Incidental medullary thyroid microcarcinoma revealed by mild increase of preoperative serum calcitonin levels: therapeutic implications

To investigate whether further, diagnostic procedures should be recommended in patients with slight increase of preoperative serum basal calcitonin (bCT) levels in whom surgical treatment can be recommendable. Fourteen consecutive patients with nodular thyroid disease underwent thyroidectomy in our center for suspected medullary thyroid microcarcinoma (MTC) because their serum bCT levels were slightly higher than the upper limit of normal range. Serum bCT was measured by radioimmunoassay, normality range = 0–20 ng/L. Surgical specimens were examined by the same pathologist using histologic and immunohistochemistry techniques. An extensive search for parafollicular C-cell hyperplasia (CCH) and/or microscopic MTC foci was performed. At preoperative ultrasound, a single thyroid nodule was depicted in three patients while a multinodular goiter in 11. The bCT values ranged between 24.4 and 94.6 ng/L, median 42.2 ng/L while the pentagastrin-stimulated CT (sCT) values by pentagastrin test ranged between 61.5 and 1,262 ng/L, median 245.0 ng/L. Total thyroidectomy was performed in 13 patients, and lobectomy in the other one; central node dissection was also performed in eight cases. At histology, MTC was diagnosed in nine patients (64.3 %), showing a median maximum diameter of 6.1 mm (range, 1.5–17 mm); CCH was diagnosed in the other five patients (35.7 %). The pentagastrin stimulation test was obtained in all patients. It is worth noting that a very high increase of sCT >100 ng/mL was observed in 5/9 patients with MTC and in 2/4 patients with HCC, therefore suggesting the absence of a relationship between the entity of response to pentagastrin test with a specific pathology (MTC vs. HCC). In six patients, the MTC was the nodule on which preoperative FNAC had been performed, while in other three patients preoperative FNAC had been performed on a different nodule from the MTC. Based on our experience, in case of the pentagastrin stimulation test with sCT <100 ng/L and a single nodule, the CT assay on FNAC may be useful, subsequently lobectomy with definitive histological diagnosis is recommended. In case of the Pg test with sCT <100 ng/L and bilateral goiter, total thyroidectomy with histological diagnosis is recommended. In this way, as for the surgical procedure, total thyroidectomy is recommended in cases of bilateral goiter, while lobectomy can be offered for cases with single nodes with serum dosage of bCT in the strict follow up. In case of the pentagastrin stimulating test with sCT <100 ng/L and bilateral goiter, total thyroidectomy with histological diagnosis is recommended.