[18F]SiTATE PET for PRRT selection and monitoring metastatic tumors of the adrenal medulla and extra-adrenal paraganglia.

PURPOSE In somatostatin receptor (SSTR)-expressing tumors, theranostics with SSTR-directed imaging and therapy showed promising results regarding disease control. This study evaluated the use of PET imaging with [18F]SiTATE in pheochromocytoma and paraganglioma (PPGL) patients, focusing on eligibility for peptide radioreceptor therapy (PRRT) and therapy monitoring. METHODS Five patients with metastatic paraganglioma (n = 3) or pheochromocytoma (n = 2) were included. Eligibility for PRRT was assessed by [18F]SiTATE applying the Krenning score and baseline SUVmax. Treatment response was analyzed by RECIST 1.1 criteria, total tumor volume (PET-based TTV), and Chromogranin A (CgA). RESULTS At baseline, all patients showed high lesional uptake, with the highest in the bone (mean SUVmax 41.4 ± 87.3) and a high Krenning Score of 3-4, Suggestive for PRRT eligibility. At the follow up, 2.5 months after completion of PRRT, all patients presented with stable disease (RECIST 1.1) and decreasing or stable CgA levels, whereas TTV increased in three patients and thus showed heterogenous response. CONCLUSION In metastatic PPGL, [18F]SiTATE effectively visualizes tumor burden and supports patient selection and response assessment for PRRT. Notably, the data revealed a heterogenous response across PET-based, CT-based, and biochemical assessments. The underlying mechanisms of these discrepancies remain unclear and warrant further investigation.