Benign epithelial odontogenic tumors

Teeth are formed from a complex interaction of primitive ectoderm and ectomesenchymal tissues. Because humans develop 2 sets of teeth (deciduous and permanent), odontogenesis is a prolonged biologic process. Residues of odontogenic tissues are present in most humans- both during and after odontogenesis. These elements may be found in either bone or soft tissue of the jaws and may contribute to the formation of odontogenic tumors in these sites. Further, the mixture of epithelium and mesenchyme necessary for tooth formation allows for the development of tumors composed of either element or for mixed neoplasms. This article discusses 4 of the 5 benign odontogenic neoplasms that are of epithelial origin and offers an agreed on classification scheme, which includes important clinicopathological subtypes. Specifically discussed are ameloblastoma, calcifying epithelial odontogenic tumor (Pindborg tumor), adenomatoid odontogenic tumor, and squamous odontogenic tumor. A brief history of each tumor is given along with a discussion of demographic data, clinical findings, radiographic features, and gross features where useful. A thorough discussion is presented of diagnostic histopathology including histologic variants. Generally accepted modes of therapy and follow-up recommendations are discussed.     

Benign epithelial odontogenic tumors

The group of benign epithelial odontogenic tumors consists of the four member types of the ameloblastoma family (solid/multicystic, extraosseous/peripheral, desmoplastic, unicystic), squamous odontogenic tumors, calcifying odontogenic tumors, adenomatoid odontogenic tumors, and keratocystic odontogenic tumors, the former "keratocysts" that were recently reclassified by the World Health Organization and are now regarded as tumors. The latter are by far the most frequent tumors in this group, followed by solid/multicystic ameloblastoma. Although the etiology of these lesions is still unknown, a close relationship to normal tooth development is obvious, which is partially imitated by some tumors. Despite some similarities to each other, at least in part, the biological behavior of these lesions is quite different, as are treatment modalities. The diagnosis is essentially based on localization (intraosseous vs. extraosseous/peripheral) and histology, whereupon the correlation of histological findings with radiographic morphology may be of additional diagnostic value. Because of the range of variation, immunohistochemical investigations are not helpful in diagnosing a particular case.     

Malignant epithelial odontogenic tumors

Malignant epithelial odontogenic tumors are very rare. They may arise from the epithelial components of the odontogenic apparatus. The rests of Malassez, the reduced enamel epithelium surrounding the crown of an impacted tooth, the rests of Serres in the gingiva, and the linings of odontogenic cysts represent the precursor cells for malignant transformation. Because metastatic carcinoma is the most common malignancy of the jaws, the diagnosis of a primary intraosseous carcinoma must always be made to the exclusion of metastatic disease. Odontogenic carcinomas include malignant (metastasizing) ameloblastoma, ameloblastic carcinoma, primary intraosseous squamous cell carcinoma, clear cell odontogenic carcinoma, and malignant epithelial ghost cell tumor. There are specific histopathologic features that support the diagnosis of a primary carcinoma of odontogenic epithelium which are presented in this article. Immunohistochemical (IHC) staining is important for distinguishing clear cell odontogenic carcinoma from metastatic renal cell tumors, yet IHC stains are not particularly helpful for other lesions in this group-all of which exhibit low molecular weight cytokeratin positivity. Aggressive growth and nodal and distant metastases occur with all of these entities.     

Benign mixed odontogenic tumors

As a group, the mixed odontogenic tumors histologically resemble various stages of tooth formation (odontogenesis). Because of this, confusion arises in diagnosis and nomenclature unless one is familiar with normal tooth development and its subsequent resemblance to the neoplasms and hamartomas which arise from the tooth-forming tissues of the jaws. This article reviews odontogenesis and relates it to the formation of the mixed odontogenic tumors-the ameloblastic fibroma, ameloblastic fibro-odontoma, and the odontomas. Correlation of clinical and radiographic features with the histologic features will generally result in correct diagnosis and proper treatment.     

Observations by G-banding in benign odontogenic tumors

The G-banding patterns in five cultured benign odontogenic tumors are described. Abnormal stem sideline karyotypes were observed in two tumors, whereas the remaining three tumors had a normal stemline. The latter cases, however, contained different types of variant cells, often showing deviations of nonrandom character. The results are discussed in relation to chromosomal findings in other benign tumor types and, briefly, in relation to oncogenes. A stepwise evolutionary pattern, which might be common to all benign tumor types, is suggested.     

Immunolocalisation of laminin-1 in keratocystic odontogenic tumors

Keratocystic odontogenic tumors (KOTs) are distinct odontogenic lesions frequently affecting the jawbones. They may be associated with nevoid basal cell carcinoma syndrome (NBCCS), and may exhibit disorders involving the extracellular matrix. The aim of this study was to investigate the immunolocalisation of laminin-1 in 20 cases of KOTs in order to contribute to the characterization of this protein, which is little studied in odontogenic tumors. Our results showed laminin-1 in all 20 KOTs studied; its labelling intensity was weak in three cases (15%), moderate in five (25%) and strong in 12 cases (60%). Laminin-1 immunolocalisation was predominantly continuous in 18 (90%) KOTs, including areas of acanthosis, subepithelial split and epithelial buds. Weak immunolabelling was observed in regions exhibiting an inflammatory process, especially in the case of intense inflammation. These findings suggest that laminin-1 does not participate in biological processes such as cystic epithelium-cystic wall separation or the formation of epithelial islands in KOTs. Furthermore, the discontinuous and weak labelling of this protein in the basement membrane of these tumors is probably a consequence of the inflammatory process in the tumor stroma.     

