Preoperative serum calcitonin may improve initial surgery for medullary thyroid cancer in patients with indeterminate cytology

Background: Medullary thyroid cancer (MTC) is rare, with poorer outcomes than differentiated thyroid cancer. We aimed to identify areas for improvement in the pre-operative evaluation of patients with possible MTC in a high-volume endocrine surgery unit in accordance with current practice guidelines. We hypothesised that the selective use of serum calcitonin (sCT) as a biomarker for possible MTC could guide the extent of initial surgical management. Methods: We recruited MTC patients between 2000 and 2020 from the Monash University Endocrine Surgery Unit database. Demographics, tumour characteristics, pre-operative evaluation, operative management, and outcomes were analysed. Results: Of 1454 thyroid cancer patients, 43 (3%) had MTC. Pre-operatively, 36 (84%) patients with MTC confirmed on cytology (28, 65%), elevated sCT (6, 14%) or RET mutation (2, 4%). Of these 36 patients, 31 (86%) had optimal extent of thyroidectomy and lymph node dissection (LND). Five (14%) had less than total thyroidectomy due to nerve injury. Thirty-four patients had compartmental LND. In the 12 (27%) patients with indeterminate or non-diagnostic cytology, 5 had elevated sCT and were managed as above. None of the remaining seven had LND, thus potentially suboptimal surgery. Conclusion: Our findings reflect the rarity of MTC, and the challenges of pre-operative diagnosis. The addition of sCT may improve surgical planning in patients with indeterminate cytology.