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A squamous odontogenic tumor (SOT) is an epithelial locally benign neoplasia derived from the periodontium of the jaws. It is considered a lesion of low incidence. Predominantly, it affects the mandible, although both jaw bones may be involved. Here, we discuss the malignant clinical evolution of an SOT lesion in an 80-year-old female patient. The patient exhibited an expansive triangular lesion at the inferior right quadrant. Surgery was performed and an SOT was diagnosed (2019). Two years after, the lesion grew, and the analysis of the biopsy revealed SOT malignization with pleomorphic atypical squamous cells, characteristics of a squamous cell carcinoma (2021). Massive DNA sequencing of formalin-fixed–paraffin-embedded specimens of the initial and relapsed tumors indicated pathogenic mutations in RET and POLE genes in both tumors, loss of ALK, and gain of CDKN1B and MAP2K in the relapse. In addition, the clinical, radiographic, and microscopic features of this neoplasm are discussed and compared with those already published. The case presented contributes to the better understanding of this SOT tumor entity and to indicates its malignant evolution, together with its biological behavior and its histologic, clinical, and radiographic features. Also, it aims to stress the importance of deeper genetic analyses in rare diseases to uncover mutations that help to select a personalized treatment.

Squamous odontogenic tumor (SOT) is a rare benign but locally infiltrative tumor often misdiagnosed as other entities, such as ameloblastoma and squamous cell carcinoma, due to overlapping morphological findings. We document here the clinicopathological and imaging findings of an aggressive intraosseous SOT in the posterior left region of the maxilla in a 25-year-old male patient. On intraoral examination, the tumor extended from the region of the left lateral incisor to the upper left premolar and was covered by reddish mucosa, with discrete areas of ulceration. Imaging exams revealed an osteolytic lesion causing thinning, erosion, and buccal and lingual cortical plate perforation associated with an impacted canine. Microscopically, the tumor showed a proliferation of islands of well-differentiated squamous epithelium in a variably collagenized background. The peripheral cells of the islands were flat or slightly cuboidal and did not exhibit nuclei with peripheral palisade and reverse polarization. The diagnosis of SOT was rendered. The patient underwent surgical resection and has been under clinical follow-up for approximately 12 months with no signs of recurrence. A careful morphological evaluation is essential to avoid misdiagnosis and ensure a satisfactory treatment approach.

The latest (4th) edition of the World Health Organization Classification of Head and Neck tumours has recently been published with a number of significant changes across all tumour sites. In particular, there has been a major attempt to simplify classifications and to use defining criteria which can be used globally in all situations, avoiding wherever possible the use of complex molecular techniques which may not be affordable or widely available. This review summarises the changes in Chapter 8: Odontogenic and maxillofacial bone lesions. The most significant change is the re-introduction of the classification of the odontogenic cysts, restoring this books status as the only text which classifies and defines the full range of lesions of the odontogenic tissues. The consensus group considered carefully the terminology of lesions and were concerned to ensure that the names used properly reflected the best evidence regarding the true nature of specific entities. For this reason, this new edition restores the odontogenic keratocyst and calcifying odontogenic cyst to the classification of odontogenic cysts and rejects the previous terminology (keratocystic odontogenic tumour and calcifying cystic odontogenic tumour) which were intended to suggest that they are true neoplasms. New entities which have been introduced include the sclerosing odontogenic carcinoma and primordial odontogenic tumour. In addition, some previously poorly defined lesions have been removed, including the ameloblastic fibrodentinoma, ameloblastic fibro-odontoma, which are probably developing odontomas, and the odontoameloblastoma, which is not regarded as an entity. Finally, the terminology “cemento” has been restored to cemento-ossifying fibroma and cemento-osseous dysplasias, to properly reflect that they are of odontogenic origin and are found in the tooth-bearing areas of the jaws.

The 4th edition of the World Health Organization’s Classification of Head and Neck Tumours was published in January of 2017. This article provides a summary of the changes to Chapter 4 Tumours of the oral cavity and mobile tongue and Chapter 8 Odontogenic and maxillofacial bone tumours. Odontogenic cysts which were eliminated from the 3rd 2005 edition were included in the 4th edition as well as other unique allied conditons of the jaws. Many new tumors published since 2005 have been included in the 2017 classification.

