Epiglottic Squamous Cell Carcinoma Showing Unexpected 18F-FDOPA Uptake on PET/CT Investigation

Molecular imaging of endocrine neoplasms with emphasis on 18F-DOPA PET: a practical approach for well-tailored imaging protocols

6-[18F]-L-fluoro-L-3, 4-dihydroxyphenylalanine (¹⁸F-DOPA) PET/CT can be a useful tool for the detection of different neuroendocrine tumors (NETs). The main determinants of ¹⁸F-DOPA uptake and retention by NETs are related to expression of LAT1/LAT2 transporters, expression and activity of AADC and biochemical phenotype, all being intimately inter-connected to their embryological origin. In order to improve sensitivity of ¹⁸F-DOPA PET, it is of main importance to perform indivisualized imaging protocols across primaries. This review provides a practical approach for performing well-tailored imaging protocols and describes the clinical value of the recommended radiopharmaceuticals.

Variants and Pitfalls of PET/CT in Neuroendocrine Tumors

Management of patients with neuroendocrine neoplasms (NEN) is complex and warrants referral of these patients to high volume centers with appropriate expertise to ensure favorable outcomes. PET/CT becomes increasingly important in every step of their management and outcome. The choice of radiopharmaceutical heavily depends on tumor origin, which is intimately interconnected to embryology, grade and clinical presentation (eg, diagnostic vs theranostic settings). The aim of this review is to describe the role of SSTR, ¹⁸F-FDOPA, and ¹⁸F-FDG-PET imaging in the evaluation of NEN patients. There is emphasis on the main variants, caveats, and pitfalls that can be observed within these modalities. Nuclear physicians must be equipped with the skills to handle potential variants, caveats, and pitfalls that are commonly encountered in NEN imaging, and they should understand the expected imaging features that are encountered across various types of NENs.

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

BACKGROUND/AIM

PET with 6-[18F]fluor-l-3,4-dihydroxyphenylalanine (¹⁸F-FDOPA) has been shown to be a useful imaging tool with a high sensitivity for the visualization of neuroendocrine tumors (NETs). ¹⁸F-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 ¹⁸F-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 ¹⁸F-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 ¹⁸F-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 ¹⁸F-FDOPA PET scans from 705 patients were evaluated. Focal or multiple ¹⁸F-FDOPA-avid lesions were described in 709 ¹⁸F-FDOPA PET scans (66%). Histology of these ¹⁸F-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 ¹⁸F-FDOPA does not always indicate the presence of a NET. The possibility of ¹⁸F-FDOPA uptake by tumor types other than NETs, although rare, should be considered.