Review article: Current concepts of ameloblastoma pathogenesis

Maxillary Ameloblastoma in an Asiatic Black Bear (Ursus thibetanus)

An approximately 30-year-old intact female Asiatic black bear (Ursus thibetanus) was presented for annual examination and a history of ptyalism. A large 9.5 cm × 5 cm × 5 cm, firm, round mass was identified attached to the hard palate on physical examination. A computed tomography scan was performed, and the heterogeneous, mineral-attenuating mass was seen arising from the right aspect of the palatine bone and extending rostrally to the level of the last maxillary molars, caudally into the oropharynx, and dorsally into the nasal choana. Surgical debulking was performed to remove the portion of the mass within the oral cavity. Histopathologic analysis was consistent with a keratinizing ameloblastoma. Nine months postoperatively, the patient was asymptomatic for the tumor. The patient was euthanized 23-months postoperatively, and severe diffuse pustular dermatitis, growth of the ameloblastoma on the hard palate, and various degenerative and aging changes were noted on necropsy at that time. This is the first report of an ameloblastoma in a member of the Ursidae family.

Clinicoradiologic features of ameloblastomas: A single-centre study of 155 cases

BACKGROUND

The purpose of the current study was to report on the clinical presentation and radiologic features of 155 cases of ameloblastoma (AB), representing a detailed, large, single-centre radiologic study.

METHODS

Histologically confirmed cases were reviewed over 11 years. Demographic and clinical data were retrieved from the patient's records. Radiologic information was analysed from available radiographs. The radiologic features of ABs were assessed according to the mean age of presentation and the mean duration of the lesion. The distinguishing radiologic features between adults/children and sex were also evaluated.

RESULTS

A statistically significant correlation existed between loss of border demarcation and advanced mean age. Multilocular lesions were markedly more common in adults compared to children. Multilocular ABs were associated with increased lesion duration and advanced mean age. Radiologic signs of reactive bony changes associated with the tumour presented at the highest mean duration of all bony effects. Bony expansion and cortical destruction were statistically correlated with lesion duration. Tooth impaction was more common in children. Some mandibular lesions reached a significant size, resulting in impingement of the maxillary sinus, zygoma, orbit and pterygoid plates.

CONCLUSION

Due to unfortunate healthcare access constraints, ABs grow to significant sizes and exhibit features not often reported in the literature. The findings of this analysis highlighted the radiologic features of ABs expressed through the mean age and duration of the lesion. This emphasises the significance of timely management of these lesions.

LRP5, SLC6A3, and SOX10 Expression in Conventional Ameloblastoma

Cell proliferation and invasion are characteristic of many tumors, including ameloblastoma, and are important features to target in possible future therapeutic applications.

OBJECTIVE

The objective of this study was the identification of key genes and inhibitory drugs related to the cell proliferation and invasion of ameloblastoma using bioinformatic analysis.

METHODS

The H10KA_07_38 gene profile database was analyzed by Rstudio and ShinyGO Gene Ontology enrichment. String, Cytoscape-MCODE, and Kaplan-Meier plots were generated, which were subsequently validated by RT-qPCR relative expression and immunoexpression analyses. To propose specific inhibitory drugs, a bioinformatic search using Drug Gene Budger and DrugBank was performed.

RESULTS

A total of 204 significantly upregulated genes were identified. Gene ontology enrichment analysis identified four pathways related to cell proliferation and cell invasion. A total of 37 genes were involved in these pathways, and 11 genes showed an MCODE score of ≥0.4; however, only SLC6A3, SOX10, and LRP5 were negatively associated with overall survival (HR = 1.49 (p = 0.0072), HR = 1.55 (p = 0.0018), and HR = 1.38 (p = 0.025), respectively). The RT-qPCR results confirmed the significant differences in expression, with overexpression of >2 for SLC6A3 and SOX10. The immunoexpression analysis indicated positive LRP5 and SLC6A3 expression. The inhibitory drugs bioinformatically obtained for the above three genes were parthenolide and vorinostat.

CONCLUSIONS

We identify LRP5, SLC6A3, and SOX10 as potentially important genes related to cell proliferation and invasion in the pathogenesis of ameloblastomas, along with both parthenolide and vorinostat as inhibitory drugs that could be further investigated for the development of novel therapeutic approaches against ameloblastoma.

A Comparative Evaluation of Collagen in Ameloblastoma and Oral Squamous Cell Carcinoma using Picrosirius Red Staining with Polarizing Microscopy and CD44v6 Immunoreactivity

Background

Solid multicystic ameloblastoma (SMA) is a locally aggressive, benign odontogenic tumor of odontogenic origin with greater rate of recurrence. Epithelial-mesenchymal interaction plays an important role in tooth morphogenesis that shows complete differentiation of epithelial and ectomesenchymal components to the level of tooth formation. Tumor stroma in ameloblastoma is normal mature collagen that prevents differentiation to the level of tooth formation. Current study evaluates the role of stromal elements in aggressive behavior of SMA using picrosirius red staining with polarizing microscopy and CD44v6 immunohistochemistry (IHC).

