Critical appraisal of the WHO 2022 classification of thyroid cancer

Abstract

The WHO Classification of Endocrine and Neuroendocrine Tumors, Fifth Edition, is a current publication that includes relevant revisions to the nomenclature, grading, and prognostication of endocrine tumors based on pathologic characteristics and molecular profile. Additional entities such as thyroid follicular nodular disease, follicular adenoma with papillary architecture, and oncocytic adenoma of the thyroid are included in the benign follicular cell-derived category. Fifth edition WHO has refined the spectrum of papillary thyroid carcinoma (PTC) by aligning invasive encapsulated follicular variant PTCs with follicular thyroid carcinomas. Follicular cell-derived differentiated thyroid carcinomas may also have high-grade features in the absence of morphologic dedifferentiation, and hence, differentiated thyroid carcinomas with high-grade features are now recognized as a distinct morphologic spectrum. The Ki-67 proliferation index reporting is required in all medullary thyroid carcinomas for grading.