ESA-SRB-AOTA 2019

Detection of Metastatic Sporadic Medullary Thyroid Carcinoma using PET/CT with Radiolabelled Gastrin Analogue (#174)

Rinky Giri 1 , Chris J Yates 1 2 , Mohammed Haskali 3 , Rod J Hicks 2 3
  1. Department of Endocrinology and Diabetes, Western Health, St Albans, Victoria, Australia
  2. Department of Medicine, University of Melbourne, Melbourne, Victoria, Australia
  3. Cancer Imaging, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia

Medullary thyroid carcinoma(MTC) accounts for 2-8% of thyroid carcinoma1. The production of calcitonin and carcinoembryonic antigen(CEA) are characteristic features of MTC1,2. Conventional radiographic modalities for detecting metastatic MTC have been Computerised Tomography(CT), Magnetic Resonance Imaging, 18-fluoro-2-deoxyglucose positron-emission-tomography(FDG-PET), single-photon-emission-computed-tomography and somatostatin-receptor scintigraphy3,4.

We report a case of a 36-year-old female with sporadic MTC found to have a pericardial metastatic lesion on PET/CT using gallium-labelled gastrin analogue. She presented at 29 weeks’ gestation with left sided neck mass with no evidence of thyroid dysfunction, pheochromocytoma or hypercalcemia. Fine needle aspirate was suspicious for MTC. Initial calcitonin level was 191pmol/L(reference-range <5) and CEA was 92pmol/L (reference-range <3.4). She underwent a total thyroidectomy and lymph node dissection. Histopathology demonstrated a 40-mm MTC without regional nodal involvement. Gene testing for RET Proto-oncogene was negative. Baseline staging with CT Chest/Abdomen/Pelvis showed no evidence of lymphadenopathy or metastasis. Nadir of calcitonin and CEA three months post thyroidectomy was 21.73pmol/L and 8.9pmol/L respectively. 20 months post thyroidectomy marked elevation was noted in calcitonin to 104pmol/L and CEA to 21pmol/L with no evidence of recurrence on thyroid ultrasound. Repeat staging CT Chest/Abdomen/Pelvis found no local recurrence and a pericardial nodule 11X9mm. Further staging with gallium-68 labelled with minigastrin analogue(CPO4) PET/CT showed positive tracer uptake in this pericardial node. Patient underwent robotic-assisted excision of this internal mammary lymph node. Histology was consistent with metastatic MTC.  

Cholecystokinin-2/gastrin(CCK-2) receptor overexpression is found in over 90% of MTC5,6,7. The new gastrin analogue CPO4 has shown stability and affinity to CCK-2 receptor in vitro and safety in vivo7. CPO4-labelled analogues have demonstrated to visualize all active disease sites in MTC compared to other modalities8. Hence CCK-2/gastrin receptor imaging proves to be a valid and efficient diagnostic method in staging and follow up of patients with MTC facilitating early and accurate localization of the disease5,6,7,8.

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