Educational Case: Endocrine Neoplasm: Medullary Thyroid Carcinoma

Abstract

Medullary thyroid cancer is a rare neuroendocrine tumor that arises the neural crest-derived parafollicular C cells and accounts for approximately 5% to 10% of thyroid cancers worldwide. These tumor can occur sporadically or as part of hereditary tumor syndromes, such as multiple endocrine neoplasia 2 and familial medullary thyroid cancer. The most common clinical presentation is a solitary thyroid nodule. The genetic defect in these disorders involves the RET proto-oncogene which is important for diagnosis of medullary thyroid cancer (including screening for hereditary medullary thyroid cancer) and for treatment guidance. This review summarizes the molecular basis and clinicopathologic features of medullary thyroid carcinoma.

Keywords: clinical features; cytologic diagnosis; endocrine neoplasms; medullary thyroid carcinoma; molecular basis; organ system pathology; pathologic features; pathology competencies.

Figure 1.

A, Smears show singly dispersed plasmacytoid (eccentric nuclei) cells of variable sizes, abundant amphophilic cytoplasm, granular chromatin, and inconspicuous nucleoli (PAP-stained, high power ×60 magnification). B, Smear shows a loosely cohesive cluster of neoplastic cells with occasional nuclear enlargement (arrows; PAP-stained, high power ×60 magnification).

Figure 2.

Immunohistochemical stain, performed on the cellblock, shows that the neoplastic cells are positive for calcitonin (cytoplasmic and granular staining; high power ×60 magnification).

Figure 3.

Section of the thyroid nodule showing nests of round and spindle cells outlined by fibrous tissue. The cells display granular cytoplasm and round nuclei with “salt and pepper” chromatin. (Hematoxylin and eosin stained slide, high power ×40 magnification).