First insights for targeted therapies in odontogenic myxoma

Diode laser on excision of giant peripheral odontogenic myxoma: a rare case report and literature review

It was to report a rare case of peripheral odontogenic myxoma removed with high-power diode laser and to do an extensive review of studies of odontogenic cysts and tumors treated with high-power laser (HPL). This is a rare case of a 63-year-old male patient with a peripheral odontogenic myxoma measuring approximately 10 cm in the attached gingiva region of tooth 16 removed with a high-power diode laser (808 nm, 3 W, in continuous mode, under constant suction, with 400-µm optical fiber). A literature review was also carried out looking for articles that involved the use of HPL in the treatment of odontogenic cysts and tumors, without restriction of year or language. In the present case, there was no need for suturing, no postoperative discomfort, and minimal bleeding during the procedure. In a 12-month follow-up period, there were no signs of recurrence. Only two cases of intra-osseous odontogenic myxomas treated with HPL and 10 cases involving other odontogenic cysts and tumors were found. All studies showing HPL to be effective in treating these lesions. Despite the different types of lasers used and different parameters, it is observed that lasers are effective in the treatment of odontogenic lesions.

The molecular basis of odontogenic cysts and tumours

The advances in molecular technologies have allowed a better understanding of the molecular basis of odontogenic cysts and tumours. PTCH1 mutations have been reported in a high proportion of odontogenic keratocyst. BRAF p.V600E are recurrent in ameloblastoma and KRAS p.G12V/R in adenomatoid odontogenic tumour, dysregulating the MAPK/ERK pathway. Notably, BRAF p.V600E is also detected in ameloblastic carcinoma, but at a lower frequency than in its benign counterpart ameloblastoma. Recently, adenoid ameloblastoma has been shown to be BRAF wild-type and to harbour CTNNB1 (β-catenin gene) mutations, further suggesting that it is not an ameloblastoma subtype. CTNNB1 mutations also occur in other ghost-cell-containing tumours, including calcifying odontogenic cysts, dentinogenic ghost cell tumours and odontogenic carcinoma with dentinoid, but the link between CTNNB1 mutations and ghost cell formation in these lesions remains unclear. Regarding mixed tumours, BRAF p.V600E has been reported in a subset of ameloblastic fibromas, ameloblastic-fibrodentinomas and fibro-odontomas, in addition to ameloblastic fibrosarcoma. Such mutation-positivity in a subset of samples can be helpful in differentiating some of these lesions from odontoma, which is BRAF-wild-type. Recently, FOS rearrangements have been reported in cementoblastoma, supporting its relationship with osteoblastoma. Collectively, the identification of recurrent mutations in these aforementioned lesions has helped to clarify their molecular basis and to better understand the interrelationships between some tumours, but none of these genetic abnormalities is diagnostic. Since the functional effect of pathogenic mutations is context and tissue-dependent, a clear role for the reported mutations in odontogenic cysts and tumours in their pathogenesis remains to be elucidated.

Mandibular Radiolucencies: A Differential Diagnosis of a Rare Tumor

The diagnosis and treatment of maxillofacial cystic lesions requires careful evaluation and correlation of the clinical presentation and radiological studies. The Pindborg tumor, also known as the calcifying epithelial odontogenic tumor, is a locally invasive benign neoplasm, with only around 300 cases being published to date. This study presents a new case of this already uncommon neoplasm, not associated with an impacted tooth, and describes the clinicopathological features of this rare entity, along with a review of other reported cases. Despite surgery having been recognized as the treatment of choice for the Pindborg tumor, no firm consensus exists concerning the extension of surgical resection.

Update from the 5th Edition of the World Health Organization Classification of Head and Neck Tumors: Odontogenic and Maxillofacial Bone Tumours

The 5^th 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.

Angiogenesis in patient-derived xenografts of odontogenic myxoma

Previously, by employing 3D organotypic tissue culture and patient-derived xenograft (PDX) model, oral myxoma response to a MAPK/MEK inhibitor was observed. Gross examination of the tumour fragments obtained after 55 days of PDX grafting revealed increased capsule vascularization. Microscopic analyses showed blood capillaries intermixed with myxoma cells, but the origin of these capillaries, from mice or humans, was not established. This study aimed to investigate whether the endothelial cells observed in the myxoma PDX model are derived from the mouse or from the primary human tumour. Immunohistochemistry was performed on five tumour fragments from the PDX of myxoma after 55 days of implantation in mice. Immunopositivity for antibodies against human (HLA-ABC) and mouse (H2 Db/H2-D1) major histocompatibility complex class I (MHCI) was assessed in the endothelial cells. The endothelial cells in the PDX fragments revealed a membrane staining for the human MHCI protein in the PDX tumour and adjacent connective tissue capsule, indicating that capillaries were derived from the human tumour fragment. Considering the probable human origin of the endothelial cells from capillary blood vessels in the myxoma PDX, we conclude that this PDX model is an interesting model to study myxoma angiogenesis.