Objectives

To compare nature of collagen using picrosirius red staining under polarized microscope and IHC expression of CD44v6 marker in SMA and oral squamous cell carcinoma (OSCC).

Methods

Thirty blocks were retrieved from departmental archives and subjected to picrosirius red staining and CD44v6 IHC staining. Slides stained with picrosirius red were observed under polarized microscope to report the birefringence pattern. IHC slides were annotated for intensity of staining of tumor cells.

Results

In contrast to OSCC's 40% red, 40% yellowish-red, and 20% greenish-yellow birefringence, SMA displayed 87% red, 13% yellowish-red, and 0% greenish-yellow. Compared to OSCC, which had tumor cells stained 9% strongly, 64% moderately, 27% mildly, and 0% negatively, SMA revealed 0% strong, 10% moderate, 60% weak, and 30% negative staining.

Conclusion

As opposed to OSCC, which exhibited a greater quantity of greenish-yellow birefringence of immature collagen, SMA showed predominantly red birefringence, which is suggestive of mature collagen with a lack of metastasis. Comparing SMA to OSCC, the lack of significant CD44v6 positivity suggests that there has not been perineural invasion or regional metastases in SMA.

Immunoexpression of stem cell markers SOX-2, NANOG AND OCT4 in ameloblastoma

Background

Ameloblastoma (AME) is characterized by a locally invasive growth pattern. In an attempt to justify the aggressiveness of neoplasms, the investigation of the role of stem cells has gained prominence. The SOX-2, NANOG and OCT4 proteins are important stem cell biomarkers.

Methodology

To verify the expression of these proteins in tissue samples of AME, dentigerous cyst (DC) and dental follicle (DF), immunohistochemistry was performed and indirect immunofluorescence were performed on the human AME (AME-hTERT) cell line.

Results

Revealed expression of SOX-2, NANOG and OCT4 in the tissue samples and AME-hTERT lineage. Greater immunostaining of the studied proteins was observed in AME compared to DC and DF (p < 0.001).

Conclusions

The presence of biomarkers indicates a probable role of stem cells in the genesis and progression of AME.

Comparative evaluation and Immunohistochemical expression of Syndecan-1 in Ameloblastoma and Dentigerous cyst

Background: Syndecans are type-1 heparan sulphate proteoglycans which play significant role in cell-cell and cell-extracellular matrix interaction. Syndecans are involved in tooth development and differentiation of mesenchymal cells. Amongst odontogenic lesions, ameloblastomas and dentigerous cysts are routinely encountered lesions with difference in treatment modality based on its aggressiveness. The objective of the present research was to study and compare immunohistochemical expression of syndecan-1 in ameloblastoma and dentigerous cyst. Method:  40 retrospectively diagnosed cases of ameloblastomas and dentigerous cysts were immunohistochemically stained against syndecan-1. The intensity of immunostaining and percentage of positive cells was assessed by three independent blind observers. Weighted kappa test was used to find out inter-observer reliability. Comparative evaluation of syndecan-1 expression between the two lesions was done using student t-test. Results:  There was statistically significant difference between the mean of score for intensity, mean of score for percentage of positive cells and total mean score of syndecan-1 between ameloblastoma and dentigerous cyst. Conclusion: Syndecan-1 may be involved in aetiopathogenesis of odontogenic lesions like ameloblastoma and dentigerous cyst. Also, weak expression in ameloblastoma indicates that tumor invasion and aggressiveness is related to cell adhesion molecule like syndecan-1.

Ameloblastoma in a Three-Year-Old Child with Hurler Syndrome (Mucopolysaccharidosis Type I)

Mucopolysaccharidoses (MPS) are a family of genetic diseases associated with a deficiency of alpha-L iduronidase, which causes a lack of catabolism of glycosaminoglycans (GAGs). Therefore, the accumulation of GAGs determines a wide spectrum of symptoms, typically found in a few syndromes like Hurler syndrome (HS). Among other specific manifestations, craniofacial abnormalities are crucial for the characterization of this syndrome. Ameloblastoma is a rare, benign, slow-growing, odontogenic tumor usually located in the mandible. Clear risk factors for the development of ameloblastoma remain unknown, but black patients have a fivefold increased risk. Clinically, it is characterized by a painless, variable-sized jaw swelling. Although classified as a benign tumor, ameloblastoma often has a severe clinical outcome. The most common type of ameloblastoma is the solid/multicystic/conventional one. A computed tomography scan (CT) with and without contrast is the gold standard for evaluating this kind of neoplasia. Conservative or radical surgery is the mainstay of treatment. In this case report, we described an unusual clinical assessment of conventional ameloblastoma interesting the posterior left mandible of a 35-month-old child affected by HS. This case represented a suggestive challenge both from a diagnostic and a therapeutic point of view. The patient was disease-free at 2 years’ follow-up.

