS in a multivariate analysis including WHO grade, IDH status and age. Tumor volume defined by [¹⁸F]FET PET or contrast-enhanced MRI correlated weakly with TSPO tracer uptake. Treatment regimen did not differ between the subgroups.

Our data suggest that uptake of [¹⁸F]GE-180 in TSPO PET can add prognostic information in patients with recurrent glioma even in molecular defined subgroups and might serve as an imaging biomarker.