The Molecular Pathology of Odontogenic Tumors: Expanding the Spectrum of MAPK Pathway Driven Tumors

Odontogenic tumors comprise a heterogeneous group of lesions that arise from the odontogenic apparatus and their remnants. Although the etiopathogenesis of most odontogenic tumors remains unclear, there have been some advances, recently, in the understanding of the genetic basis of specific odontogenic tumors. The mitogen-activated protein kinases/extracellular signal-regulated kinases (MAPK/ERK) pathway is intimately involved in the regulation of important cellular functions, and it is commonly deregulated in several human neoplasms. Molecular analysis performed by different techniques, including direct sequencing, next-generation sequencing, and allele-specific qPCR, have uncovered mutations in genes related to the oncogenic MAPK/ERK signaling pathway in odontogenic tumors. Genetic mutations in this pathway genes have been reported in epithelial and mixed odontogenic tumors, in addition to odontogenic carcinomas and sarcomas. Notably, B-Raf proto-oncogene serine/threonine kinase (BRAF) and KRAS proto-oncogene GTPase (KRAS) pathogenic mutations have been reported in a high proportion of ameloblastomas and adenomatoid odontogenic tumors, respectively. In line with the reports about other neoplasms that harbor a malignant counterpart, the frequency of BRAF p.V600E mutation is higher in ameloblastoma (64% in conventional, 81% in unicystic, and 63% in peripheral) than in ameloblastic carcinoma (35%). The objective of this study was to review MAPK/ERK genetic mutations in benign and malignant odontogenic tumors. Additionally, such genetic alterations were discussed in the context of tumorigenesis, clinical behavior, classification, and future perspectives regarding therapeutic approaches.

Comparative Analysis Between Dentinogenic Ghost Cell Tumor and Ghost Cell Odontogenic Carcinoma: A Systematic Review

Dentinogenic ghost cell tumor (DGCT) and ghost cell odontogenic carcinoma (GCOC) form a spectrum of rare benign and malignant odontogenic neoplasms, respectively. The aim of this study was to perform a comparative systematic review of the clinicopathological, genetic, therapeutic, and prognostic features of DGCT and GCOC. The electronic search was performed until December 2020 on seven electronic databases. Case reports, series, and research studies with enough histopathological criteria for diagnosis and all genomic studies were included. Both DGCT and GCOC showed a male prevalence (p = 0.043), with mandibular and maxillary predilections, respectively (p = 0.008). Peripheral DGCT (DGCTp) affected most elderly people (p < 0.001), and central DGCT (DGCTc) and GCOC occurred mainly in younger individuals. Unilateral enlargement of maxilla or mandible was the most common clinical sign associated with a radiolucent or mixed image. Ameloblastomatous epithelium was often present in both neoplasms. Basaloid and large cells with vesicular nuclei were also frequently seen in GCOC. β-catenin expression and mutations (CTNNB1 gene) were found in DGCT and GCOC. Conservative surgery was mostly used for DGCTp, while radical resection was chosen for DGCTc and GCOC. High recurrence rates were found in DGCTc and GCOC. Metastasis occurred in 16.7% of GCOC cases and the 5-year survival rate was 72.6%. DGCT and GCOC share numerous clinicopathological features and demand a careful histopathological evaluation, considering the overlap features with other odontogenic tumors and the possibility of malignant transformation of DGCT. A strict regular post-operative follow-up is mandatory due to high recurrence rates and metastatic capacity in GCOC.

Patient-derived xenograft models for the study of benign human neoplasms

Preclinical models are a core feature of translational research, and patient-derived xenograft (PDX) models have increasingly been used with such purpose. PDX involves the transplantation of fresh human tumor samples into immunodeficient mice to overcome immunologic rejection. It is a valuable tool for basic as well as preclinical research, contributing to the establishment of models to characterize the neoplasms to drug screening and to allow the identification of therapeutic targets. The use of these models is justified because they retain the histological and genomic features of the primary tumor. PDX models are well described for malignant neoplasms, for which the advantages are clear and include the development of drug treatments. The establishment of malignant tumors PDX is undeniably important from a medical perspective. However, few studies have used such models for benign neoplasms. The use of PDX for benign neoplasm studies can help to clarify the pathobiology of these diseases, as well as invasion and malignant transformation mechanisms, which from a biological perspective is equally important to the study of malignant tumors. Therefore, the aim of this study is to review the current methodology for PDX model generation and to cover its main applications, focusing on benign neoplasms.

Odontogenic Myxoma: A 23-Year Retrospective Series of 38 Cases

Odontogenic myxoma (OM) is an uncommon benign odontogenic tumor arising in the jaw. Though it has slight histologic overlap with other entities, definitive diagnosis is imperative considering the tumor's aggressive nature, high recurrence rate, and necessity of radical surgical intervention in large-sized lesions. With IRB approval, a retrospective search of the University of Florida College of Dentistry Oral Pathology Biopsy Service archives from 1994 to 2017 for diagnosis of OM of the jaw was performed. Biopsy reports and original slides for each case were assessed and reviewed along with any accompanying radiographs to confirm the diagnosis. Immunohistochemical staining was utilized to exclude entities with histologic overlaps, such as intraosseous myxoid neurofibroma. A total of 38 cases were included. The patients' age ranged from 6 to 84 years, with a mean age of 37.47 years. Females comprised two-thirds of the cases (n = 25) versus males (n = 13). The mandible was the most affected at 60.5% (n = 23), followed by maxilla 39.4% (n = 15). Posterior jaw involvement was higher than anterior in both the mandible (n = 20 versus n = 3) and the maxilla (n = 11 versus n = 4). Most lesions presented clinically as expansile masses with variable radiographic appearance. The clinical impression from submitting providers included "gelatinous masses", abscesses, odontogenic lesions, fibro-osseous lesions, soft tissue or bone neoplasms, and reactive gingival lesions. A consensus of odontogenic myxoma as a diagnosis was rendered for 30 cases (79%), while in 8 cases (21%) that exhibited a more fibrous stroma was identified as fibromyxoma. OM may exhibit a varied demographic and clinical profile with a wide spectrum of histologic presentations. Pathologists should be sentient of this variability in order to arrive at an accurate diagnosis and correctly manage these patients.