Assessment of Tumor Angiogenesis by Expression of CD 105 in Ameloblastoma, Odontogenic Keratocyst and Central Giant Cell Lesion

Background:

Angiogenesis is critical for tumor growth and reflects the aggressive behavior of invasive odontogenic lesions [like amelogenesis (AM) (AM), Odontogenic Keratocyst (OKC) and Central giant cell lesion (CGCL)]. Mean vascular density (MVD) shows the angiogenic potential and CD105 is an ideal endothelial biomarker due to its specificity to new blood vessels for MVD detection. The aim of the study was to compare the MVD (angiogenic potential) among AM, OKC and CGCL in comparison to Pyogenic Granuloma (PG) using CD105 biomarker.

Methods:

Sixty-four primary cases of odontogenic invasive tumors (AM, OKC and CGCL) and PG, diagnosed clinically and histologically were included in the study, with 16 samples in each group. Tissue samples of peripheral AM, Peripheral GCL of jaws, malignant AM, and specimen with insufficient tissue were excluded. Tissue sections were embedded, processed and stained using Hematoxylin and Eosin (H and E). Immunohistochemistry was performed using antibodies against CD105, with positive brown cytoplasmic staining in the endothelial cells of neo-vasculature. Distinct countable, positively stained endothelial cell or clusters were evaluated under light microscope for identification of MVD. ANOVA and t-test were applied for statistical analysis of data.

Results:

Highest MVD was displayed in CGCL (32.99±0.77) and the minimum was observed in OKC (7.21± 0.75) respectively. CGCL showed significantly higher MVD to AM, OKC and PG lesions (p<0.05). AM (8.07± 0.36) and Odontogenic Keratocyst (7.21± 0.75) showed comparable MVD, which was lower than PG (14.7± 0.96) and CGCL vascular density (p < 0.01) respectively.

Conclusion:

CGCL was most aggressive, with highest MVD among the investigated odontogenic lesions (OKC, AM and PG). The proliferative aggressive behavior of Odontogenic Keratocyst is comparable to AM due to comparable mean vascular density.

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.

A Novel lncRNA ENST00000512916 Facilitates Cell Proliferation, Migration and Cell Cycle Progression in Ameloblastoma

Objective

Our purpose was to identify up-regulated long noncoding RNA ENST00000512916 in ameloblastoma (AB) and explore its role in the progression of AB.

Methods

We analyzed lncRNA microarray expression profile between six paired AB and normal oral mucosa (NOM) tissues. An up-regulated lncRNA, ENST00000512916 was identified and validated by real-time qPCR. Cell proliferation, migration and cell cycle were detected by CCK-8 assay, transwell chamber and flow cytometry, respectively. Western blotting analysis was used to measure the expression of cell-cycle-related proteins including CyclinD1 and Cyclin-dependent kinase (CDK) 2/4/6. In addition, Xenograft tumor model was constructed to investigate tumor growth.

Results

Real-time qPCR confirmed that lncRNA ENST00000512916 was up-regulated in AB tissues. ENST00000512916 knockdown significantly inhibited cell proliferation, migration and the expression of CDK2/4/6 in AM-1 cells. Moreover, ENST00000512916 knockdown suppressed tumor growth in vivo. We also found that ENST00000512916 overexpression significantly promoted the expression of HOXC13 in AM-1 cells. Overexpression of ENST00000512916 promoted cell cycle progression in AM-1 cells, which was reversed by HOXC13 knockdown.

Conclusion

Our findings reveal that lncRNA ENST00000512916 promotes cell proliferation, migration and cell cycle progression of AB.

Expression of CD34, VEGFR3 and eosinophil density in selected odontogenic tumors- a pilot study

Background

Limited statistically and clinically significant studies have been down on connective tissue factors in the odontogenic tumors. Therefore, the aim of this study was to determine the biological behavior of two selected epithelial odontogenic tumors (Ameloblastoma and Adenomatoid odontogenic tumor) by detecting CD34, VEGFR3 and eosinophil densities.

Methods

In this cross-sectional study, paraffin blocks including 20 cases of ameloblastoma and 20 (AOT), were selected. Totally, 4 sections were prepared for hematoxylin-eosin, Congo red staining, immunohistochemistry with CD34 and VEGFR3. Expression of VEGFR3, CD34 and lymphatic, blood vessels and eosinophil densities was examined.

Results

The mean of blood, lymphatic vessels and eosinophils densities in ameloblastoma were 14.9 ± 6.4, 4.4 ± 2 and 3.2 ± 2.7, respectively; and in AOT, they were 8.9 ± 3.4, 3.6 ± 1.3 and 1.2 ± 07, respectively. There was a significant difference in eosinophils and blood vessels densities between the two lesions (p = 0.005; p = 0.003). By increasing the density of eosinophils, the density of the blood vessels increased in both lesions (r = 0.539, P = 0.001) There was no positive relationship between eosinophils and lymphatic vessels densities in the two above mentioned odontogenic lesions (p = 0.288, R = 0.191).

Conclusion

It can be suggested that tumor angiogenesis and eosinophil densities may play a more effective role than lymphangiogenesis in local invasive behavior of ameloblastoma rather than AOT.

