False-positive findings on 6-[18F]fluor-l-3,4-dihydroxyphenylalanine PET (F-FDOPA-PET) performed for imaging of neuroendocrine tumors.

Background/aim: PET with 6-[18F]fluor-l-3,4-dihydroxyphenylalanine (F-FDOPA) has been shown to be a useful imaging tool with a high sensitivity for the visualization of neuroendocrine tumors (NETs). F-FDOPA uptake in tumors other than NETs has been suggested previously, but data on this phenomenon are limited. We therefore studied the non-physiological, false-positive uptake of F-FDOPA in a large population of patients with a NET or with a high clinical suspicion of harboring a NET.

Patients And Methods: Retrospective single-center study among adult patients in whom F-FDOPA PET scintigraphy was performed between January 2004 and December 2014. The original scan report was compared with the original pathology report corresponding with the F-FDOPA PET-positive lesion. In case this was inconsistent with the diagnosis of a NET, both the scan and the pathology slides were reassessed. Specimens of these non-NET tissues were immunohistochemically stained for AADC.

Results: 1070 F-FDOPA PET scans from 705 patients were evaluated. Focal or multiple F-FDOPA-avid lesions were described in 709 F-FDOPA PET scans (66%). Histology of these F-FDOPA PET-positive lesions was present in 508 (72%) cases. In seven cases, the histopathology was not compatible with NET but showed squamous cell carcinoma of the cervix, multiple myeloma (two cases), hepatocellular carcinoma, Schwannoma, adrenocortical carcinoma and a skeletal myxoid chondrosarcoma, with positive immunohistochemical staining for AADC in 67%.

Conclusions: Pathological uptake of F-FDOPA does not always indicate the presence of a NET. The possibility of F-FDOPA uptake by tumor types other than NETs, although rare, should be considered.