According to the WHO definition, the histological classification of thyroid tumors is mainly divided into primary epithelial tumors, primary non-epithelial tumors and secondary tumors. The specific classification is shown in Table 4.
Table 4 WHO histologic classification of thyroid tumorsThe thyroid has two different endocrine cells with different functions. About 95% of thyroid tumors originate from the follicular epithelium of the thyroid, and the rest mostly originate from the parafollicular cells of the thyroid. Mixed follicular epithelial and parafollicular cell tumors are rare, and it is controversial whether tumor cells containing both follicular epithelial and parafollicular cell sources are a 19 separate thyroid tumor in terms of histologic origin. Thyroid lymphoma is the most common tumor of non-epithelial origin of the thyroid gland and may occur independently of the thyroid gland or as part of a systemic lymphatic system tumor. Thyroid sarcomas and secondary thyroid malignancies are less common in clinical practice.