Context Despite the growing evidence of the clinical value of somatostatin receptor (SSTR) PET in the evaluation of neuroendocrine tumors/NET, its role remains to be clarified at different time points in the MEN1 patient journey. The rareness of the disease is however a significant impediment to prospective clinical trials. Objectives The goals of the study were to assess the indications and value of SSTR PET/CT in MEN1 patients. Methods We retrospectively included patients from 7 French expert centres for whom data on SSTR PET/CT and morphological imaging performed at the same period were available. Detection rates of PET study were analysed. Results One hundred eight patients were included. SSTR PET/CT was performed at screening (n=33), staging (n=34), restaging (n=37) and for PRRT selection (n=4). PET detected positive pancreatic lesions in 91% of cases at screening, with comparable results to MRI but superiority to CT (P=0.049). Metastases (mostly LN) were present at the screening phase in 28% of cases, possibly due to the suboptimal value of screening morphological imaging in the assessement of nodal metastases and/or a long delay between imaging studies. SSTR PET/CT was considered as superior or complementary to the reference standard in the assessment of LN or distant metastases in the vast majority of cases and regardless of the clinical scenario. Conclusion This study shows the potential added value of SSTR PET in the assessment of MEN1-associated NETs and provides a great impetus towards its implementation in the evaluation of MEN1 patients.

Background Minimally invasive parathyroidectomy (MIP) has gained acceptance as the preferred surgical procedure for management of primary hyperparathyroidism (pHPT). Appropriate selection of patients for a MIP is a crucial step in its utilization. The aim of the study was to evaluate the role of 18 F-FCH PET/CT as second-line imaging for accurately directing MIP. Methods This is a retrospective single-center study. Seventy-two patients with biochemical evidence of pHPT and a non-conclusive or negative first-line imaging (ultrasound and dual isotope subtraction scintigraphy) received 18 F-FCH PET/CT between January 2018 and February 2020. All imaging studies were performed at our institution. Assessment of therapeutic changes and outcomes was performed. Results of the 72 patients imaged with 18 F-FCH PET/CT, 54 subsequently underwent parathyroidectomy. When considering the ability of 18 F-FCH PET/CT alone to predict a uniglandular disease, the sensitivity, specificity, PPV and NPV were 92.7% (95%CI: 80.1-98.5), 46.2% (19.2-74.9), PPV 87.3% (80.5-92) and NPV 61.2% (31.4-84.5), respectively. When we combined the data provided by 18 F-FCH PET/CT with the data already collected from 1 st line imaging we were able to complete a minimally invasive surgery in 38 of the 41 (92%) patients with a uniglandular disease. Thirteen patients (24%) had a multiglandular disease, all of them except one underwent bilateral neck exploration based on the data collected by all imaging modalities combined. Overall, cure was achieved in 53 (98%) patients. Conclusion 18 F-FCH PET/CT, interpreted along with first-line imaging results in selected patients, can better facilitate utilization of MIS while maintaining exceptional cure rates.David Taı ¨eb and Fre ´deric Sebag have authors contributed equally.

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