Ameloblastoma: A Review of Recent Molecular Pathogenetic Discoveries

Differentially expressed extracellular matrix genes functionally separate ameloblastoma from odontogenic keratocyst

BACKGROUND

Ameloblastoma and odontogenic keratocyst (OKC) are odontogenic tumors that develop from remnants of odontogenic epithelium. Both display locally invasive growth characteristics and high predilection for recurrence after surgical removal. Most ameloblastomas harbor BRAFV600E mutation while OKCs are associated with PATCH1 gene mutation but distinctive indicators of ameloblastoma growth characteristics relative to OKC are still unclear. The aim of this study was to assess hub genes that underlie ameloblastoma growth characteristics using bioinformatic analysis, ameloblastoma samples and mouse xenografts of human epithelial-derived ameloblastoma cells.

METHODS

RNA expression profiles were extracted from GSE186489 gene expression dataset acquired from Gene Expression Ominibus (GEO) database. Galaxy and iDEP online analysis tools were used to identify differentially expressed genes that were further characterized by gene ontology (GO) and pathway analysis using ShineyGO. The protein-protein interaction (PPI) network was constructed for significantly upregulated differentially expressed genes using online database STRING. The PPI network visualization was performed using Cytoscape and hub gene identification with cytoHubba. Top ten nodes were selected using maximum neighborhood component, degree and closeness algorithms and analysis of overlap was performed to confirm the hub genes. Epithelial-derived ameloblastoma cells from conventional ameloblastoma were transplanted into immunocompromised mice to recreate ameloblastoma in vivo based on the mouse xenograft model. The top 3 hub genes FN1, COL I and IGF-1 were validated by immunostaining and quantitative analysis of staining intensities to ameloblastoma, OKC samples and mouse ameloblastoma xenografts tissues.

RESULTS

Seven hub genes were identified among which FN1, COL1A1/COL1A2 and IGF-1 are associated with extracellular matrix organization, collagen binding, cell adhesion and cell surface interaction. These were further validated by positive immunoreactivity within the stroma of ameloblastoma samples but both ameloblastoma xenograft and OKC displayed only FN1 and IGF-1 immunoreactivity while COL 1 was unreactive. The expression levels of both FN1 and IGF-1 were much lower in OKC relative to ameloblastoma.

CONCLUSION

This study further validates a differentially upregulated expression of matrix proteins FN1, COL I and IGF-1 in ameloblastoma relative to OKC. It suggests that differential stromal architecture and growth characteristics of ameloblastoma relative to OKC could be an interplay of differentially upregulated genes in ameloblastoma.

A Retrospective Analysis of 129 Ameloblastoma Cases: Clinical and Demographical Trends from a Single Institution

Ameloblastomas are benign neoplasms of the jaw, but frequently require extensive surgery. The aim of the study was to analyze the demographic and clinicopathological features of ameloblastoma cases at a single Oral and Maxillofacial Surgery group in the United States.

STUDY DESIGN

A retrospective chart review of patients evaluated for ameloblastoma between 2010 and 2020 at a single tertiary care center. Age, race, sex, tumor size, tumor location, and histological subtypes were recorded.

RESULTS

A total of 129 cases of ameloblastoma were recorded with a mean patient age of 42 ± 18.6 years (range 9-91 years old), male to female ratio 1.08:1. Ameloblastoma presenting in the mandible outnumbered maxilla in primary (118 to 8, respectively) and recurrent cases (8 to 1, respectively). There was a higher prevalence of ameloblastoma in Black patients (61.3%) with mean age of Black patients occurring at 40.5 years and the mean age of White patients occurring at 47.8 years and mean tumor size trended larger in the Black patients (15.7 cm2) compared to White patients (11.8 cm2).

CONCLUSION

Data suggests a strong influence of racial factors on the incidence of ameloblastoma, with regards to size, Black patients with ameloblastoma trended higher and more data is needed to clearly elucidate any relationship between the tumor size and race, as other factors may influence the size (such as time to discovery).

Exploring protein profiles and hub genes in ameloblastoma

Ameloblastoma (AM) is a prominent benign odontogenic tumor characterized by aggressiveness, likely originating from tooth-generating tissue or the dental follicle (DF). However, proteomic distinctions between AM and DF remain unclear. In the present study, the aim was to identify the distinction between AM and DF in terms of their proteome and to determine the associated hub genes. Shotgun proteomics was used to compare the proteomes of seven fresh-frozen AM tissues and five DF tissues. Differentially expressed proteins (DEPs) were quantified and subsequently analyzed through Gene Ontology-based functional analysis, protein-protein interaction (PPI) analysis and hub gene identification. Among 7,550 DEPs, 520 and 216 were exclusive to AM and DF, respectively. Significant biological pathways included histone H2A monoubiquitination and actin filament-based movement in AM, as well as pro-B cell differentiation in DF. According to PPI analysis, the top-ranked upregulated hub genes were ubiquitin C (UBC), breast cancer gene 1 (BRCA1), lymphocyte cell-specific protein-tyrosine kinase (LCK), Janus kinase 1 and ATR serine/threonine kinase, whereas the top-ranked downregulated hub genes were UBC, protein kinase, DNA-activated, catalytic subunit (PRKDC), V-Myc avian myelocytomatosis viral oncogene homolog (MYC), tumor protein P53 and P21 (RAC1) activated kinase 1. When combining upregulated and downregulated genes, UBC exhibited the highest degree and betweenness values, followed by MYC, BRCA1, PRKDC, embryonic lethal, abnormal vision, Drosophila, homolog-like 1, myosin heavy chain 9, amyloid beta precursor protein, telomeric repeat binding factor 2, LCK and filamin A. In summary, these findings contributed to the knowledge on AM protein profiles, potentially aiding future research regarding AM etiopathogenesis and leading to AM prevention and treatment.

Automatic segmentation of ameloblastoma on ct images using deep learning with limited data

BACKGROUND

Ameloblastoma, a common benign tumor found in the jaw bone, necessitates accurate localization and segmentation for effective diagnosis and treatment. However, the traditional manual segmentation method is plagued with inefficiencies and drawbacks. Hence, the implementation of an AI-based automatic segmentation approach is crucial to enhance clinical diagnosis and treatment procedures.

