SAT555 Utility of 18F-DOPA PET/CT in the Diagnosis of Medullary Thyroid Cancer in a Patient with Multiple Endocrine Neoplasia Type 2B
Authors: Varghese Diana Grace , Akshintala Srivandana , Jha Abhishek , Gubbi Sriram , Reno Annieka , Klubo-Gwiezdzinska Joanna , Pacak Karel , Glod John , Del Rivero Jaydira 
Published: October 2023

Abstract
Disclosure: D.G. Varghese: None. S. Akshintala: None. A. Jha: None. S. Gubbi: None. A. Reno: None. J. Klubo-Gwiezdzinska: None. K. Pacak: None. J. Glod: None. J. Del Rivero: None.
Background: MEN2B is a cancer predisposition syndrome caused by an activating mutation in the RET proto-oncogene. It is characterized by medullary thyroid cancer (MTC), pheochromocytoma (PHEO), and extra endocrine features. U/S, CT, MRI and 18F-fluorodeoxyglucose (18F-FDG), 18F-fluorodihyroxyphenylalanine (18F-FDOPA), 68Ga-DOTA-(0)-Tyr(3)-octreotate (68Ga-DOTATATE) PET/CT scans have been used for the diagnosis and follow up of MTC. However, there is increasing evidence of 18F-FDOPA PET as more specific imaging modality in the diagnosis of MTC since L-type amino acid transporters have shown to be present in MTC cells.Clinical Case: 26-year-old female presented with HTN at the age of 17. The patient developed episodes of nausea/vomiting, intermittent headaches with systolic BP in the 190’s. Further work-up revealed bilateral adrenal nodules with elevated plasma metanephrines. The patient underwent left adrenalectomy and a year later, right adrenal nodule resection confirming PHEO. On follow up, calcitonin was elevated, and the patient underwent a total thyroidectomy with bilateral central lymph node dissection. At age 19 she was diagnosed with MEN2B (RET mutation, p.Met918Thr). With rising calcitonin, she was referred to our institution for further evaluation. Her serum calcitonin was 31986(&lt;7.6 pg/ml), CEA 631 (0.8-3.4 ng/ml), fractionated plasma normetanephrine 565 (18-112 pg/ml), and metanephrine 304 (12-61 pg/mL). MRI of the abdomen showed enlarging adrenal masses. 18F-FDG PET/CT scan showed a focus of uptake (SUVmax of 8.5) in posterior right thyroid bed, uptake in the liver (SUVmax of 7.5) and uptake in the right adrenal gland and left adrenal bed; 68Ga-DOTATATE PET/CT scan showed a faint uptake in the right thyroid lobe (SUVmax of 2.7) and an 18F-FDOPA PET/CT scan showed intense uptake in both lobe of the thyroid, multiple lesions in the liver and suspicious focus in the right adrenal bed. The patient underwent bilateral adrenalectomy for recurrent PHEO and her plasma metanephrines normalized. Conclusion: This case adds to the mounting evidence in the usage of 18F-FDOPA PET/CT scan as a useful imaging modality for MTC especially in the setting of MEN2B syndrome. A head-to-head comparison in 18 patients, both per patient and per lesion sensitivity by 18F-FDOPA PET/CT (72%, 85%) was found to be statistically superior compared to 68Ga-DOTATATE PET/CT (33%, 20%), and 18F-FDG PET/CT (17%, 28%). A meta-analysis conducted in MTC consisting of 306 patients from 14 studies, 18F-FDOPA compared to 18F-FDG and 68Ga-DOTATATE showed the highest surface under the cumulative ranking curve (SUCRA) value in both patient and lesion-based analyses irrespective of serum calcitonin/CEA values or calcitonin doubling time. The potential for use of 18F-FDOPA as a diagnostic agent and the potential to provide insight into possible therapeutic targets are unknown and should be further studied.
Presentation Date: Saturday, June 17, 2023