Shark tooth regeneration reveals common stem cell characters in both human rested lamina and ameloblastoma

The human dentition is a typical diphyodont mammalian system with tooth replacement of most positions. However, after dental replacement and sequential molar development, the dental lamina undergoes apoptosis and fragments, leaving scattered epithelial units (dental lamina rests; DLRs). DLRs in adult humans are considered inactive epithelia, thought to possess limited capacity for further regeneration. However, we show that these tissues contain a small proportion of proliferating cells (assessed by both Ki67 and PCNA) but also express a number of common dental stem cell markers (Sox2, Bmi1, β-catenin and PH3) similar to that observed in many vertebrates that actively, and continuously regenerate their dentition. We compared these human tissues with the dental lamina of sharks that regenerate their dentition throughout life, providing evidence that human tissues have the capacity for further and undocumented regeneration. We also assessed cases of human ameloblastoma to characterise further the proliferative signature of dental lamina rests. Ameloblastomas are assumed to derive from aberrant lamina rests that undergo changes, which are not well understood, to form a benign tumour. We suggest that dental lamina rests can offer a potential source of important dental stem cells for future dental regenerative therapy. The combined developmental genetic data from the shark dental lamina and ameloblastoma may lead to the development of novel methods to utilise these rested populations of adult lamina stem cells for controlled tooth replacement in humans.

Adjunctive Strategies for Benign Maxillofacial Pathology

Benign cysts and neoplasms of the maxillofacial region can vary in behavior, with some growing rapidly and resulting in destruction of surrounding structures. Despite their benign histology, many require often-morbid treatment to prevent recurrence of these lesions. Several less invasive and adjunctive medical treatments have been developed to lessen the morbidity of surgical treatment. As the molecular and genomic pathogenesis of these lesions is better understood, more directed treatments may lessen the burden for patients.

Calretinin expression in odontogenic cysts and odontogenic tumors and the possible role of calretinin in pathogenesis of ameloblastoma

Introduction:

Histopathological diagnosis of odontogenic cysts and tumors is a task mostly accomplished with hematoxylin and eosin staining. However, the use of additional diagnostic modalities such as immunohistochemistry may be necessary in histologically similar lesions. The reports of studies which have used calretinin as an immunohistochemical marker for ameloblastoma have been conflicting.

Aim:

The aim of the study was to evaluate the use of calretinin as a specific diagnostic marker for ameloblastoma and observe its expression in odontogenic cysts and other odontogenic tumors.

Materials and Methods:

Formalin-fixed, paraffin-embedded sections were taken from the archives which included 15 cases each of dentigerous cyst, radicular cyst, odontogenic keratocyst and ameloblastoma five cases of adenomatoid odontogenic tumor and three cases of ameloblastic carcinoma. Immunohistochemistry was done with calretinin antibody.

Results:

All ameloblastomas were positive for calretinin, whereas no other tumor or cyst showed positivity. Differences in proportion of calretinin expression were statistically significant with P = 0.000.

Conclusion:

Calretinin can be considered as a specific marker for ameloblastomas.

Hemangiomatous ameloblastoma: Case report with a brief review

Ameloblastoma is a benign epithelial odontogenic tumor with many histological variants. Hemangiomatous ameloblastoma (HA) is a very rare variant which shows unique histopathological features varying from conventional ameloblastoma. We present a case of a 35-year-old female patient with a swelling over right lower back region of jaw, showing mixed radiolucent-opacity. Incisional biopsy showed microscopic features of desmoplastic ameloblastoma showing extensive desmoplasia and compressed odontogenic epithelial islands. Excisional biopsy revealed ameloblastomatous areas with extensive vascular component microscopically. Based on these findings, a diagnosis of HA was made.

Analysis of Prevalence and Clinical Features of Ameloblastoma and its Histopathological Subtypes in Southeast Myanmar and Lower Northern Thailand Populations: A 13-Year Retrospective Study

INTRODUCTION

Prevalence of ameloblastomas has been established worldwide but collective data of ameloblastoma in Southeast Asian countries has not been well analyzed.

AIM

Aim of this study was to report analysis and comparison of the prevalence and demographic data of clinical features of ameloblastoma and its histopathological variants in Southeast Myanmar and lower Northern Thailand populations.

MATERIALS AND METHODS

A retrospective study on ameloblastoma was performed based on the availability of oral biopsy specimens in Faculty of Dentistry, Naresuan University, Phitsanulok, Thailand, between January 2002 and August 2015. The collected data were subjected to descriptive statistical analyses with the SPSS version 17.0 statistical software package (SPSS Inc., Chicago, USA). Pearson's chi square (χ2) test and t-test were employed. The critical level of significance was set at p<0.05.

RESULTS

Total of 616 cases were reviewed, 30 cases (5%) were diagnosed as ameloblastoma with male:female ratio of 1.14:1. The mean age of the patients was 31.3±15.6 years. The predominance anatomical distribution was observed in the mandible (86.7%). Posterior body-ramus-angle region was the most common site. Almost all cases were asyptomatic and most common clinical manifestation was swelling of affected region. Multilocular radiolucency was observed in 70% of cases, whereas 30% were unilocular. Three subtypes of ameloblastomas were diagnosed: unicystic ameloblastoma (20%), conventional solid/multicystic ameloblastoma (70%), and desmoplastic ameloblastoma (10%). The most common histologic pattern was the plexiform type (57.2%) followed by follicular type (23.8%).