METHODS

We collected CT images from 79 patients diagnosed with ameloblastoma and employed a deep learning neural network model for training and testing purposes. Specifically, we utilized the Mask R-CNN neural network structure and implemented image preprocessing and enhancement techniques. During the testing phase, cross-validation methods were employed for evaluation, and the experimental results were verified using an external validation set. Finally, we obtained an additional dataset comprising 200 CT images of ameloblastoma from a different dental center to evaluate the model's generalization performance.

RESULTS

During extensive testing and evaluation, our model successfully demonstrated the capability to automatically segment ameloblastoma. The DICE index achieved an impressive value of 0.874. Moreover, when the IoU threshold ranged from 0.5 to 0.95, the model's AP was 0.741. For a specific IoU threshold of 0.5, the model achieved an AP of 0.914, and for another IoU threshold of 0.75, the AP was 0.826. Our validation using external data confirms the model's strong generalization performance.

CONCLUSION

In this study, we successfully applied a neural network model based on deep learning that effectively performs automatic segmentation of ameloblastoma. The proposed method offers notable advantages in terms of efficiency, accuracy, and speed, rendering it a promising tool for clinical diagnosis and treatment.

Immunohistochemical evaluation of yes-associated protein molecule in the odontogenic epithelium of different histopathological variants of ameloblastoma and unicystic ameloblastoma

Background

Ameloblastoma is one of the major odontogenic neoplasms with an invasive and recurrence potential. Its tumourigenesis and proliferative capacity can be attributed to the activation or inactivation of certain molecular signalling pathways. Hippo signalling pathway is known to regulate diverse physiological processes related to mitosis and organ growth and is an emerging tumour suppressor pathway, the dysfunction of which is implicated in various diseases including cancers. Yes-associated protein1 (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are the downstream effectors in the Hippo cascade, which on nuclear activation leads to cellular proliferation in various tumours.

Aim

The current study was undertaken to evaluate the expression of YAP in various histopathological variants of ameloblastoma and unicystic ameloblastoma.

Materials and Methods

Fifty formalin-fixed paraffin-embedded tissue samples of histopathologically diagnosed cases of ameloblastoma, and 10 histopathologically diagnosed cases of unicystic ameloblastoma were obtained from the departmental archives to evaluate the immunohistochemical expression of YAP both manually and by software analysis.

Results

More than 90% of cases of conventional ameloblastoma and unicystic ameloblastoma elicited positive expression of YAP. No statistical difference was found among different histopathological variants of conventional ameloblastoma. Significant difference between the means of all four quantitative score groups was observed.

Conclusion

In view of the modulating effect of YAP in tumourigenesis and its higher expression in ameloblastoma, further exploration of this molecule appears to be a promising area of research.

Machine learning-based radiomics for predicting BRAF-V600E mutations in ameloblastoma

Background

Ameloblastoma is a locally invasive and aggressive epithelial odontogenic neoplasm. The BRAF-V600E gene mutation is a prevalent genetic alteration found in this tumor and is considered to have a crucial role in its pathogenesis. The objective of this study is to develop and validate a radiomics-based machine learning method for the identification of BRAF-V600E gene mutations in ameloblastoma patients.

Methods

In this retrospective study, data from 103 patients diagnosed with ameloblastoma who underwent BRAF-V600E mutation testing were collected. Of these patients, 72 were included in the training cohort, while 31 were included in the validation cohort. To address class imbalance, synthetic minority over-sampling technique (SMOTE) is applied in our study. Radiomics features were extracted from preprocessed CT images, and the most relevant features, including both radiomics and clinical data, were selected for analysis. Machine learning methods were utilized to construct models. The performance of these models in distinguishing between patients with and without BRAF-V600E gene mutations was evaluated using the receiver operating characteristic (ROC) curve.

Results

When the analysis was based on radiomics signature, Random Forest performed better than the others, with the area under the ROC curve (AUC) of 0.87 (95%CI, 0.68-1.00). The performance of XGBoost model is slightly lower than that of Random Forest, and its AUC is 0.83 (95% CI, 0.60-1.00). The nomogram evident that among younger women, the affected region primarily lies within the mandible, and patients with larger tumor diameters exhibit a heightened risk. Additionally, patients with higher radiomics signature scores are more susceptible to the BRAF-V600E gene mutations.

Conclusions

Our study presents a comprehensive radiomics-based machine learning model using five different methods to accurately detect BRAF-V600E gene mutations in patients diagnosed with ameloblastoma. The Random Forest model's high predictive performance, with AUC of 0.87, demonstrates its potential for facilitating a convenient and cost-effective way of identifying patients with the mutation without the need for invasive tumor sampling for molecular testing. This non-invasive approach has the potential to guide preoperative or postoperative drug treatment for affected individuals, thereby improving outcomes.

BRAF V600E Mutation in Ameloblastoma: A Systematic Review and Meta-Analysis

The discovery that ameloblastoma has a high mutation incidence of BRAF V600E may enable a better investigation of pathophysiology. However, there is inconsistent evidence regarding this mutation occurrence and its association with clinical information. This systematic review and meta-analysis aim to pool the overall mutation prevalence of BRAF V600E in reported ameloblastoma cases and to determine its association with patient demographic and clinicopathological features. Following the PRISMA guidelines, a comprehensive article search was conducted through four databases (Scopus, Google Scholar, PubMed, and Web of Science). Seventeen articles between 2014 and 2022 met the inclusion criteria with 833 ameloblastoma cases. For each included study, the significance of BRAF V600E on the outcome parameters was determined using odd ratios and 95% confidence intervals. Meta-analysis prevalence of BRAF V600E in ameloblastoma was 70.49%, and a significant meta-analysis association was reported for those younger than 54 years old and in the mandible. On the contrary, other factors, such as sex, histological variants, and recurrence, were insignificant. As a result of the significant outcome of BRAF V600E mutation in ameloblastoma pathogenesis, targeted therapy formulation can be developed with this handful of evidence.

