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

Abstract

This work was performed to evaluate the performance of 18F- fluorodihydroxyphenylalanine (18F-FDOPA) PET/CT in detecting primary neuroendocrine tumors (NETs) occult on morphologic and functional imaging, in relation to tumor origin and differentiation. Methods: A retrospective study of NET patients who were investigated with 18F-FDOPA PET/CT imaging in 2 academic endocrine tumor centers was conducted. Only patients with negative conventional and somatostatin receptor scintigraphy (SRS) results were studied. Results: 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 duodenumG2 lesion, 7 ileumG2 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. Conclusion: 18F-FDOPA PET appears to be a sensitive functional imaging tool for the detection of primary NETs occult on SRS, especially tumors with a well-differentiated pattern and serotonin secretion. © 2014 by the Society of Nuclear Medicine and Molecular Imaging, Inc.