[Interpretation of the fourth edition of WHO pathological classification of the thyroid tumors in 2017]

In recent years, the incidence of thyroid carcinoma gradually increased in China. The pathology diagnosis and classification was based on WHO classification of Tumors of Endocrine Organs, the third edition which published in 2004. The fourth edition, WHO classification of Tumors of Endocrine Organs was published in July 2017. Compared with the third, some important aspects (or points) were revised: the ICD-O code of hyalinizing trabecular tumor was changed from 0 to 1; three other encapsulated follicular-patterned thyroid tumors were added; the variants of well differentiation thyroid carcinoma (including papillary carcinoma and follicular carcinoma ) which was originated from thyroid epithelial cells were updated; oncocytic cell tumors were separated from follicular tumors; the ICD-O code of ectopic thymoma was changed from 1 to 3. Refinement and standardization part of the concepts and diagnostic criterias were done which can solve practical problems in pathology diagnosis.