The diagnostic utility of BRAF VE1 mutation-specific immunohistochemistry in ameloblastoma

Ameloblastoma is a benign, locally aggressive odontogenic neoplasm with variable solid and cystic morphology. On account of its histologic variety, diagnostically challenging cases can bear resemblance to odontogenic keratocyst/keratocystic odontogenic tumor (KCOT) or dentigerous cyst (DC). BRAF^V600E mutation has been reported to be specific for and frequent in ameloblastoma, and this study evaluated the usefulness of immunohistochemistry (IHC) using the BRAF VE1 mutant-specific antibody as a diagnostic adjunct in this setting. We investigated 46 ameloblastomas, 30 KCOTs, and 30 DCs. BRAF VE1 IHC was performed on all cases and allele-specific polymerase chain reaction (AS-PCR) for BRAF^V600E mutation was performed on 30 ameloblastomas and any IHC-positive KCOT/DC. BRAF VE1 IHC was positive in 31/37 (83.8%) mandibular ameloblastomas but not in any maxillary ameloblastomas (0/9), KCOT (0/30), or DC (0/30). Equivocal staining was seen in 1/37 (3.3%) mandibular ameloblastomas. Of the 30 ameloblastomas subjected to AS-PCR, BRAF^V600E mutation was identified in 19/23 (82.6%) mandibular ameloblastomas and 0/7 (0.0%) maxillary ameloblastomas. BRAF^V600E mutant ameloblastomas were positive by IHC in 18/19 (94.7%) cases and equivocal in 1/19 (5.3%) cases. All 11 (100.0%) BRAF-wild type ameloblastomas were negative by IHC. BRAF VE1 is an excellent tool for the diagnosis of mandibular ameloblastoma but of limited utility in the maxilla, where it less commonly occurs and where BRAF^V600E mutation is considerably less frequent.

Contrast-enhanced multidetector computed tomography features and histogram analysis can differentiate ameloblastomas from central giant cell granulomas

BACKGROUND

No qualitative or quantitative analysis of contrast-enhanced computed tomography (CT) images has been reported for the differentiation between ameloblastomas and central giant cell granulomas (CGCGs).

AIM

To describe differentiating multidetector CT (MDCT) features in CGCGs and ameloblastomas and to compare differences in enhancement of these lesions qualitatively and using histogram analysis.

METHODS

MDCT of CGCGs and ameloblastomas was retrospectively reviewed to evaluate qualitative imaging descriptors. Histogram analysis was used to compare the extent of enhancement of the soft tissue. Fisher’s exact tests and Mann–Whitney U test were used for statistical analysis (P < 0.05).

RESULTS

Twelve CGCGs and 33 ameloblastomas were reviewed. Ameloblastomas had a predilection for the posterior mandible with none of the CGCGs involving the angle. CGCGs were multilocular (58.3%), with a mixed lytic sclerotic appearance (75%). Soft tissue component was present in 91% of CGCGs, which showed hyperenhancement (compared to surrounding muscles) in 50% of cases, while the remaining showed isoenhancement. Matrix mineralization was present in 83.3% of cases. Ameloblastomas presented as a unilocular (66.7%), lytic (60.6%) masses with solid components present in 81.8% of cases. However, the solid component showed isoenhancement in 63%. No matrix mineralization was present in 69.7% of cases. Quantitatively, the enhancement of soft tissue in CGCG was significantly higher than in ameloblastoma on histogram analysis (P < 0.05), with a minimum enhancement of > 49.05 HU in the tumour providing 100% sensitivity and 85% specificity in identifying a CGCG.

CONCLUSION

A multilocular, lytic sclerotic lesion with significant hyperenhancement in soft tissue, which spares the angle of the mandible and has matrix mineralization, should indicate prospective diagnosis of CGCG.

Identification of BRAF V600E mutation in odontogenic tumors by high-performance MALDI-TOF analysis

Odontogenic tumors are rare lesions with unknown etiopathogenesis. Most of them are benign, but local aggressiveness, infiltrative potential, and high recurrence rate characterize some entities. The MAP-kinase pathway activation can represent a primary critical event in odontogenic tumorigenesis. Especially, the BRAF V600E mutation has been involved in 80–90% of ameloblastic lesions, offering a biological rationale for developing new targeted therapies. The study aims to evaluate the BRAF V600E mutation in odontogenic lesions, comparing three different detection methods and focusing on the Sequenom MassARRAY System. 81 surgical samples of odontogenic lesions were subjected to immunohistochemical analysis, Sanger Sequencing, and Matrix-Assisted Laser Desorption/Ionization-Time of Flight mass spectrometry (Sequenom). The BRAF V600E mutation was revealed only in ameloblastoma samples. Moreover, the presence of BRAF V600E was significantly associated with the mandibular site (ρ = 0.627; P value <0.001) and the unicystic histotype (ρ = 0.299, P value <0.001). However, any significant difference of 10-years disease-free survival time was not revealed. Finally, Sequenom showed to be a 100% sensitive and 98.1% specific, suggesting its high-performance diagnostic accuracy. These results suggest the MAP-kinase pathway could contribute to ameloblastic tumorigenesis. Moreover, they could indicate the anatomical specificity of the driving mutations of mandibular ameloblastomas, providing a biological rational for developing new targeted therapies. Finally, the high diagnostic accuracy of Sequenom was confirmed.

The Expression of Selected Wnt Pathway Members (FZD6, AXIN2 and β-Catenin) in Canine Oral Squamous Cell Carcinoma and Acanthomatous Ameloblastoma

The Wnt signaling pathway is well known to be involved in many types of human cancer; however, in veterinary medicine, the investigation of individual Wnt members' expression, and their role in or association with oral tumor pathogenesis, is still underevaluated. We aim to determine the expression pattern of Frizzled-6 (FZD6) as one of the Wnt receptors in two of the most common canine oral neoplastic lesions-canine oral squamous cell carcinoma (COSCC) and canine acanthomatous ameloblastoma (CAA). While COSCC is a malignant tumor with aggressive biological behavior and a tendency to metastasize, CAA is a benign tumor with high local invasiveness. In CAA, the expression of FZD6 was mostly located in the center of the epithelial tumorous tissue, and cells exhibiting features of squamous metaplasia were strongly positive. In well-differentiated COSCC, FZD6 was expressed in the tumorous epithelium as well as the tumorous stroma. There was a negative correlation between cytokeratin expression and FZD6 expression in COSCC, where the central parts of the epithelial tumorous tissue were often FZD6-negative. The non-differentiated COSCC with low expression of cytokeratin exhibited a diffuse FZD6 signal. The invasive front with areas of tumor budding exhibited high FZD6 expression with a loss of cytokeratin expression. Moreover, the expression of β-catenin and AXIN2 was increased in comparison to gingiva. In conclusion, our study revealed significant differences in the expression patterns and the levels of FZD6 between COSCC and CAA, indicating the differential engagement of the Wnt pathway in these tumors.

