Imaging medullary thyroid cancer patients with detectable serum markers: state of the art and future perspectives

Purpose: Medullary thyroid carcinoma (MTC) originates from thyroid parafollicular C-cells and represents <5% of all thyroid cancers. Serum Calcitonin (CTn) is considered the most sensitive marker of persistent or recurrent disease and is measured in association to CEA. According to the American Thyroid Association (ATA) guidelines, following initial surgery when CTn level remains below 150 pg/mL, follow-up may rely on repeated serum marker determinations and on neck ultrasonography (US). When CTn level exceeds 150 pg/ml, additional imaging is required. In this review, we provide an overview of available imaging tools to monitor MTC course and propose an effective imaging strategy for MTC patients according to their clinical situation. Methods: A literature search focusing on available imaging tools to monitor MTC provided the currently available information for this review. Recent evidence-based reports and reviews were considered as priority over older evidence. Results: For MTC patients with detectable CTn levels and disease recurrence, PET/CT imaging with 18F-DOPA or 68Ga-DOTA-peptides present the best sensitivity for lesion detection. 18F FDG PET/CT represents a prognostic tool and is useful in case of aggressive disease. Neck ultrasound, chest CT scan and MRI of the liver and of the axial skeleton represent complementary techniques. Beyond the diagnostic accuracy, the clinical impact of imaging is variable according to different disease settings and tumor marker levels. Finally, other applications of imaging such as response to focal and systemic treatments and new promising PET tracers should be further investigated. Conclusion: The role of imaging in MTC patients improved, especially with the use of 18F-DOPA PET/CT that provides high quality diagnostic images. However, the impact on therapeutic management should be further evaluated in the different disease settings and in proper prospective trials.