[18F]F-DOPA and [18F]F-FDG-PET/CT for staging advanced medullary thyroid cancer

There is no consensus on functional imaging modalities for lesion assessment in medullary thyroid carcinoma. The aim of this single-center retrospective study was to analyze the performance of [18F]F-DOPA-PET/CT, [18F]F-FDG-PET/CT and morphologic imaging in a cohort of patients with medullary thyroid carcinoma and extrathyroidal lesions.

Forty-three patients (10 women and 33 men; median age, 62.8years), including 28 with RET mutation (germline: n=13, somatic: n=15), all with extrathyroidal morphological lesions, underwent conventional imaging, plus [18F]F-DOPA-PET/CT with early and late acquisitions (n=40), [18F]F-FDG-PET/CT (n=29) or both (n=26), for initial staging or follow-up. PET/CT scans were analyzed visually and semi-quantitatively (SUV_max of the hottest lesion). The gold standard was based on histology and imaging follow-up.

According to the gold standard, a median 2 extrathyroidal regions were involved per patient. Per-patient sensitivity was 95.0% (38/40) for [18F]F-DOPA-PET/CT, 93.1% (27/29) for [18F]F-FDG-PET/CT, and 76.9% (30/39) for morphologic imaging. [18F]F-DOPA-PET/CT identified more hepatic and osteomedullary involvement than did [18F]F-FDG-PET/CT. The combination of both PET modalities detected at least 1 additional metastatic site in 10/26 patients (38.5%). [18F]F-DOPA SUV_max was significantly higher on early than late acquisitions (P=0.0001) and correlated positively with blood calcitonin (P=0.0069). [18F]F-FDG SUV_max correlated with shorter calcitonin doubling time (P=0.0203). SUV_max and RET status did not correlate.

Our results provide insight into the complementary role of [18F]F-DOPA and [18F]F-FDG-PET/CT in a high-risk population with morphologically proven metastatic disease.