Diagnosis and pathologic characteristics of medullary thyroid carcinoma-review of current guidelines

Abstract

Background: Medullary thyroid carcinoma (mtc) is a rare malignancy of the thyroid gland, and raising awareness of the recommended diagnostic workup and pathologic characteristics of this malignancy is therefore important.

Methods: We reviewed the current clinical practice guidelines and recent literature on mtc, and here, we summarize the recommendations for its diagnosis and workup. We also provide an overview of the pathology of mtc.

Results: A neuroendocrine tumour, mtc arises from parafollicular cells ("C cells"), which secrete calcitonin. As part of the multiple endocrine neoplasia (men) type 2 syndromes, mtc can occur sporadically or in a hereditary form. This usually poorly delineated and infiltrative tumour is composed of solid nests of discohesive cells within a fibrous stroma that might also contain amyloid. Suspicious nodules on thyroid ultrasonography should be assessed with fine-needle aspiration (fna). If a diagnosis of mtc is made on fna, patients require baseline measurements of serum calcitonin and carcinoembryonic antigen. Calcitonin levels greater than 500 pg/mL or clinical suspicion for metastatic disease dictate the need for further imaging studies. All patients should undergo dna analysis for RET mutations to diagnose men type 2 syndromes, and if positive, they should be assessed for possible pheochromocytoma and hyperparathyroidism.

Summary: Although the initial diagnosis of a suspicious thyroid nodule is the same for differentiated thyroid carcinoma and mtc, the remainder of the workup and diagnosis for mtc is distinct.

Keywords: Medullary thyroid carcinoma; RET; amyloid; calcitonin; carcinoembryonic antigen; diagnosis; hyperparathyroidism; men2; pheochromocytoma.

FIGURE 1

Pathology of medullary thyroid carcinoma. This usually poorly delineated and infiltrative tumour is composed of solid nests of discohesive cells within a fibrous stroma that might also contain amyloid. (a) The amyloid can be recognized by its intense staining with Congo red. (b) It also exhibits apple green birefringence with polarized light (not shown). (c) Tumour cells stain for calcitonin as well as for chromogranin A and carcinoembryonic antigen (not shown). The diagnosis can be missed when a medullary thyroid carcinoma (d) has a follicular architecture, (e) pseudopapillary patterns, or (f) is oncocytic, and they can be misclassified as follicular cell–derived lesions.