Odontogenic fibroma amyloid-variant: a typical case and brief considerations about mimickers

The World Health Organization's (WHO) updated classification of head and neck tumors (2017) defined odontogenic fibroma as a rare neoplasm. In this report, we describe an unusual, typical and rare variant of a central odontogenic fibroma with diffuse amyloid-like protein stromal deposition, and discuss the differential diagnosis with other entities. Radiographically, this lesion presented as a well-defined radiolucency of the mandible, partially cystic. Histologically, the lesion showed a unique confluence of odontogenic epithelial rests in a moderately cellular connective tissue. Immunohistochemical staining highlighted a mixture of benign epithelial and Langerhans cells within connective tissue with diffuse amyloid-like stromal deposition. The importance of recognizing this variant of odontogenic fibroma is due to its benign prognosis and clinical course.

Enucleation and surgical stent as a treatment strategy for a large unicystic ameloblastoma: Case report and review of literature

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Ameloblastoma has a locally invasive and aggressive nature and high recurrence rate.

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A conservative approach and a radical resection approach have been suggested.

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Radical resection may lead to esthetic, functional, and psychological sequelae.

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First use of surgical stent with conservative management for ameloblastoma.

Introduction

Ameloblastoma is a benign neoplasm of odontogenic origin with local invasive characteristics and a high recurrence rate. It compromised 1% of the jaw's cysts and tumors with only 10–15% in children.

Presentation of case

A 14-year-old boy sought treatment for a painless swelling involving the right side of the face started one year ago. The intra-oral examination displayed a firm mass associated with 46, 47 teeth, and the angle of the mandible. The radiographic examination revealed a large well-defined homogeneous radiolucency extending from the 46 region to involve the angle and extending towards the coronoid and condylar processes. An incisional biopsy confirmed the diagnosis of unicystic ameloblastoma. Treatment was planned according to the patient’s age: Phase I: Surgical enucleation. Phase II: Construction and insertion of a surgical stent. Phase III: Construction of a transitional acrylic Kennedy class II partial denture. Phase IV: the patient is scheduled for a definitive implant-supported prosthesis at 18 years old.

Discussion

The management of ameloblastoma is influenced by the age of the patient, the extension, duration, and position of the lesion, and the histopathological variants. Several authors recommended enucleation as a conservative treatment approach to eliminate the esthetical, functional, and psychological squeals associated with the radical approach. The use of a surgical stent protects the enucleated cavity and promote tissue healing.

Conclusion

Enucleation and subsequent surgical stent not only eliminates the disease, but also preserves the bone structure, prevents the facial disfigurement, and significantly improve the patient’s esthetic, mastication, oral health, and quality of life.

An integrative analysis of genome-wide methylation and expression in ameloblastoma: A pilot study

OBJECTIVE

DNA methylation regulates the expression of various genes involved in tumorigenesis. Ameloblastoma is a benign odontogenic jaw tumor. It is locally aggressive with a high level of recurrence. A delay in treatment can lead to severe facial disfigurement. To the best of our knowledge, this is the first integrated analysis of DNA methylation and gene expression in ameloblastoma with the aim to identify genes that may be regulated by DNA methylation.

MATERIALS AND METHODS

We used an Infinium MethylationEPIC array to measure genome-wide methylation and the Illumina HiSeq platform to obtain gene expression data in ameloblastoma tissues from five patients and dental follicles from three healthy subjects. An integration analysis was performed using City of Hope CpG Island Analysis Pipeline software.

RESULTS

We identified 25,255 differentially methylated CpG sites and 17 differentially methylated CpG islands; six of the islands were negatively correlated with the expression of BAIAP2, DUSP6, FGFR2, FOXF2, NID2, and PAK6. Pyrosequencing and immunostaining techniques were further used to validate FGFR2, NID2, and PAK6.

CONCLUSIONS

This analysis identifies a group of novel genes that may be regulated by DNA methylation and will possibly lead to new insights into the pathology and invasion mechanism of ameloblastoma.

Immunohistochemical Detection of Nerve Growth Factor (NGF) in Follicular and Plexiform Ameloblastoma - A Novel Study

Background:

Ameloblastoma is the second most common odontogenic tumor that holds a unique position among benign tumors due to its locally destructive and invasive nature. The differed tumor biology behind follicular and plexiform ameloblastoma is always an enigma. Nerve growth factor (NGF), a neurotrophin that plays a major role during odontogenesis, could also possibly play a role in the pathogenesis of odontogenic tumors such as ameloblastoma. With this background, the study was aimed to investigate the expression of NGF in follicular and plexiform ameloblastoma.

Objectives:

The objectives of this study were to analyze the immunohistochemical expression pattern of NGF in ameloblastoma and to compare the immunohistochemical expression pattern of NGF among the follicular and plexiform histological types of ameloblastoma.

Materials and Methods:

Forty histological sections of ameloblastomas (20 follicular and 20 plexiform) were stained immunohistochemically with anti-human NGF mouse IgG monoclonal antibody and the staining was analyzed statistically.

Results:

Almost all the 40 ameloblastoma samples (20 follicular and 20 plexiform) showed positive immunoreactivity to NGF. Both peripheral pre-ameloblast-like tall columnar cells and central stellate-reticulum-like cells showed positive reactivity. The pattern of staining was membranous in the immunoreactive cells. The χ² value for the immunoexpression between follicular and plexiform ameloblastoma was statistically significant with a P value <0.002. A possible mechanism has been proposed after studying the results with the downstream pathways obtained from literature.

Conclusion:

The pattern of expression of NGF is seen in both follicular and plexiform ameloblastoma. But the intensity is more in plexiform than that of follicular ameloblastoma.

High frequency of BRAF V600E mutation in Iranian population ameloblastomas

Background

Ameloblastoma is a common locally invasive but slow-growing neoplasm of the jaws with an odontogenic origin. Association between BRAF V600E mutation and clinicopathologic features and behavior of ameloblastoma remains controversial. This study aimed to evaluate BRAF V600E gene mutation and expression of its related proteins with clinicopathologic parameters in conventional ameloblastoma.

