Poorly Differentiated Thyroid Carcinoma

Abstract

Poorly differentiated thyroid carcinoma (PDTC) was first proposed as a distinct subtype of thyroid malignancy by Carcangiu et al. These authors reinterpreted the original observation made in 1907 by Langhans, who described a locally aggressive tumor with a peculiar architecture: tumor cells arranged in large, round to oval formations, the so-called “insulae.” Currently, there are 2 recognized subtypes of PDTC - insular and non-insular. PDTC is a rare malignancy, accounting for 4–7% of all thyroid cancers. It has an aggressive clinical behavior intermediate between that of the well differentiated thyroid carcinomas (papillary carcinoma, follicular carcinoma, and Hurthle cell carcinoma) and undifferentiated (anaplastic) thyroid carcinoma. PDTCs often present at an advanced stage, have a propensity for local recurrence, and tend to metastasize to regional lymph nodes, lung, and bones. The mean 5-year survival of patients with PDTC is approximately 50%. Well differentiated thyroid carcinomas with a focal (10% or greater) PDTC component follow a more aggressive clinical course than standard well differentiated carcinomas of the thyroid.