CONCLUSION

Prevalence of ameloblastoma in Southeast Myanmar and lower Northern Thailand populations correspond with data from other geographic areas of Thailand and other Asian countries. However, some demographic and histopathological profiles are different, with plexiform ameloblastoma being the most common subtype in this study.

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.

The regulation of bone turnover in ameloblastoma using an organotypic in vitro co-culture model

Ameloblastoma is a rare, odontogenic neoplasm with benign histopathology, but extensive, local infiltrative capacity through the bone tissue it originates in. While the mechanisms of ameloblastoma invasion through the bone and bone absorption are largely unknown, recent investigations have indicated a role of the osteoprotegerin/receptor activator of nuclear factor kappa-B ligand regulatory mechanisms. Here, we present results obtained using a novel in vitro organotypic tumour model, which we have developed using tissue engineering techniques. Using this model, we analysed the expression of genes involved in bone turnover and detected a 700-fold increase in receptor activator of nuclear factor kappa-B ligand levels in the co-culture models with ameloblastoma cells cultured with bone cells. The model described here can be used for gene expression studies, as a basis for drug testing or for a more tailored platform for testing of the behaviour of different ameloblastoma tumours in vitro.

Molecular and genetic aspects in the etiopathogenesis of ameloblastoma: An update

Ameloblastoma is the second most common benign epithelial odontogenic tumor and though it is of a benign nature, it is locally invasive, has a high recurrence rate and could potentially become malignant. Many theories have been proposed to explain the pathogenesis of ameloblastoma. Proper understanding of the pathogenic mechanism involved in ameloblastoma and its proliferation aids in constituting proper treatment of choice at an early stage, preventing morbidity associated with extensive therapy. An attempt has been made to discuss the current concepts related to molecular and genetic changes that occur in ameloblastoma as these could affect treatment plan and prognosis.

Immunohistochemical Detection of p75 Neurotrophin Receptor (p75-NTR) in Follicular and Plexiform Ameloblastoma

INTRODUCTION

Ameloblastoma holds a unique position among benign tumours by its locally destructive and invasive nature. Recently improvised molecular techniques helped researchers to unravel the myth behind such biologic behaviour. Though interesting findings have been delivered, the rhythmic correlation regarding the exact mechanism still remains lacking. Neurotrophins and their receptor mediated pathways play a crucial role in survival, death and differentiation of many neuroectoderm derived cells. With this background, the study has been aimed to investigate the expression of p75-NTR (Neurotrophin Receptor) in follicular and plexiform ameloblastoma.

AIM

To analyze the immunohistochemical expression pattern of p75-NTR in ameloblastoma and to compare the immunohistochemical expression pattern of p75-NTR among the histological types of ameloblastoma, follicular and plexiform patterns.

MATERIALS AND METHODS

Total 22 ameloblastomas (12 follicular, 10 plexiform) were immuno-stained with anti-human p75-NTR mouse IgG monoclonal antibody and the pattern of staining is statistically analyzed.

RESULTS

Only 11 (10 follicular, 1 plexiform) out of 22 ameloblastomas showed immuno-reactivity to p75-NTR. In ameloblastoma, only the peripheral pre-ameloblast like tall columnar cells showed reactivity whereas the stellate reticulum-like cells were immuno-negative. The staining pattern was membranous in the immuno-reactive cells. The results were studied with the downstream pathways from the literature and a possible mechanism has been proposed.

CONCLUSION

The expression pattern of p75-NTR was found to be more in follicular ameloblastoma than plexiform.

Sonic Hedgehog Signalling Pathway and Ameloblastoma - A Review

Ameloblastoma is a benign but aggressive odontogenic neoplasm arising from odontogenic epithelium. Many theories have been proposed to explain the pathogenesis of ameloblatoma. Numerous signalling pathways have been implicated to be associated in the development and progression of this neoplasm. Studies have found association of various signalling molecules of Sonic Hedgehog Pathway, namely SHH, PTCH1, SMO, Gli 1, Gli 2, Gli 3, with ameloblastoma. Knowledge about this pathway will help us to understand the nature and behaviour of this neoplasm. This will open the door towards new treatment modalities.

Gnathic and peripheral ameloblastomas lack human papillomavirus DNA

Human papillomavirus (HPV) has been associated with a variety of head and neck neoplasms, including squamous cell carcinomas and Schneiderian papillomas. Ameloblastomas can arise from either the gnathic bones or peripheral soft tissues. Peripheral sinonasal ameloblastomas share clinical features with Schneiderian papillomas. A small number of reports have described detection of HPV DNA within ameloblastomas. However, Most of these cases was reported in the 1990s, used the polymerase chain reaction technique, and only examined gnathic tumors. The current study was designed to determine whether low- or high-risk HPV DNA could be detected in gnathic or peripheral ameloblastomas using in situ hybridization. Twenty-nine examples of gnathic osseous and peripheral head and neck ameloblastomas were obtained from the authors' archives (University of Virginia and the Johns Hopkins Hospital). High-risk HPV DNA was not detected in any of the 29 tumors analyzed. Low-risk HPV DNA was identified in only 1 tumor, which was peripheral in origin, and from an immunocompromised patient. We believe that the HPV in this case represents a background "passenger" infection. This study demonstrates that HPV of either high- or low-risk subtypes is unlikely to play a role in the pathogenesis of sinonasal ameloblastomas.

