Overview of the 2022 WHO Classification of Thyroid Neoplasms

Area of Science:

• Endocrinology
• Oncology
• Pathology

Background:

• The World Health Organization (WHO) Classification of Endocrine and Neuroendocrine Tumors is a critical reference for diagnosing and understanding neoplasms.
• Previous classifications have evolved, necessitating updates to reflect advances in molecular pathology and understanding of tumor behavior.
• Thyroid neoplasms represent a diverse group of tumors with varying origins, histological features, and clinical outcomes.

Purpose of the Study:

• To summarize the key changes and updates in the 5th edition of the WHO Classification of Endocrine and Neuroendocrine Tumors specifically concerning thyroid gland tumors.
• To highlight the revised categorization of follicular cell-derived neoplasms, including benign, low-risk, and malignant entities.
• To discuss the integration of molecular classification and new entities within the updated thyroid tumor taxonomy.

Main Methods:

• Review of the 5th edition of the WHO Classification of Endocrine and Neuroendocrine Tumors.
• Analysis of the revised categories for thyroid gland tumors, focusing on cell of origin, pathology, molecular features, and biological behavior.
• Synthesis of information regarding follicular cell-derived tumors, medullary thyroid carcinomas, and rare thyroid neoplasms.

Main Results:

• The 5th edition introduces new categories for thyroid tumors, enhancing understanding of their origin, pathology, and behavior.
• Follicular cell-derived tumors are now stratified into benign, low-risk (e.g., NIFTP), and malignant categories, with refined criteria for subtypes like papillary thyroid carcinoma (PTC) and follicular thyroid carcinoma.
• New classifications address entities like thyroid follicular nodular disease (FND), oncocytic carcinoma, high-grade malignancies, and rare tumors such as salivary gland-type carcinomas and thyroblastoma.

Conclusions:

• The 5th edition WHO Classification provides a more refined and biologically relevant framework for thyroid tumors.
• Updated classifications, including molecular insights and new entities, are crucial for accurate diagnosis, prognostication, and guiding clinical management of thyroid neoplasms.
• Emphasis on detailed subtyping and the use of biomarkers is recommended for improved diagnostic precision and prognostic information.