Clinically Relevant Prognostic Parameters in Differentiated Thyroid Carcinoma.

Although differentiated thyroid carcinomas typically pursue an indolent clinical course, it is important to identify the subset of tumors that are most likely to behave aggressively so that patients with these tumors are counseled and treated appropriately. Extent of disease is fundamental to the prognostication for differentiated thyroid carcinoma; however, there are additional histologic features of the tumor separate from extent of disease that have been shown to affect clinical course. This review will start with a discussion of aggressive variants of papillary thyroid carcinoma, move to the prognostic significance of vascular invasion in follicular thyroid carcinoma, and finish with a discussion of Hürthle cell carcinoma, with an emphasis on why it is not considered a subtype of follicular thyroid carcinoma in the 2017 WHO Classification of Tumors of Endocrine Organs.