ESEM Detection of Foreign Metallic Particles inside Ameloblastomatous Cells

Ameloblastoma is a borderline tumor of odontogenic origin, with a high recurrence rate and possible local aggressiveness. The etiopathogenetic factors involved in its occurrence are not still defined and our study has been precisely aimed to search for novel factors associated with its development. Sections cut from paraffin blocks, containing the representative specimens of 18 different ameloblastomas, collected in a 15-year period (1999-2014), have been observed by an environmental scanning electron microscope, in order to search micro- and nano-sized particles and to identify their composition. In all the neoplastic cases, micro- and nano-sized metallic debris, differing in size and composition, have been detected inside the ameloblastomatous cells. On the contrary, the total absence of metallic particles in the healthy control cases has been emerged. Our results reveal a relationship between ameloblastoma and metallic particulate. The cigarette smoke and the routine dental practice appear the most probable source for the presence of these biopersistant inorganic particles inside the neoplastic cells.

A discussion of some advancements and some persistent difficulties in the recognition and understanding of the histopathologic and molecular features of selected odontogenic tumors and tumor-like malformations

Overgrowths of epithelial, ectomesenchymal, and/or mesenchymal elements of the tooth-forming apparatus are quite variable with respect to their histopathologic characteristics and biological behaviors. Investigations of a variety of odontogenic lesions have led to an enhanced comprehension of many salient diagnostic features. This discussion provides an update with respect to the understanding of odontogenic tumors and tumor-like malformations and attempts to assist pathologists in the recognition and classification of these lesions.

Immunohistochemical expression of Survivin and its relationship with cell apoptosis and proliferation in ameloblastomas

Ameloblastoma behavior is related to the potential of tumor cells to inhibit apoptosis and to initiate a proliferative phase. This study was performed to compare the immunoexpression of Survivin with Bcl-2, Bax, and Ki-67 and to associate them with the histopathological type of each variant of ameloblastoma.

MATERIAL AND METHODS

Using the World Health Organization (WHO) criteria for ameloblastoma, 110 cases were selected. The cases were classified as solid/multicystic and unicystic ameloblastomas. Cellular counts of cytoplasmic immunoexpression were assessed for cytoplasmic Survivin, Bcl-2, and Bax, while the nuclear immunoexpression of Survivin and Ki-67 was assessed using label index.

RESULTS

Cytoplasmic Survivin and Bcl-2 showed higher percentages of immunoexpression in solid multicystic ameloblastomas compared to unicystic ameloblastomas (P < 0.05). Bax, Ki-67, and nuclear Survivin were expressed in higher percentages in unicystic ameloblastomas.

CONCLUSIONS

Cytoplasmic Survivin and Bcl-2 immunoexpression levels were elevated in relation to Bax immunoexpression, suggesting aggressive ameloblastoma behavior, while Ki-67 and nuclear Survivin immunoexpression may be associated with the type of tumor morphology that influences cellular counts or with the greater capacity for cellular proliferation and tumor growth.

The diagnostic usefulness of immunohistochemistry for odontogenic lesions

The diagnosis of odontogenic tumors can be challenging, largely due to their rarity and consequent difficulties in gaining experience in their assessment. In most cases, careful attention to morphology, in conjunction with clinical and radiological features will allow a diagnosis to be made. However, in some cases, immunohistochemical analysis of the tumor may be useful. In this review we will outline the immunohistochemical expression profile of normal developing odontogenic tissues and a range of odontogenic tumors. In many cases the immunohistochemical markers are neither specific nor sensitive enough to be of help in diagnosis, but in some cases such analysis may prove very useful. Thus we have outlined a limited number of circumstances where immunohistochemistry may be of use to the practicing diagnostic pathologist.

An overview of molecular and genetic alterations in selected benign odontogenic disorders

CONTEXT

Some dental abnormalities have environmental causes. Other odontogenic alterations are idiopathic and may have hereditary etiologies. Investigations of these conditions are ongoing.

OBJECTIVE

To provide a discussion of developmental odontogenic abnormalities and benign odontogenic overgrowths and neoplasms for which genetic alterations have been well demonstrated and well documented.

DATA SOURCES

Relevant peer-reviewed literature.

CONCLUSIONS

The understanding of benign odontogenic lesions at a molecular level is rather well developed for some lesions and at the initial stages for many others. Further characterization of the molecular underpinnings of these and other odontogenic lesions would result in an enhanced comprehension of odontogenesis and the pathogenesis of a variety of odontogenic aberrations. These advancements may lead to better prevention and treatment paradigms and improved patient outcomes.

