18F-Fluorodihydroxyphenylalanine PET/CT in patients with neuroendocrine tumors of unknown origin: relation to tumour origin and differentiation

The role of PET tracers in managing Neuroendocrine tumours (NETs) is evolving. There are a number of new tracers that are being evaluated to help with the diagnosis and management of NETS. This study aimed to evaluate the performance of 18F-fluorodihydroxyphenylalanine (18F-FDOPA) PET/CT in detecting primary neuroendocrine tumors (NETs) that cannot be identified using standard cross sectional or functional imaging. This was a retrospective study performed at 2 nuclear medicine centres. Patients were investigated with 18F-FDOPA PET/CT imaging only if the primary tumour was not identified using conventional imaging and somatostatin receptor scintigraphy (SRS).

Twenty-seven patients were evaluated with 18F-FDOPA PET/CT, 23 at their initial staging and 4 during their follow-up. The primary occult NET was localized by 18F-FDOPA PET/CT in 12 patients (overall sensitivity, 44%; 52% in patients evaluated at initial diagnosis), leading to tumor resection in all cases. The primary tumors were distributed and graded as follows: 1 duodenum G2 lesion, 7 ileum G2 lesions, 2 terminal ileum G1 lesions, 1 pancreas G2 lesion, and 1 gallbladder G3 lesion. Patients with positive 18F-FDOPA PET/CT results had higher values of serum chromogranin A (100% vs. 20%, P = 0.0003), serotonin, or urinary 5-hydroxyindolacetic acid (83% vs. 20%, P = 0.003). Two false-negative results were related to poorly-differentiated duodenal and prostatic NETs (G3). 18F-FDOPA PET/CT showed more metastatic anatomic regions than SRS in 17 patients.

In summary, 18F-FDOPA PET appears to be a sensitive functional imaging tool for the detection of primary NETs which have not been identified using standard cross sectional imaging or somatostatin receptor scintigraphy.

Source: Journal of Nuclear Medicine