Material and Methods

50 Formalin-fixed paraffin-embedded blocks were included in this study. Immunohistochemistry was done using rabbit monoclonal BRAF V600E mutation-specific antibody VE1. Quantitative real-time polymerase chain reaction assay was used for evaluating of BRAF V600E mutation.

Results

Expression of BRAF V600E antibody was Positive in 42 out of 50 cases (84%). 46 (92%) out of 50 specimens showed BRAF V600E mutation. There were 13 cases of recurrence (26%). 3 out of 4 cases with negative mutations did not show recurrence.

Conclusions

We report the highest frequency (92%) of BRAF V600E mutation in ameloblastomas in the Iranian population. Although there was not a significant association between BRAF V600E‑positive immunoexpression and recurrence and clinicopathologic parameters, its high frequency could emphasize its role as a therapeutic marker in the future.

Key words:Conventional ameloblastoma, BRAF V600E, recurrence.

Immunohistochemical detection of Tyrosine Kinase receptor (TrK) in follicular and plexiform ameloblastoma - A novel study

Objectives:

The objective is to analyze the immunohistochemical expression pattern of tyrosine kinase receptor (TrK) in ameloblastoma and to compare the immunohistochemical expression pattern of TrK among the histological types of ameloblastoma, follicular and plexiform patterns.

Materials and Methods:

Forty ameloblastomas (20 follicular and 20 plexiform) were immunostained with anti-human TrK mouse IgG monoclonal antibody, and the pattern of staining is statistically analyzed.

Results:

Total 20 (4 follicular and 16 plexiform) out of 40 ameloblastomas showed immunoreactivity to TrK. Only the peripheral preameloblast like tall columnar cells showed reactivity, whereas the stellate reticulum like cells is immunonegative. The staining pattern was membranous in the immunoreactive cells. The Chi-square value for the immunoexpression between follicular and plexiform ameloblastoma was statistically significant with a P < 0.005. The results were studied with the downstream pathways from the literature, and a possible mechanism has been proposed.

Conclusion:

The expression pattern of TrK is found to be more in plexiform ameloblastoma than follicular ameloblastoma.

LGR5+ epithelial tumor stem-like cells generate a 3D-organoid model for ameloblastoma

Ameloblastoma (AM) is a benign but locally aggressive tumor with high recurrences. Currently, underlying pathophysiology remains elusive, and radical surgery remains the most definitive treatment with severe morbidities. We have recently reported that AM harbors a subpopulation of tumor epithelial stem-like cells (AM-EpiSCs). Herein, we explored whether LGR5⁺ epithelial cells in AM possess stem-like cell properties and their potential contribution to pathogenesis and recurrence of AM. We found that LGR5 and stem cell-related genes were co-expressed in a subpopulation of AM epithelial cells both in vivo and in vitro, which were enriched under 3D-spheroid culture. As compared to LGR5⁻ counterparts, LGR5⁺ AM epithelial cells showed increased expression of various EMT- and stemness-related genes, and functionally, exhibited increased capacity to form 3D-spheroids and generate human tumor 3D organoids, which recapitulated the histopathologic features of distinct subtypes of solid AM, thus, contributing a useful human tumor platform for targeted therapeutic screening. Treatment with a selective BRAF^V600E inhibitor, vemurafenib, unexpectedly enriched the subpopulation of LGR5⁺ AM-EpiSCs in tumor 3D organoids, which may have explained therapeutic resistances and recurrences. These findings suggest that LGR5⁺ AM-EpiSCs play a pivotal role in pathogenesis and progression of AM and targeted inhibition of both BRAF and LGR5 potentially serves a novel nonsurgical adjuvant therapeutic approach for this aggressively benign jaw tumor.

SOX2 and BCL-2 Expressions in Odontogenic Keratocyst and Ameloblastoma

Background

The purpose of this experimental study was to compare the immunohistochemical expression of SOX2 and BCL-2 in Odontogenic Keratocyst (OKC) and Ameloblastoma (AB) specimens, and to identify a possible correlation in their expression.

Material and Methods

Immunohistochemical analysis was performed to evaluate SOX2 and BCL-2 expression in OKC (n = 20) and AB (n = 20). The immunoexpression was analyzed by a quantitative and qualitative scoring system. The comparison between the immunoexpression of SOX 2 and BCL-2 was assessed by the Mann-Whitney U-test. Spearman’s correlation coefficient evaluated the correlation between SOX2 and BCL-2 expressions.

Results

SOX2 and BCL-2 expression was observed in all specimens of OKC in the full thickness of the epithelium lining. SOX2 immunostaining was higher in OKC, in comparison with AB samples (P<0.05). BCL-2 immunostaining between OKC and AB was not statistically significant. There was no significant correlation between SOX2 and BCL-2 in OKC and AB specimens.

Conclusions

SOX2 and BCL-2 expressions in OKC may suggest their relationship with the biological behavior of this lesion, and the higher expression of SOX2 might be an upstream influence on the Hh signaling pathway.

Key words:Odontogenic keratocyst; Ameloblastoma; Odontogenic tumor; SOX2; BCL-2.

Discovery of novel molecular characteristics and cellular biological properties in ameloblastoma

Ameloblastoma is a rare odontogenic benign tumor accounting for less than 1% of head and neck tumors. Advanced next generation sequencing (NGS) analyses identified high frequency of BRAF V600E and SMO L412F mutations in ameloblastoma. Despite the existence of whole genomic sequence information from patients with ameloblastoma, entire molecular signature of and the characteristics of ameloblastoma cells are still obscure. In this study, we sought to uncover the molecular basis of ameloblastoma and to determine the cellular phenotype of ameloblastoma cells with BRAF mutations. Our comparative cDNA microarray analysis and gene set enrichment analysis (GSEA) showed that ameloblastoma exhibited a distinct gene expression pattern from the normal tissues: KRAS-responsive gene set is significantly activated in ameloblastoma. Importantly, insulin like growth factor 2 (IGF2), a member of KRAS-responsive genes, enhances the proliferation of an ameloblastoma cell line AMU-AM1 with BRAF mutation. In addition, Toll-like receptor 2 (TLR2) knockdown readily inactivated KRAS-responsive gene sets as well as increases caspase activities, suggesting that TLR2 signaling may mediate cell survival signaling in ameloblastoma cells. Collectively, the findings may help to further clarify the pathophysiology of ameloblastoma and lead to the development of precision medicine for patients with ameloblastoma.