Giant ameloblastoma mortality; a consequence of ignorance, poverty and fear

Ameloblastoma is a benign tumour of odontogenic origin. Although locally invasive, delay in treatment can lead to severe disfiguring of the facial region. In this report, we present two cases, a man and a woman, of a large ameloblastoma that presented with the typical radiographic features of variably sized radiolucent loculations. Patients presented initially with relatively small tumours but due to fear of surgery, ignorance and possibly poverty, tumour growth became enormous. The female patient died while awaiting consent for surgery and the male patient died at home due to complications closely associated with fear and growth of tumour. Literatures on mortality of ameloblastoma are reviewed. The need for more public enlightenment on the nature and treatment of facial tumours is highlighted.

Expression of human papillomavirus is correlated with Ki-67 and COX-2 expressions in keratocystic odontogenic tumor

The aim of the current study was to investigate the presence of human papillomavirus (HPV) and evaluate its association with Ki-67 and cyclooxygenase-2 (COX-2) expressions in keratocystic odontogenic tumor (KCOT). Nineteen cases were included in the present study. Conventional PCR method and immunohistochemical analysis were performed for the detection of HPV-DNA and HPV-L1 capsid protein. Moreover, the expressions of Ki-67 and COX-2 proteins were analyzed immunohistochemically. HPV-DNA was detected in 36.8% (7/19) of tumor samples, whilst HPV-L1 protein was identified in 68.4% (13/19) of them. The Kappa coefficient statistical test showed a moderate agreement (κ 0.424) between PCR and IHC assays for HPV detection. Expression of HPV-DNA was positively correlated with Ki-67 and COX-2 expressions (p < 0.05), whereas HPV-L1 positive staining was positively correlated with COX-2 (p < 0.05) and highly associated with those of Ki-67 (p < 0.01). There was no significant correlation between the presence of HPV and the recurrence of the studied lesions. The results of the current study showed that active HPV infection was present in the odontogenic epithelium of KCOT, and it was associated with increased proliferation rate and COX-2 expression. These findings suggest that HPV may have a role in the pathogenesis and aggressiveness of KCOT. Based on these conclusions, we recommend further investigations of HPV vaccine or antiviral therapy and COX-2 inhibitors as nonsurgical options in the prevention and management of KCOT.

Progress towards personalized medicine for ameloblastoma

Ameloblastoma is a locally infiltrative benign odontogenic neoplasm. Tumours may be large, destructive and recurrent, requiring radical surgery with associated facial deformity and morbidity. The molecular pathogenesis of this tumour has been unclear, retarding the development of non-invasive gene-targeted therapies. In a recent paper in this journal, Kurppa et al. [4] showed that EGFR-targeted therapy blocked cell proliferation in an ameloblastoma primary cell culture. That this therapy was not effective in another primary cell culture led to the discovery of the oncogenic BRAF V600E mutation in a high proportion (63%) of ameloblastoma samples. By defining two separate pathways, both of which can be specifically targeted, these findings are an important step towards personalized medicine of ameloblastoma. We discuss the findings in the broader context of ameloblastoma, as well as the effects of tumour microenvironment and molecular heterogeneity that need to be taken into account when considering the use of personalized therapies based on specific genetic mutations in individual patients.

R, Roa K. UD, Joshua E, Ahmed AS, Chittamsetty H. Immunohistochemical Expression of PCNA in Epithelial Linings of Selected Odontogenic Lesions

AIM

Though odontogenic lesions have in common origin from the primitive odontogenic epithelium , there is a diversity in their initiation behavior and growth. The aggressive nature of odontogenic keratocyst similar to ameloblastoma in comparision with the other common odontogenic (dentigerous and radicular) cyst could be due to possible differences in their epithelial linings. PCNA (Proliferating cell nuclear antigen) is a cell cycle related antigen, used in the study of cell kinetics of these epithelial linings, to corelate the biological behaviour among these common odontogenic lesions.

OBJECTIVES

This paper has intended to study the cell kinetics of 4 selected odontogenic lesions (dentigerous cyst, radicular cyst,odontogenic keratocyst and ameloblastoma) to demonstrate differences in their epithelial linings.

MATERIAL AND METHODS

Sixty samples of paraffin embedded tissue specimens (archival tissues) were included (15 radicularcysts, 15 odontogenic keratocysts; 15 dentigerous cysts and15 Ameloblastoma.

RESULTS

Among cyst OKC had higher values than DC and RC. When staining results of all the cyst were compared individually with ameloblastoma ,the staining results of OKC was similar to ameloblastoma ,and ameloblastoma presented higher values than OKC (p=0.000).

CONCLUSION

The results of this study show 1) Though OKC and DC are developmental in origin and radicular cyst is inflammatory, OKC has intrinsic growth potential among these cyst 2). Ameloblastoma has similar proliferative potential as OKC and hence it has been reinforced as KCOT(Keratocystic odontogenic tumour) in the recent classification.