The 5th edition of the World Health Organization (WHO) Classification of Head and Neck Tumours (2022) comes out only five years after the previous edition, however it presents important updates that run in parallel with the rapid progression involving the increasingly sophisticated molecular investigation and its interpretation, some of which already have therapy-related impact. This manuscript provides an overview of the leading changes introduced in the classification of Odontogenic and Maxillofacial Bone Tumours that encompasses cysts of the jaws, odontogenic tumours, giant cell lesions and bone cysts, and bone and cartilage tumours. This is the first edition that Essential and Desirable Diagnostic Features were added for each entity, so that the most important clinical, microscopic and/or radiologic features were encapsulated and briefly highlighted. Surgical ciliated cyst was added to the group of odontogenic cysts, adenoid ameloblastoma was a newly recognized benign epithelial odontogenic tumour, and segmental odontomaxillary dysplasia was introduced in the group of fibro-osseous tumours and dysplasia. In addition, rhabdomyosarcoma with TFCP2 rearrangement, was introduced into the group of malignant jawbone tumours. The unique genetic aberrations distinguish it from other types of rhabdomyosarcomas. On the other hand, melanotic neuroectodermal tumour of infancy and osteoid osteoma were deleted from the benign bone and cartilageneous tumours, as was the hematolymphoid tumour of solitary plasmacytoma of bone. We systematically reviewed each entity in this chapter and provided important updated findings for selected topics that can further aid in the diagnostic process for challenging cases, broaden insights on the logic of the present classification, and finally, emphasize the potential that some of the molecular results may have in the near future to set new treatment approaches.

To retrospectively evaluate and classify odontogenic cysts and tumours in paediatric patients, highlighting their clinical characteristics, diagnostic challenges and management strategies. A retrospective case series was conducted using archived clinical and histopathological data of paediatric patients (≤ 18 years) diagnosed with odontogenic cysts and tumour which were collected for the past 1 year (2023–2024). The majority of odontogenic lesions in the current case series appear between the ages of 13 and 18, which is the age at which permanent dentition occurs. Three of the cases had OKC, three had ameloblastoma and one had odontoma. Conclusion : Paediatric odontogenic cysts and tumours, though rare, exhibit unique clinical and radiographic characteristics that differentiate them from adult cases. Early diagnosis and conservative treatment approaches are essential to preserve jaw development and minimize recurrence risks. Further prospective studies with long-term follow-up and genetic analysis are needed to improve the understanding and management of these lesions in paediatric patients. What is Known: • Odontogenic cysts and tumours are rare in paediatric patients and often present diagnostic challenges. • Adult-based data dominates current literature. What is New: • This study presents paediatric-specific retrospective case series highlighting unique clinical, radiological and histopathological features of lesions. • It proposes a decision-making flowchart tailored for paediatric jaw lesions.

Keratocystic odontogenic tumor (KCOT) arises as part of Gorlin syndrome (GS) or as a sporadic lesion. Gene mutations and loss of heterozygosity (LOH) of the hedgehog receptor PTCH1 plays an essential role in the pathogenesis of KCOT. However, some KCOT cases lack evidence for gene alteration of PTCH1, suggesting that other genes in the hedgehog pathway may be affected. PTCH2 and SUFU participate in the occurrence of GS-associated tumors, but their roles in KCOT development are unknown. To elucidate the roles of these genes, we enrolled 36 KCOT patients in a study to sequence their entire coding regions of PTCH1, PTCH2 and SUFU. LOH and immunohistochemical expression of these genes, as well as the downstream targets of hedgehog signaling, were examined using surgically-excised KCOT tissues. PTCH1 mutations, including four novel ones, were found in 9 hereditary KCOT patients, but not in sporadic KCOT patients. A pathogenic mutation of PTCH2 or SUFU was not found in any patients. LOH at PTCH1 and SUFU loci correlated with the presence of epithelial budding. KCOT harboring a germline mutation (Type 1) showed nuclear localization of GLI2 and frequent histological findings such as budding and epithelial islands, as well as the highest recurrence rate. KCOT with LOH but without a germline mutation (Type 2) less frequently showed these histological features, and the recurrence rate was lower. KCOT with neither germline mutation nor LOH (Type 3) consisted of two subgroups, Type 3A and 3B, which were characterized by nuclear and cytoplasmic GLI2 localization, respectively. Type 3B rarely exhibited budding and recurrence, behaving as the most amicable entity. The expression patterns of CCND1 and BCL2 tended to correlate with these subgroups. Our data indicates a significant role of PTCH1 and SUFU in the pathogenesis of KCOT, and the genotype-oriented subgroups constitute entities with different potential aggressiveness.

