Benign odontogenic tumors: WHO classification update and clinical implications

OBJECTIVES This work aims toward reporting the most significant changes between the 3rd and 4th edition of the WHO classification of head and neck tumors (maxillary cysts included). The comparison between the last two editions of the WHO classification doesn't show only the taxonomic variations, but it also reports the most up-to-date clinical evidence concerning the diagnosis, the treatment and the prognosis of these growths. MATERIALS AND METHODS We investigated all the editions of the WHO classification of head and neck tumors published since 1971 by searching PubMed database, focusing in particular on benign odontogenic tumors. Furthermore, we selected the most significant articles concerning the most up-to-date diagnostic and therapeutic protocols for every lesion using the same search engine. In particular, we focused on lesions that were modified between the WHO classifications in years. RESULTS The WHO classification published in 2017 made 2 main adjustements: a remarkable simplification of the classification framework of the malign and benign tumors; the reintroduction of odontogenic cysts into the WHO classification of benign odontogenic and maxilla-facial tumors. Treatment protocols of the following lesions received major changes: orthokeratinized odontogenic cyst, odontogenic keratocyst, calcifying odontogenic cyst, metastasizing ameloblastoma, primordial odontogenic tumour, cemento-ossifying fibroma, familial gigantiform cementoma, cemento-osseous dysplasia and osteochondroma. DISCUSSION The WHO classification update regarding head and neck tumours (2017) caused relevant changes both from a diagnostic-therapeutic approach and from the follow-up frequency and duration. Indeed, the last WHO classification defined odontogenic tumour as a rare and benign entity (1% of tumours of oral cavity) with a local aggressive progression. For instance, the keratocyst was renamed into keratocystic odontogenic tumor in 2005 (3rd edition of WHO classification) due to its local aggressive behaviour and the high percentage of recurrences. Moreover, the treatment protocol deemed a more aggressive surgical approach. The 4th edition of the WHO classification introduced an important change to the keratosic odontogenic tumor. It wasn't only recognized as a cyst, but it was also classified in two different and distinguished variants: the orthokeratinized odontogenic cyst and the odontogenic keratocyst. Each of these two variants has a specific treatment and follow-up protocol. The ameloblastoma was classified as a benign tumor in 2005. The new classification introduced a new variant characterized clinically by a malignant behaviour; its name is metastasizing ameloblastoma. Although its rare incidence, this variant implied a more aggressive surgical approach since the beginning. CONCLUSIONS WHO classification of head and neck tumours didn't report fundamental changes only from an histo-pathological point of view, but it also described clinical aspects using therapeutic protocols for every lesion taken into account. CLINICAL SIGNIFICANCE The differences between the lastest WHO classifications of odontogenic tumors, prognosis and therapy of the most important lesions are presented in this paper in order to help oral health clinicians to treat patients following the available guidelines.