Comparison of 68Ga PET/CT to Other Imaging Studies in Medullary Thyroid Cancer: Superiority in Detecting Bone Metastases

Context: Persistent disease after surgery is common in medullary thyroid cancer (MTC), requiring lifelong radiological surveillance. Staging workup includes imaging of neck, chest, abdomen, and bones. A study integrating all sites would be ideal. Despite the established use of gallium-68 (Ga-68) positron emission tomography (PET)/CT with somatostatin analogues in most neuroendocrine tumors, its efficacy is controversial in MTC. Objective: Evaluate the efficacy of Ga-68 PET/CT in detecting MTC lesions and evaluate tumor expression of somatostatin receptors (SSTRs) associated with Ga-68 PET/CT findings. Methods: Prospective study evaluating 30 patients with MTC [group 1 (n = 16), biochemical disease; group 2 (n = 14), metastatic disease]. Patients underwent Ga-68 PET/CT, bone scan, CT and ultrasound of the neck, CT of the chest, CT/MRI of the abdomen, and MRI of the spine. Ga-68 PET/CT findings were analyzed by disease site as positive or negative and as concordant or discordant with conventional studies. Sensitivity and specificity were calculated using pathological or cytological analysis or unequivocal identification by standard imaging studies. Immunohistochemical analysis of SSTRs was compared with Ga-68 PET/CT findings. Results: In both groups, Ga-68 PET/CT was inferior to currently used imaging studies except for bone scan. In group 2, Ga-68 PET/CT sensitivities were 56%, 57%, and 9% for detecting neck lymph nodes, lung metastases, and liver metastases, respectively, and 100% for bone metastases, superior to the bone scan (44%). Expression of SSTRs, observed in 44% of tumors, was not associated with Ga-68-DOTATATE uptake. Conclusions: Ga-68 PET/CT does not provide optimal whole-body imaging as a single procedure in patients with MTC. However, it is highly sensitive in detecting bone lesions and could be a substitute for a bone scan and MRI.