Role of FNA cytology and immunochemistry in the diagnosis and management of medullary thyroid carcinoma: Report of six cases and review of the literature

Medullary thyroid carcinoma (MTC) is a rare neuroendocrine thyroid malignancy. This study retrospectively reviewed 10 fine-needle aspiration samples from six MTC patients. Aspirated specimens were from thyroid (3), cervical lymph nodes (5), left lung (1), and anterior chest wall (1). Cytomorphology consisted predominantly of plasmacytoid cells (3 cases), spindle cells (2 cases), and epithelioid cells (1 case). However, all specimens had a mixture of other cell types and "salt and pepper" chromatin. Only one specimen showed Congo-red-positive amyloid. Calcitonin was expressed in 7/7 specimens. Four patients underwent surgical excision and MTC was confirmed in all four. Follow-up studies included serum calcitonin (3/6 cases) and imaging (2/6 cases). One patient had MTC associated with multiple endocrine neoplasia IIA syndrome and one had familial MTC with a history of MTC in mother. In conclusion, the cytomorphology of MTC is typical and calcitonin immunostain is a reliable method for confirming primary or metastatic MTC. Early cytological diagnosis of MTC positively impacted patient management. Follow-up with serum calcitonin and imaging is helpful in the early detection of recurrences.