Review Article

Update on Anaplastic Thyroid Carcinoma: Morphological, Molecular, and Genetic Features of the Most Aggressive Thyroid Cancer

Table 2

Differential diagnoses of squamoid category.

Thyroid lesions simulating a squamoid patternDifferential features

Pure squamous cells carcinoma(i) Entirely composed of squamous cells;
(ii) no evidence of another type of thyroid carcinoma in close proximity.

Primary head and neck squamous cell carcinoma(i) Presence of in situ component in head and neck structures;
(ii) features of “ab extrinseco” involvement of thyroid parenchyma;
(iii) PAX8 is consistently negative.

Metastatic squamous cell carcinoma of the lung(i) Presence of a lung nodule clinically detected;
(ii) PAX8 is consistently negative.

Diffuse sclerosing variant of papillary thyroid carcinoma(i) Abundant psammoma bodies;
(ii) neoplastic cells retain nuclear features of PTC;
(iii) immunoreactivity for thyroglobulin.

Mucoepidermoid carcinoma(i) Combination of squamoid and mucinous components;
(ii) thought to represent papillary carcinoma with extreme degree of squamous and mucinous metaplasia;
(iii) low grade thyroid neoplasm.

Sclerosing mucoepidermoid carcinoma with eosinophilia(i) Fibrohyaline stroma;
(ii) striking infiltration of eosinophils;
(iii) mucin secretion is often present;
(iv) typically arising in Hashimoto thyroiditis (thought to derive from metaplastic squamous nests associated with inflammatory infiltrate).

CASTLE
(carcinoma with thymus-like elements)
(i) Lymphoepithelioma-like carcinoma with foci of squamous differentiation;
(ii) pushing margins;
(iii) immunoreactivity for CD5, bcl-2, high molecular weight keratin, mcl-1 (thought to be ectopic thymic carcinoma arising from remnants of the branchial pouch);
(iv) usually indolent behavior with tendency to late recurrences.