Limited role of carbidopa-assisted 18F-FDOPA PET/CT in patients with sporadic non-functional gastroduodenal neuroendocrine neoplasms

Abstract

Objective: To evaluate ¹⁸F-fluorodihydroxyphenylalanine (¹⁸F-FDOPA) positron emission tomography/computed tomography (PET/CT) after carbidopa premedication to localize sporadic, well-differentiated, nonfunctioning gastroduodenal neuroendocrine neoplasms (NENs).

Methods: Ten patients undergoing staging carbidopa-assisted ¹⁸F-FDOPA PET/CT before endoscopic or surgical resection of gastroduodenal NENs were retrospectively selected. Preoperative imaging work up also included CT, magnetic resonance imaging (MRI), and somatostatin receptor scintigraphy (SRS) single-photon emission computed tomography/computed tomography (SPECT/CT) in ten, six, and eight patients, respectively. Histopathological diagnosis of primary NEN was the diagnostic standard of truth. Metastatic spread was defined as the presence of histologically proven nodal, visceral, and/or bone metastases.

Results: Tumors were located in the duodenal bulb in five patients, in descending duodenum in three, and in the gastric fundus in two. Three patients presented with both lymph nodes and distant metastases, and two with exclusive lymphatic spread. CT and MRI detected primary tumor in one out of ten and three out of six patients, respectively. SRS failed to detect intestinal NEN in all cases. ¹⁸F-FDOPA PET/CT detected four primary NENs (one gastric and three duodenal tumors) and was false negative in six patients. NENs missed by ¹⁸F-FDOPA PET/CT were smaller than 10 mm in two cases and measured about 30 mm in three patients. The remaining tumor was detected only on blind endoscopic biopsy. Among patients who underwent both ¹⁸F-FDOPA PET/CT and SRS, three presented discordant results for primary tumor detection (PET/CT positive/SRS negative) and five showed concordant negative studies. ¹⁸F-FDOPA PET/CT correctly identified all three patients with both nodal and visceral metastatic disease and failed to detect lymph node metastases in both N+ M0 patients.

Conclusions: ¹⁸F-FDOPA PET/CT is not sufficiently accurate for localization of primary well-differentiated nonfunctioning sporadic gastroduodenal NENs. ¹⁸F-FDOPA PET/CT's value for the assessment of visceral and lymph node metastases needs to be clarified in multicenter trials including a larger number of patients.

Keywords: 18F-FDOPA; Duodenal tumors; Gastric tumors; Neuroendocrine tumors; PET.