Unicystic Ameloblastoma Masquerading as Huge Periapical Lesion, both Clinically and Histopathologically: Two Case Reports with Review of Literature

Unicystic ameloblastoma (UA) is one of the variants of ameloblastoma. It manifests as unilocular radiolucency in the mandible or maxilla on X-ray scans. In very rare cases, it can appear as a localized periradicular radiolucent area, imitating a periapical lesion. In this article, we present two cases of UA that were initially misdiagnosed as periapical lesions. Subsequently, surgical enucleation was performed and the diagnosis of UA was confirmed histopathologically.

Mandibular resection and reconstruction in the management of extensive ameloblastoma

PURPOSE

To present our experience with the management of 31 extensive mandibular ameloblastomas treated with segmental mandibulectomy, reconstruction with free fibula or iliac crest flap, and rehabilitation with immediate or delayed endosteal dental implants.

PATIENTS AND METHODS

The study sample comprised 31 patients with histologically confirmed mandibular ameloblastomas. Primary ameloblastomas were treated in 23 patients, and recurrent ameloblastomas affected 8 patients. Mandibular defect sizes ranged from 3.5 to 12.5 cm (mean, 5.6 cm). A free fibula osseous or osteocutaneous flap was used 17 times for reconstruction; in the remaining 14, a free iliac crest osseous or osteomuscular flap was chosen. Dental implants were positioned in 25 patients; implant procedures were performed simultaneously with reconstruction in 21 cases.

RESULTS

All flaps were transplanted successfully, and no major complication occurred postoperatively. Final histologic examinations showed 27 multicystic and 4 unicystic ameloblastomas. Free margins were achieved in all patients. The duration of follow-up was 18 to 120 months (mean, 53.6 months). No patient showed clinical or radiologic signs of recurrence. The dental implant success rate was 100%.

CONCLUSIONS

Segmental mandibular resection followed by immediate defect reconstruction with bone-containing free flaps with immediate dental implant placement should be considered as the treatment of choice for extensive mandibular ameloblastomas.

Epigenetic regulation of matrix metalloproteinase expression in ameloblastoma

BACKGROUND

An ameloblastoma is a benign odontogenic neoplasm with aggressive behaviour and high recurrence rates. The increased expression of matrix metalloproteinases (MMPs) has been reported in ameloblastomas. In the present study, we hypothesised that epigenetic alterations may regulate MMP expression in ameloblastomas.

METHODS

We investigated the methylation status of the genes MMP-2 and MMP-9 in addition to mRNA transcription and protein expression in ameloblastomas. Methylation analysis was performed by both methylation-specific polymerase chain reaction (MSP-PCR) and restriction enzyme digestion to evaluate the methylation profile of MMP-2 and MMP-9 in 12 ameloblastoma samples and 12 healthy gingiva fragments, which were included as controls. Furthermore, we investigated the transcription levels of the genes by quantitative reverse-transcription PCR (qRT-PCR). Zymography was performed to verify protein expression in ameloblastomas.

RESULTS

The ameloblastomas showed a high frequency of unmethylated MMP-2 and MMP-9, whereas the healthy gingival samples presented a sharp prevalence of methylated MMPs. Higher expression levels of MMP-9 were found in ameloblastomas compared to healthy gingiva. However, no significant differences in the MMP-2 mRNA expression between groups was found. All ameloblastomas showed positive expression of MMP-2 and MMP-9 proteins.

CONCLUSIONS

Our findings suggest that expression of MMP-9 is increased in ameloblastomas and is possibly modulated by unmethylation of the gene.

Giant ameloblastoma

Ameloblastoma is the most frequent of the odontogenic tumors. We report a case of a giant ameloblastoma involving the maxillary region and describe its ultrasonography and computed tomography findings.

Loss of heterozygosity (LOH) in tumour suppressor genes in benign and malignant mixed odontogenic tumours

Although molecular alterations are reported in different types of odontogenic tumours, their pathogenesis remains to be established. Loss of heterozygosity (LOH) studies allow the identification of minimal regions of deletions of known or putative tumour suppressor genes, the losses of which may promote neoplastic growth. The purpose of this study was to investigate LOH in a set of odontogenic mixed tumours. Tumour suppressor gene loci on 3p, 9p, 11p, 11q and 17p chromosomes were analysed in five samples of ameloblastic fibroma (AF), three samples of ameloblastic fibro-odontoma (AFO) and three samples of ameloblastic fibrosarcoma (AFS). The most frequently lost genetic loci were p53 (17p13, 62%) and CHRNB1 (17p13, 55%). LOH at the chromosome regions 3p24.3, 9p22 and 9p22-p21 was identified only in AFS. No sample showed LOH at the chromosomal loci 3p21.2 and 11q13.4. For the region 9p22-p13, LOH occurred in one sample of AFO. The fractional allelic loss (FAL) was calculated for each sample. The mean FAL of the benign lesions (i.e. AF and AFO) was 22%, whereas the mean FAL of the malignant lesions (i.e. AFS) was 74.6%. In conclusion, our results show a higher FAL in AFS compared to its benign counterparts and reveal a different pattern of LOH of tumour suppressor genes in AFS, which may regulate changes in tumour behaviour.