Metastatic Medullary Thyroid Cancer: The Role of 68Gallium-DOTA-Somatostatin Analogue PET/CT and Peptide Receptor Radionuclide Therapy.

Context Metastatic medullary thyroid cancer (MTC) is a rare malignancy with minimal treatment options. Many, but not all, MTCs express somatostatin receptors. Objective Our aim was to explore the role of 68Ga-DOTA-somatostatin analogue (SSA) PET/CT in patients with metastatic MTC, and to determine their eligibility for peptide receptor radionuclide therapy (PRRT). Methods We retrospectively identified patients with metastatic MTC who had 68Ga-DOTA-SSA PET/CT at five centers. We collected characteristics on contrast-enhanced CT, 68Ga-DOTA-SSA and 18F-FDG PET/CT. The efficacy of PRRT was explored in a subgroup of patients. Kaplan-Meier analysis was used to estimate time to treatment failure (TTF) and overall survival (OS). Results Seventy-one patients were included (10 local recurrence, 61 distant disease). Of the patients with distant disease, 16 (26%) had ≥50% of disease sites with tracer avidity greater than background liver, including 10 (10/61, 16%) with >90%. In 19 patients with contemporaneous contrast-enhanced CT, no disease regions were independently identified on 68Ga-DOTA-SSA PET/CT. Thirty-five patients had an 18F-FDG PET/CT, with 18F-FDG positive/ 68Ga-DOTA-SSA negative metastases identified in 15 (43%). Twenty-one patients had PRRT with a median TTF of 14 months (95%CI 8-25) and a median OS of 63 months (95%CI 21-not reached). Of the entire cohort, the median OS was 323 months (95%CI 152-not reached). Predictors of poorer overall survival included a short calcitonin doubling-time (≤24 months), strong 18F-FDG avidity and age ≥60 years. Conclusions The prevalence of high tumour avidity on 68Ga-DOTA-SSA PET/CT is low in the setting of metastatic MTC; nevertheless, PRRT may still be a viable treatment option in select patients.