Calcitonin

Calcitonin is produced by the parafollicular (C cells) of the thyroid in humans. It is primarily used by Pathologists as a marker for medullary thyroid carcinoma, which stains positive in approximately 95% of cases. Variants of medullary carcinoma such as follicular, papillary or encapsulated subtypes may be difficult to separate from more common thyroid tumors without calcitonin staining. Paragangliomas may also show overlapping histologic features. Calcitonin will also highlight C cell hyperplasia in cases of familial medullary thyroid carcinoma.
(ref: Arch Pathol Lab Med 2008;132:359. Am J Chin Pathol 2001;115:S56).