Diagnosis:
Medullary thyroid carcinoma
• The lesion depicted is medullary thyroid carcinoma (MTC). The neoplastic cells are dispersed or, as in these photomicrographs, form loose clusters. They rarely form microfollicles or papillae.
• In the main photo, a Diff Quik-stained smear, the neoplastic cells mostly appear oval. In the inset photo of a Papanicolaou-stained smear, the tumor cells have a spindly appearance. However, they also may have plasmacytoid, polygonal, oncocytic or giant cell appearances; may demonstrate mild pleomorphism; and may be bi-or multinucleated.
• The nuclei often have a “salt-and-pepper” or “speckled” chromatin pattern on Pap-stained smears (inset photo). Small nucleoli may be seen, but are usually inconspicuous. Mitotic figures are present in 15% of cases.
• On Diff-Quik staining, red cytoplasmic granules, corresponding to neurosecretory granules containing calcitonin, may be seen. The neoplastic cells of medullary carcinoma appear positive with immunocytochemical staining for calcitonin and generally are also positive for carcinoembryonic antigen (CEA), chromogranin, synaptophysin, and thyroid transcription factor 1 (TTF-1).
• MTC generally does not stain for thyroglobulin. Although amyloid may be present in the stroma of MCC, it is often absent in aspirated specimens. When present, extracellular amyloid is positive with Congo red and crystal violet stains. Glial fibrillary acidic protein (GFAP) is an intermediate filament protein found in glial cells, such as astrocytes and ependymal cells.
• The lesion depicted is medullary thyroid carcinoma (MTC). The neoplastic cells are dispersed or, as in these photomicrographs, form loose clusters. They rarely form microfollicles or papillae. In the main photo, a Diff Quik-stained smear, the neoplastic cells mostly appear oval. In the inset photo of a Papanicolaou-stained smear, the tumor cells have a spindly appearance;however, they also may have plasmacytoid, polygonal, oncocytic or giant cell appearances; may demonstrate mild pleomorphism; and may be bi-or multinucleated. The nuclei often have a “salt-and-pepper” or “speckled” chromatin pattern on Pap-stained smears (inset photo). Small nucleoli may be seen, but are usually inconspicuous. Mitotic figures are present in 15% of cases. On DiffQuikstaining, red cytoplasmic granules, corresponding to neurosecretory granules containing calcitonin, may be seen.