Peripheral ameloblastoma of the gingiva

Peripheral Ameloblastoma (PA) is a benign odontogenic tumor, arising from the cell rest of Serres, reduced enamel epithelium and basal cells of the surface epithelium. Peripheral ameloblastoma is a rare odontogenic neoplasm occurring commonly in the mandibular gingiva. PA clinically resembles other peripherally occurring lesions like pyogenic granuloma, peripheral ossifying fibroma, peripheral giant cell granuloma, and squamous papilloma. The recurrence rate of PA is 16-19% which demands a straight follow up. We report a case of recurrent peripheral ameloblastoma occurring in a 72-year old male located in the mandibular lingual gingiva in relation to the 44, 45 element's regions. The patient had a primary lesion excised from the same site 6 years before which was diagnosed as ameloblastoma.

BRAF V600E expression in ameloblastomas-A 36-patient cohort from Helsinki University Hospital

OBJECTIVES

We aimed to investigate BRAF V600E percentage immunohistochemically in ameloblastomas of a single institute cohort. We were interested if age, location, histological properties, or tumor recurrence depend on the BRAF status.

SUBJECTS, MATERIALS AND METHODS

We had 36 formalin-fixed, paraffin-embedded ameloblastoma tissue samples of patients treated at the Helsinki University Hospital between the years 1983-2016. Tissue sections underwent immunohistochemistry by Ventana BenchMark XT immunostainer using Ms Anti-Braf V600E (VE1) MAB. We used R 3.4.2 and RStudio 1.1.383 to conduct statistical analysis for BRAF positivity and earlier onset as well as tumor location. We used chi-squared tests and 2-by-2 table functions to determine connections between BRAF positivity and recurrence, growth pattern, and type.

RESULTS

BRAF-positive tumors occurred in younger patients compared to BRAF-negative tumors (p = 0.015) and they located mostly to the mandible (p < 0.001). Growth patterns were limited to two in BRAF-negative tumors when BRAF-positive tumors presented with one to four growth patterns (p = 0.02). None of the maxillary tumors showed BRAF positivity and of these, 72.2% recurred.

CONCLUSIONS

An immunohistochemical BRAF marker could be a beneficial tool to predict the outcome of patients with this aggressive, easily recurring tumor.

Update on Odontogenic Tumors: Proceedings of the North American Head and Neck Pathology Society

Odontogenic tumors are rare entities, often derived from the epithelial remnants in the gnathic bones following odontogenesis. This brief manuscript will seek to address recent developments pertaining to odontogenic tumors as well as particularly uncommon odontogenic tumors and the difficulties in their diagnosis.

Bcl-2 is a prognostic marker and its silencing inhibits recurrence in ameloblastomas

OBJECTIVES

Ameloblastomas are the most common odontogenic epithelial tumors with high recurrence rate. The aim of this study was to identify apoptosis-related genes with recurrence of ameloblastomas and to evaluate its feasibility as a prognostic marker and as a target molecule preventing from recurrence.

MATERIALS AND METHODS

Public microarray data were analyzed. To evaluate their expression in ameloblastoma patients, immunohistochemical staining was performed in 89 human ameloblastoma tissues. Quantitative PCR was performed by use of ameloblastoma cell line (AM-1). Fluorescence activated cell sorting analysis and western blotting were conducted following transfection with siRNA. Further, AM-1 cells were implanted in the renal subcapsular layer of immunodeficient mice.

RESULTS

Microarray data analysis revealed that osteoprotegerin (OPG) and B-cell lymphoma 2 (Bcl-2) were the two most upregulated genes in ameloblastoma. Only Bcl-2 expression was significantly (p = 0.020) associated with recurrence in conservative treatment group (n = 17) among 89 patients. Silencing of Bcl-2 increased apoptosis in AM-1 cells in vitro and inhibited tumor nodule formation of AM-1 cells in vivo.

CONCLUSION

These results suggest that Bcl-2 expression is a useful biomarker to predict recurrence of ameloblastomas, and as a therapeutic target molecule to prevent recurrence of ameloblastoma.

Ameloblastic carcinoma: a clinicopathologic analysis of cases seen in a Nigerian Teaching Hospital and review of literature

Introduction

Ameloblastic carcinoma is a rare malignant odontogenic neoplasm that exhibits histological features of ameloblastoma in combination with cytological atypia. It may arise de novo or secondarily through malignant de-differentiation of pre-existing ameloblastoma or odontogenic cyst. Secondary ameloblastic carcinomas often results from repeated surgical intervention, which is a mainstay of odontogenic tumor management in resource limited settings. To date, relatively few cases of ameloblastic carcinomas have been reported and many cases have been misdiagnosed as ameloblastoma. This is due to its wide range of clinicopathological feature which range from indolent to aggressive. It may present as an aggressive ulcerated mass or as a simple cystic lesion; hence, it often challenging to delineate from its benign counterpart, ameloblastoma.

Methods

this study reviewed the clinicopathological data on 157 cases of odontogenic tumors diagnosed over a 10 years period from the pathology archive of the Oral Pathology Unit of Obafemi Awolowo University Teaching Hospital Complex (OAUTHC), Ile-Ife, Nigeria.

Results

of all these cases, we identified that 64.9% were Ameloblastomas, while 8.3% were ameloblastic carcinomas. Primary subtypes of ameloblastic carcinoma constituted 23.08%, while 69.23% of the cases were of the secondary subtype. We also found that the secondary subtype of ameloblastic carcinomas showed a higher mean duration value of 7.7 years. Most lesions were found in posterior mandible and presented with ulceration, perforation and ill-defined borders radiographically.

Conclusion

this study is among the few that have documented higher frequency of secondary ameloblastic carcinoma in the scientific literature.

