Long-term calcitonin after thyroidectomy for medullary thyroid cancer in MEN2A

Thyroidectomy is recommended for patients with multiple endocrine neoplasia type 2A (MEN2A). American Thyroid Association 2015 guidelines recommend follow-up of calcitonin values after thyroidectomy. The aim of this study was to determine the natural course of calcitonin levels after total thyroidectomy (TTx) in MEN2A patients. Patients with MEN2A who underwent TTx between 1993 and 2019 and had multiple postoperative calcitonin measurements were retrospectively included from our referral center. Long-term serial calcitonin measurements and clinical outcomes were correlated to the first postoperative calcitonin, histopathology and type of TTx (prophylactic versus non-prophylactic). Fifty-two patients underwent TTx after 1993 at a median age of 10 years (range 0-71). Of these, 23 (44%) had no MTC and 29 (56%) had MTC. The median follow-up time was 12 years (range 3-30). Thirty-eight patients had an 'undetectable' first postoperative calcitonin, seven 'within reference range' and seven 'above reference range'. Of the 38 patients with an 'undetectable' first postoperative calcitonin, 32 remained 'undetectable'. All 21 patients without MTC and 'undetectable' first postoperative calcitonin remained 'undetectable'. Of the 17 patients with MTC and 'undetectable' first postoperative calcitonin, 11 remained 'undetectable' and none developed structural recurrence. Twenty-two of the 25 patients undergoing prophylactic thyroidectomy had repeated 'undetectable' measurements. Persistent MTC or structural recurrence occurred in six patients; all had MTC, had a detectable first postoperative calcitonin and underwent non-prophylactic TTx. In conclusion, the long-term serial calcitonin values remain undetectable in the majority of the patients with an undetectable first postoperative calcitonin. Biochemical follow-up for patients without MTC and an undetectable first postoperative calcitonin may not be necessary.