Objective: To evaluate the usefulness of calcitonin (CT) assay in fine needle aspiration biopsy (CT-FNAB) wash-out fluid alone or combined to cytology in the pre-surgical study of medullary thyroid carcinoma (MTC) patients with thyroid nodules and of suspicious neck MTC recurrences/metastases.

Subjects and methods: Thirthy-six ultrasound (US)-guided FNAB were performed in neck masses from 23 patients with borderline or high basal and pentagastrin (PG) stimulated serum CT. Cytology and CT-FNAB were performed on a total of 18 thyroid nodules (TN) and 3 neck lymph nodes (LN) from 12 patients examined before thyroidectomy and on 6 suspicious local recurrences (LR) and 9 LN from 9 totally thyroidectomized MTC patients. On the basis of CT-FNAB values found in 15 non-MTC lesions, CT-FNAB > 36 pg/ml was considered as indicative of MTC.

Results: All the 21 positive CT-FNAB lesions (10 TN, 6 LN and 5 LR), 13 with positive cytology, were confirmed as MTC at histology. Among the 15 negative CT-FNAB suspicious masses (8 TN, 6 LN and 1 LR) 5 displayed a benign lesion at histology. The remaining 10 cases, all with benign cytology, were not operated and no evidence of MTC has been detected at follow-up. CT-FNAB reached 100% of sensitivity and specificity for MTC, while cytology displayed 61.9% of sensitivity and 80% of specificity.

Conclusions: US-guided CT-FNAB resulted the best tool to identify primary MTC and local recurrences/node metastases in MTC operated subjects. This may have important implications in the management of MTC.