Malignant ameloblastoma: a challenging diagnosis

Ameloblastoma is an uncommon and locally aggressive, benign, odontogenic tumor, with local recurrence when not adequately excised. A rare variant of this neoplasm with the benign features but accompanied with metastases has been described. This rare variant is malignant ameloblastoma and is known to have a poor prognosis. We present the case of a young woman who had recurrent mandibular tumors, which were resected twice and histologically reported as ameloblastoma. Four years later, she presented with pulmonary metastasis and atelectasis. A review of the literature on this very rare neoplasm was also performed.

Clinical benefit and radiological response with BRAF inhibitor in a patient with recurrent ameloblastoma harboring V600E mutation

Background

Ameloblastoma is a slow-growing neoplasm of the jaw, for which the standard treatment is surgical removal of the lesion with high recurrence rates and elevated morbidity. Systemic therapy is not established in the literature.

Case presentation

We present a case of a 29-year-old woman diagnosed with an ameloblastoma of the left mandible who had been subjected to several surgical procedures over twenty years due to multiple local recurrences. Molecular testing revealed a BRAF V600E mutation, and vemurafenib was started. She experienced complete resolution of symptoms related to the disease, and image scans evidenced continuous shrinkage of the neoplastic lesion after eleven months of therapy.

Conclusion

This is the first report showing clinical benefit and radiological response with vemrafenib for recurrent ameloblastoma. Targeted therapy addressing BRAF V600E mutation has the potential to change clinical practice of this rare disease.

Malignant Transformation of a Desmoplastic Ameloblastoma to Squamous Cell Carcinoma: A Case Report

Ameloblastomas are the most common odontogenic tumors, excluding odontomas. Several morphologic variants have been described including follicular, plexiform, acanthomatous, granular cell, basaloid and desmoplastic. Desmoplastic ameloblastoma differs from other conventional ameloblastomas microscopically, clinically, and radiographically. Ameloblastic carcinoma, the malignant counterpart of ameloblastoma is characterized by cytologic features of malignancy combined within the overall histologic features of conventional ameloblastoma. Malignant transformation of ameloblastoma to squamous cell carcinoma is a controversial subject. Here we report a case of a desmoplastic ameloblastoma with malignant transformation to squamous cell carcinoma in a 49 year old African American man. The patient underwent tumor resection and radiation therapy with no evidence of disease recurrence or progression 16 months post operatively. To our knowledge malignant transformation of a desmoplastic ameloblastoma to squamous cell carcinoma has not so far been reported. This observation may lend some support to the argument that desmoplastic ameloblastoma is phenotypically and biologically distinct entity.

The landscape of genetic alterations in ameloblastomas relates to clinical features

Ameloblastoma is a mostly benign, but locally invasive odontogenic tumor eliciting frequent relapses and significant morbidity. Recently, mutually exclusive mutations in BRAF and SMO were identified causing constitutive activation of MAPK and hedgehog signaling pathways. To explore further such clinically relevant genotype-phenotype correlations, we here comprehensively analyzed a large series of ameloblastomas (98 paraffin block of 76 patients) with respect to genomic alterations, clinical presentation, and histological features collected from the archives of three different pathology centers in France, Germany, and Turkey. In good agreement with previously published data, we observed BRAF mutations almost exclusively in mandibular tumors, SMO mutations predominantly in maxillary tumors, and single mutations in EGFR, KRAS, and NRAS. KRAS, NRAS, PIK3CA, PTEN, CDKN2A, FGFR, and CTNNB1 mutations co-occurred in the background of either BRAF or SMO mutations. Strikingly, multiple mutations were exclusively observed in European patients, in solid ameloblastomas and were associated with a very high risk for recurrence. In contrast, tumors with a single BRAF mutation revealed a lower risk for relapse. We here establish a comprehensive landscape of mutations in the MAPK and hedgehog signaling pathways relating to clinical features of ameloblastoma. Our data suggest that ameloblastomas harboring single BRAF mutations are excellent candidates for neo-adjuvant therapies with combined BRAF/MEK inhibitors and that the risk of recurrence maybe stratified based on the mutational spectrum.

Low frequency of BRAF V600E immunoexpression in mandibular ameloblastomas: An institutional study

Background:

Ameloblastoma is an uncommon, benign neoplasm of odontogenic epithelium commonly affecting the posterior mandible (almost 80%) particularly in the molar/ramus region, with occasional tumors involving the maxilla. Recently, there has been much interest generated after the reports of BRAF V600E mutations in ameloblastomas with a frequency of 46%–80% using both molecular as well as immunohistochemical (IHC) techniques. We sought to assess the presence of BRAF V600E expression in ameloblastomas in Indian patients and correlate the same with clinical behavior and histological variants by performing IHC analysis with anti-BRAF V600E antibody.

Materials and Methods:

Thirty formalin-fixed paraffin-embedded tissues of mandibular ameloblastomas were examined by anti-BRAF V600E antibody and correlated with clinicopathologic and histological parameters. Cytoplasmic staining of neoplastic epithelium was considered positive for BRAF V600E expression.

Statistical Analysis:

Data analysis was performed using Chi-square test and Student's t-test with statistical software IBM SPSS statistics 20.0.

Results:

BRAF V600E antibody showed positive expression only in 33.3% (10/30) cases. About 66.7% (4/6) recurrent cases and 63.6% (7/11) plexiform cases showed statistically significant association of P = 0.05 and P = 0.021, respectively, among cases with positive BRAF V600E immunoexpression.

Conclusion:

We report the lowest frequency (33.3%) of BRAF V600E immunoexpression in mandibular ameloblastomas in Indian population. However, a significant association of BRAF V600E-positive immunoexpression with recurrence and plexiform pattern could underline its role as a therapeutic marker for ameloblastoma.

Orbital invasion of ameloblastoma: A systematic review apropos of a rare entity

Purpose

Ameloblastoma is a non-encapsulated and slow-growing tumor with high recurrence rate. Orbital involvement by this neoplasm is an extremely rare entity. In this study, we present a systematic review on this situation along with clinical and paraclinical features of a case.

Methods

An electronic search was conducted on major medical sources. Data of the cases in the literature in addition to our own case were extracted, summarized, and statistically analyzed.

Results

A total of 36 other cases from 20 relevant studies were also reviewed. Review topics included epidemiology, clinical presentation, pathologic features, differential diagnosis, imaging, treatment, and prognosis. We provided a five-year history of a 50-year-old man with orbital/skull base invasion of plexiform maxillary ameloblastoma.

