Ga-68-Edotreotide PET/CT SSTR Total Tumor Volume as a Predictor of Outcome in Patients With Metastatic Gastroenteropancreatic Neuroendocrine Tumors

IntroductionThe somatostatin receptor (SSTR) standardized uptake value (SUVmax_sstr) obtained by [⁶⁸Ga]Ga-edotreotide positron emission tomography-computed tomography ([⁶⁸Ga]Ga-SSTR PET/CT) helps recognize patients with metastatic gastroenteropancreatic neuroendocrine tumors (GEP-NETs) who are at a high risk for adverse outcomes. This observational cohort study was conducted to verify whether the SSTR representative tumor volume (RTV_sstr) can provide incremental prognostic information over conventional PET/CT parameters in patients with metastatic disease.MethodsWe retrospectively evaluated patients (48% female) with metastatic GEP-NETs who underwent [⁶⁸Ga]Ga-SSTR PET/CT between January 2022 and November 2023. The mean SUVmax_sstr, mean RTV_sstr (cm³; 42% threshold), and total RTV_sstr were recorded. Thereafter, patients were followed up for 22.9 (range: 8-42) months. The PET/CT results were compared to the progression free survival (PFS).ResultsSixty patients (59 ± 5 years) were enrolled. Only the mean and total RTV_sstr values were predictive in the multivariate analysis. Kaplan-Meier survival analysis for both the mean and total RTV_sstr demonstrated a significantly better PFS in patients presenting with lower than greater values (<i>P</i> = 0.001 and <i>P</i> = 0.007, respectively; log-rank test). SUVmax_sstr was not appropriate for predicting PFS.ConclusionThe mean or total RTV_sstr represents a valuable volumetric parameter able to predict outcomes in patients with GEP-NETs that are metastatic at onset. The degree of the SSTR representative tumor burden, rather than the maximal SSTR representation at single voxel, has a predominant value for influencing the response to therapy in this cohort.