Incidental thyroid C cell hyperplasia: clinical significance and implications in practice.

Incidental C cell hyperplasia (CCH) following thyroidectomy for other indications may rarely be encountered, which may raise concerns about its clinical significance and proper management. CCH can be classified as physiological (reactive) or neoplastic. Reactive CCH has no malignant potential and can be observed in association with many other thyroid diseases (including differentiated thyroid cancer); in contrast, neoplastic CCH should be considered as a preneoplastic stage in the spectrum of C cell disease, ultimately leading to the development of medullary thyroid cancer (MTC). Neoplastic CCH is commonly observed in patients with germ-line mutations in the RET oncogene (commonly in families with a history of hereditary MTC, i.e. familial MTC or multiple endocrine neoplasia type 2 (MEN2)). CCH should be considered in patients with hypercalcitoninemia without nodular thyroidopathy. Total thyroidectomy, which is commonly performed for the majority of thyroid diseases, is an adequate treatment and achieves cure, even in patients with neoplastic CCH. There is no role for cervical lymph node dissection in patients with pure CCH. In conclusion, reactive CCH has no malignant potential, in contrast to neoplastic CCH. Total thyroidectomy achieves cure of patients with CCH.