Conclusions

Maxillary ameloblastoma is a locally aggressive neoplasm, and physicians must be alert to the biologic behavior of this tumor to detect any invasion to critical structures such as orbit and cranium. Orbital ameloblastoma causes significant morbidity and mortality. We advocate meticulous patient follow-up with regular clinical examinations and paraclinical work-up for timely detection of any invasion or recurrence. The best must be done to avoid extensions by aggressive removal of maxillary ameloblastoma.

The anecdote of viral etiopathogenia in ameloblastoma and odontogenic keratocyst: Why don't we let it go?

BACKGROUND

Ameloblastoma (AM) and odontogenic Keratocyst (OKC) are destructive odontogenic lesions of the gnathion. Although their exact pathogeneses are not yet totally understood, the viral etiopathogenesis in AM and KCOT has been proposed. True to syndromic keratocystic odontogenic tumor (sKCOT) and non-syndromic OKC is the high recurrence rate.

OBJECTIVES

Given that shared pathways trailed by AM and by sKCOT/OKC have been suggested, this study, however, contrasts the expression of AM and OKC for viral antibodies.

METHOD

A total of archival 80 paraffin blocks of cases of parakeratinized odontogenic keratocyst (non-syndromic KCOTs) and of ameloblastomas (n = 40 for each) were included in this study to be sectioned and stained for two immunohistochemical markers: anti-human papillomavirus and Epstein-Barr virus-encoded latent membrane protein.

RESULTS

All the submitted cases of AM and parakeratinized OKC were negative for both markers: anti-HPV and anti-LMP-1.

CONCLUSIONS

Although results could have been biased, given the same ethnic group and territory examined in this study, all cases were negative for both markers. Therefore, the viral contribution to the etiopathogenesis in AM and OKC could not be established in this study.

Update from the 4th Edition of the World Health Organization Classification of Head and Neck Tumours: Odontogenic and Maxillofacial Bone Tumors

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.

BRAF-V600E expression correlates with ameloblastoma aggressiveness

AIMS

The aim of this study was to investigate whether the expression of BRAF-V600E determines an aggressive clinical and molecular presentation of ameloblastoma.

METHODS AND RESULTS

Ninety-three cases of solid ameloblastomas were arranged in a 1.0-mm tissue microarray (TMA) block. Immunohistochemistry against a large panel of cytokeratins (CK), epidermal growth factor receptor (EGFR), parathyroid hormone-related peptide (PTHrP), syndecan-1, Ki67, p53 and BRAF-V600E were performed. Clinicopathological parameters, including sex, age, tumour size, tumour duration, tumour location, treatment, recurrences, radiographic pattern, vestibular/lingual and basal cortical plates disruption and follow-up data, were obtained from patients' medical records. Immunoexpression of BRAF-V600E was investigated in 73 cases that remained available in TMA sections. Our results indicated that 46.6% (34 cases) demonstrated cytoplasm positivity (six weak and 28 strong positivity). BRAF-V600E expression was associated significantly with the expression of CK8 (P = 0.00077), CK16 (P = 0.05), PTHrP (P = 0.0082) and p53 (P = 0.0087). Additionally, a significant association was seen with the presence of recurrences (P = 0.0008), multilocular radiographic appearance (P = 0.044) and disruption of basal bone cortical (P = 0.05). Univariate analysis showed that BRAF-positive cases (P = 0.001), EGFR-negative/weak positive cases (P = 0.03) and multilocular tumours (P = 0.04) had a significantly lower disease-free survival rate, but these parameters were not considered independent prognostic factors in the multivariate analysis (P > 0.05).

CONCLUSIONS

Our findings suggest an association of BRAF-V600E with parameters of a more aggressive behaviour of ameloblastoma, supporting the future use of BRAF inhibitors for targeted therapy of this neoplasm.

Immunohistochemical biomarkers in ameloblastomas

Ameloblastoma is an aggressive odontogenic tumour, which is locally invasive and highly recurrent. Studies show that ameloblastoma is a benign odontogenic neoplasia, being relatively rare and occasionally presenting behaviour of malignant lesions. In addition to these particularities, the histological diagnosis of ameloblastoma can be challenging when the tumour shows high rates of mitosis, absence of nuclear pleomorphism, basilar hyperplasia and neural invasion. In order to help in the diagnosis, prognosis and treatment of this neoplasia, some immunohistochemical markers were shown to be associated with tumoural epithelium. The identification of these markers as well as of their association with clinical signs can be useful to elaborate more efficient treatment strategies and to control this pathology, including improvement of the quality of life of patients affected by this neoplasia. This article aims to review some markers associated with specific molecular pathways, bone remodelling, cell proliferation, apoptosis, cell signalling and tumour suppression.

Ameloblastic Carcinoma: A Report of Three Cases

Malignant odontogenic tumours are rare and represent approximately 1% of all oral malignancies. Ameloblastic carcinoma is a rare odontogenic tumour, which is aggressive in nature with extensive local bone destruction that has retained the features of ameloblastic differentiation and also exhibits cytological features of malignancy. It occurs primarily in the mandible in a wide range of age groups. It may arise de-novo or in pre-existing ameloblastoma or odontogenic cyst. The purpose of this report is to present three cases of ameloblastic carcinoma with varying presentations as central and peripheral entities.

Molecular Signaling in Benign Odontogenic Neoplasia Pathogenesis

Several molecular pathways have been shown to play critical roles in the pathogenesis of odontogenic tumors. These neoplasms arise from the epithelial or mesenchymal cells of the dental apparatus in the jaw or oral mucosa. Next generation genomic sequencing has identified gene mutations or single nucleotide polymorphisms associated with many of these tumors. In this review, we focus on two of the most common odontogenic tumor subtypes: ameloblastoma and keratocystic odontogenic tumors. We highlight gene expression and protein immunohistological findings and known genetic alterations in the hedgehog, BRAF/Ras/MAPK, epidermal growth factor receptor, Wnt and Akt signaling pathways relevant to these tumors. These various pathways are explored to potentially target odontogenic tumors cells and prevent growth and recurrence of disease. Through an understanding of these signaling pathways and their crosstalk, molecular diagnostics may emerge as well as the ability to exploit identified molecular differences to develop novel molecular therapeutics for the treatment of odontogenic tumors.