The major changes in the 2022 World Health Organization (WHO) classification of thyroid tumors, including medullary thyroid carcinoma, and their clinical relevance were summarized by Korean and Japanese researchers in a review article published in Endocrinology and Metabolism.
This is important because the changes will have an impact on the upcoming releases of clinical guidelines, cancer staging protocols, thyroid histopathology reporting standards, and cytology reporting systems.
“Clinicians and pathologists need to be aware of new terminologies and classification schemes,” the authors stated.
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According to the new classification, neoplasms derived from follicular cells are categorized into 3 classes, which are benign tumors, low-risk neoplasms, and malignant neoplasms.
Novel terms have been introduced to the classification, such as “follicular nodular disease” and “differentiated high-grade thyroid carcinoma,” while some terms have been replaced by others. For example, “Hürthle cells” has been replaced with “oncocytic cells” and “variant” has been replaced with “subtype” to describe a subclass of tumors.
To identify high-grade follicular cell-derived carcinomas and medullary thyroid carcinoma, a histologic grading system based on mitotic count, necrosis, and/or the Ki67 index has been introduced.
The new classification also introduced new categories of thyroid tumors. These are “salivary gland-type carcinomas of the thyroid” and “thyroid tumors of uncertain histogenesis.”
The most important change concerning clinicians is the introduction of the 2-tiered grading system. This will allow them to distinguish high-grade cancers from well-differentiated follicular cell-derived carcinomas and medullary thyroid carcinoma.
“The concept of low-risk neoplasm and histology-based grading systems help guide personalized therapeutic decisions for patients at different levels of risk,” first author Chan Kwon Jung, MD, PhD, and the coauthors of the review wrote. “These changes are continuing, and new updates in the WHO classification of endocrine neoplasms are expected in the next 5 years.”
Jung CK, Bychkov A, Kakudo K. Update from the 2022 World Health Organization classification of thyroid tumors: a standardized diagnostic approach. Endocrinol Metab (Seoul). Published online October 4, 2022. doi:10.3803/EnM.2022.1553