This study aims to characterize the histomorphology of mixed odontogenic tumors, using mathematical morphology algorithms applied to digital images. Five cases of primordial odontogenic tumor (POT), 5 cases of ameloblastic fibroma, 5 cases of developing odontoma (DO), and 5 cases of tooth germs (TG) were analyzed. Histological sections stained with Haematoxylin & Eosin were digitized and the epithelial compartments were segmented into ‘virtual cells’ to further characterize the tissue compartment architecture. A comparison of the mean area of virtual epithelial cells in the entities investigated showed that, despite data distribution between the entities being similar, statistically significant differences (p < 0.001) were found, being larger for DO and smaller for AF. Additionally, DO exhibits a broader data distribution of the area compared to the other entities. Significant differences were not found between TG and POT without subepithelial condensation. Quantitative tissue analysis showed that, in focal areas, POT more closely resembles TG than other mixed odontogenic tumors. These findings suggest that virtual cell–based morphometric analysis may provide complementary quantitative information in diagnostically challenging cases, although validation in larger datasets is required.

Odontogenic myxoma (OM) and odontogenic myxofibroma (OMF) are rare benign odontogenic tumors characterized by heterogeneous stromal composition, for which objective and reproducible pathological evaluation remains challenging. This multicenter study aimed to quantitatively assess fibrous tissue proportion (FTP) using AI-assisted digital pathology and to explore its clinicopathological relevance across odontogenic myxoma spectrum lesions. A total of 143 surgical specimens were collected from 34 institutions, and 100 cases were included after centralized pathological review. FTP was independently estimated by two board-certified oral pathologists to generate expert reference data. Whole-slide images of Masson’s trichrome–stained sections were analyzed using a multi-stage deep learning pipeline implemented within a unified digital pathology platform. Agreement between expert assessment and quantitative measurements was evaluated, and associations between FTP and clinical variables were explored. Quantitative FTP measurements showed good agreement with expert pathological evaluation and revealed substantial inter-institutional variability in pathological diagnoses. In clinicopathological analyses, higher FTP was independently associated with unilocular radiological morphology. These findings demonstrate that AI-assisted quantitative pathology provides a reproducible framework for visualizing stromal heterogeneity in odontogenic myxoma spectrum lesions and may support more consistent clinicopathological interpretation across institutions.

Adenoid ameloblastoma is a very rare benign epithelial odontogenic tumor characterized microscopically by epithelium resembling conventional ameloblastoma, with additional duct-like structures, epithelial whorls, and cribriform architecture. Dentinoid deposits, clusters of clear cells, and ghost-cell keratinization may also be present. These tumors do not harbor BRAF or KRAS mutations and their molecular basis appears distinct from conventional ameloblastoma but remains unknown. We assessed CTNNB1 (beta-catenin) exon 3 mutations in a cohort of 11 samples of adenoid ameloblastomas from 9 patients. Two of the 9 patients were female and 7 male and in 7/9 patients the tumors occurred in the maxilla. Tumors of 4 of these 9 patients harbored CTNNB1 mutations, specifically p.Ser33Cys, p.Gly34Arg, and p.Ser37Phe. Notably, for one patient 3 samples were analyzed including the primary tumour and two consecutive recurrences, and results were positive for the mutation in all three tumors. Therefore, 6/11 samples tested positive for the mutation. In the 6 mutation-positive samples, ghost cells were present in only 2/6, indicating beta-catenin mutations are not always revealed by ghost cell formation. Dentinoid matrix deposition was observed in 5/6 mutation-positive samples and clear cells in all 6 cases. None of the cases harbored either BRAF or KRAS mutations. Beta-catenin immunoexpression was assessed in the samples of 8 patients. Except for one wild-type case, all cases showed focal nuclear expression irrespective of the mutational status. Together with the absence of BRAF mutation, the detection of beta-catenin mutation in adenoid ameloblastomas supports its classification as a separate entity, and not as a subtype of ameloblastoma. The presence of this mutation may help in the diagnosis of challenging cases.