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Table 3. WHO Pathologic Classification of Differentiated
Thyroid Carcinoma (WHO, 5 Edition)
Follicular cell-derived
neoplasms
Subtypes
Malignant neoplasms—
high-grade follicular-
cell derived non-
anaplastic carcinoma
1. Poorly Differentiated Carcinoma (Turin-Criteria):
a. Solid/trabecular architecture
b. Absence of nuclear features of papillary thyroid
carcinoma
c. Tumor necrosis
d. Mitotic index ≥3/10 high power fields (HPFs)
e. And/or convoluted tumor nuclei
2. Differentiated high-grade thyroid carcinoma
a. Differentiated cytologic and architectural features
b. At least one the following two histomorphologic features
c. Mitotic count ≥5/2 mm
2
and/or tumor necrosis
Other rare neoplasms 1. Salivary gland-type carcinomas
a. Mucoepidermoid carcinoma of the thyroid
b. Secretory carcinoma of salivary gland type
2. yroid tumors of uncertain histogenesis
a. Sclerosing mucoepidermoid carcinoma with eosinophilia
b. Cribriform morular thyroid carcinoma
3. ymic tumors within the thyroid
a
Formerly classified as non-invasive and encapsulated follicular variant of papillary thyroid
carcinoma.
b
See Table 2.
c
Includes rare subtypes such as PTC with fibromatosis/fasciitis-like stroma, clear cell subtype,
spindle cell subtype, etc.
(cont'd)
