Abstract
The 5th edition of the WHO Classification of Head and Neck Tumours was published online in 2022. The edition introduces new lists of oral potentially malignant diseases （OPMDs） and HPV-associated oral epithelial dysplasia, which are now classified as separate diseases from conventional oral epithelial dysplasia （OED）. In the 5th edition, the three-tiered classification system for OED is maintained, but the binary system is also mentioned. In addition, the 5th edition adds histological features that consider the proliferative potential and differentiation of cells concerning the structural and cytological characteristics seen in OED. Squamous cell carcinoma was listed at the beginning of the chapter on “Tumours of the oral cavity and mobile tongue” in the 4th edition of the WHO classification, but in the 5th edition, it is moved to the end of the chapter. Verrucous carcinoma and carcinoma cuniculatum, which have been treated as subtypes of squamous cell carcinoma, are now listed as separate items based on their characteristic clinical and pathological features, as well as pathogenesis. This report outlines the changes made to the classification of oral epithelial tumors in the 5th edition of the WHO Classification of Head and Neck Tumours.
