# 68Ga-DOTATATE PET/CT in the Initial Staging of Well-Differentiated Gastroenteropancreatic and Non-Gastroenteropancreatic Neuroendocrine Tumors: Results of a Prospective Registry

## TL;DR

A study shows that adding SSTR-PET imaging to standard scans improves staging accuracy for neuroendocrine tumors, especially for those with gastroenteropancreatic tumors.

## Contribution

This is the first large prospective study demonstrating the clinical impact of SSTR-PET in initial staging of well-differentiated neuroendocrine tumors.

## Key findings

- SSTR-PET upstaged 21.1% of gastroenteropancreatic NET patients, often revealing extrahepatic metastases.
- SSTR-PET detected liver-only metastases in 36.8% of patients previously thought to have only liver disease.
- Stage migration due to SSTR-PET led to moderate to high impact on treatment plans in over half of upstaged patients.

## Abstract

The disease extent of newly diagnosed well-differentiated neuroendocrine tumors determines patient management. Staging is routinely performed using anatomical imaging (CT and/or MRI). The purpose of the current prospective study was to determine the impact of adding the somatostatin receptor (SSTR)-PET on disease stage and whether stage migration following PET may impact patient management. We confirmed upstaging following SSTR-PET in one in five patients, more frequently with gastroenteropancreatic neuroendocrine tumors than other histologies. This may result in a moderate to high impact to the therapy plan in more than half of the upstaged patients.

Background and Objectives: At diagnosis, the initial staging of well-differentiated neuroendocrine tumors (WD NETs) aids in treatment planning. The somatostatin receptor (SSTR)-PET has been recommended for staging of WD NETs although limited data are available on its impact on non-gastroeneteropancreatic (GEP) NETs. The main purpose of this study was to compare the stage migration after the addition of SSTR-PET to the workup of patients at the initial staging of GEP NETs to those with non-GEP NETs, and its potential impact on patient management. Methods: This prospective study included patients with WD NETs at initial staging. Demographic data, results of conventional and SSTR-PET staging, and SUVmax were recorded. Three panels of experts assessed the potential impact of SSTR-PET to management. Results: There were 482 patients, including 376 with gastroenteropancreatic (GEP) NETs and 106 non-GEP NETs with a median SUVmax of 34.7 [Q1, Q3: 22.8, 59.1]) and 19.0 [Q1, Q3: 7.9, 39.8]), respectively; p < 0.001. The discordant M-stage was recorded in 111/473 patients (23.5%). PET suggested a higher stage in 78/369 GEP NETs (21.1%), including the detection of extrahepatic metastatic disease in 42/114 (36.8%) patients with liver metastases only on CI. For non-GEP NETs, PET suggested a higher stage in 10/104 (9.6%) and CI suggested a higher stage in 15/104 (14.4%), with CI detecting liver metastases more frequently. The potential impact to management for patients with discordant M-stage was scored as moderate to high between 57/101 (56.4%) and 79/101 (78.2%) of patients. Conclusions: One in five patients are upstaged following SSTR-PET, more frequently with GEP NETs than others. SSTR-PET identifies extrahepatic metastatic disease in >1/3 of patients with presumed liver-only metastases on CI. Stage migration following SSTR-PET may result in frequent moderate or significant management change.