Table 1.

Clinical overview of follicular thyroid cell-derived carcinomas

Tumor type	Prevalence (% of thyroid carcinomas)	Characteristics	Subtypes
papillary thyroid carcinoma (PTC)	80–85	Well differentiated, with papillary architecture and characteristic nuclear features, such as enlargement, oval shape, elongation, overlapping and clearing, inclusions and grooves. Propensity for lymphatic metastasis	conventional PTC (CPTC), follicular-variant PTC (FVPTC), tall-cell PTC (TCPTC), a few rare variants
follicular thyroid carcinoma (FTC)	10–15	Well differentiated, hypercellular, microfollicular patterns, lacking nuclear features of PTC. Propensity for metastasis via the blood stream	Hurthle cell thyroid carcinoma
poorly differentiated thyroid carcinoma (PDTC)	5–10	Poorly differentiated, often overlapping with PTC and FTC. Intermediate aggressiveness between differentiated and undifferentiated thyroid carcinomas
anaplastic thyroid carcinoma (ATC)	2–3	Undifferentiated, admixture of spindle, pleomorphic giant and epithelioid cells, extremely invasive and metastatic, highly lethal, may occur de novo or derive from PTC, FTC or PDTC

(modified from Ref. 75.)