Odontogenic tumor with combined characteristics of adenomatoid odontogenic and calcifying epithelial odontogenic tumors

A very rare odontogenic epithelial tumor with the combined characteristics of an adenomatoid odontogenic tumor (AOT) and calcifying epithelial odontogenic tumor (CEOT) was found in a 27 year old female. The histopathology, immunohistochemistry of keratin, lectin-binding patterns and distribution of carbonic anhydrase were determined. The nature of the calcified bodies was also examined biophysically. The tumor consisted of cuboidal and columnar odontogenic epithelial cells in the cystic wall, and AOT and CEOT in the central cavity. Odontogenic epithelial cells forming the cyst wall in the CEOT were positive for TK- and KL1-keratins, while that detected with PKK1 antibody was absent in the tumorous epithelium. Lectin binding of tumor epithelial cells was examined with Concanavalin A (Con A), peanut agglutinin (PNA), soybean agglutinin (SBA), dolichos biflorus agglutinin (DBA), wheat germ agglutinin (WGA), ricinus communis agglutinin (RCA-I), and ulex europeus agglutinin I (UEA-I) lectins, and the tumor epithelium indicated existence of glucose, mannose, Gal, GalNAc, and GlcNAc residues. The lectin binding patterns of the calcified material showed an increased intensity by enzymatic pretreatments. With an electron probe X-ray microanalyser (EPMA), the calcified lesions gave a high peak for calcium ion and for phosphorus ion and a low one for magnesium ion, as obtained from line and surface analysis.     

Expression of p21RAS in odontogenic tumors.

Using an immunohistochemical assay 10 benign odontogenic tumors were evaluated for expression of the HRAS- and KRAS-encoded gene products p21RAS. Overexpression of p21RAS was found in ameloblastomas, ameloblastic fibromas and odontogenic myxomas compared with normal human developing teeth. The highest expression was noted in a recurrent plexiform ameloblastoma in which almost 100% of the tumor cells were brightly reactive. In general, p21RAS was preferentially expressed in ectodermal cells of odontogenic tumors, consistent with the findings in the tooth germs. The significance of p21RAS expression is considered in relation to the biological behavior of ameloblastomas.     

Gene mutation analysis and immunohistochemical study of beta-catenin in odontogenic tumors

In the present study the significance of nuclear/cytoplasmic expression of beta-catenin (CTNNB1) and mutation of the CTNNB1 gene (CTNNB1) in odontogenic tumors was examined. Six ameloblastomas (five follicular ameloblastomas and one plexiform ameloblastoma) and three malignant odontogenic tumors (one metastasizing ameloblastoma, one ameloblastic carcinoma, and one primary intraosseous odontogenic carcinoma) were investigated for CTNNB1 expression and CTNNB1 mutation. Immunohistochemically, all follicular ameloblastomas and one primary intraosseous odontogenic carcinoma exhibited focal and moderate nuclear/cytoplasmic expression of CTNNB1, whereas the plexiform ameloblastoma and the remaining two malignant odontogenic tumors had entirely membranous expression. CTNNB1 mutation at codon 40 of exon 3 was found in one of the six follicular ameloblastomas. The other five follicular ameloblastomas, the plexiform ameloblastoma, and the three malignant odontogenic tumors did not show mutation in exon 3 of CTNNB1. These findings further confirmed that CTNNB1 mutation is not frequent in ameloblastoma and malignant odontogenic tumors, although the abnormality of Wnt signaling may be associated with some of these tumors.     

Co-expression of hepatocyte growth factor and c-met in epithelial odontogenic tumors

Hepatocyte growth factor (HGF) and its receptor, c-met, have been shown to regulate cell proliferation, motility and morphology in a variety of cell types. A significant role of the HGF/c-met pathway has been demonstrated in various tumors, however, little is known about the role of HGF/c-met pathway in odontogenic tumors. The aim of this study was to characterize the expression of HGF and c-met in 30 ameloblastomas, 7 unicystic ameloblastomas (luminal type), 10 calcifying cystic odontogenic tumors, 10 adenomatoid odontogenic tumors (AOTs), 30 keratocytic odontogenic tumors (KCOTs) and 6 ameloblastic carcinomas using an immunohistochemical method. HGF and c-met were generally immunolocalized in the cytoplasm of all epithelial tumor cells, except for keratinizing cells in acanthomatous ameloblastoma, in all the examined odontogenic tumors. These results, together with the expression of these two proteins in the epithelium of tooth germs, suggest that the HGF/c-met pathway is involved in the differentiation of odontogenic tumors. This pathway may also promote tumor proliferation in odontogenic tumors due to its potent mitogenic effect. The consistent and strong immunolocalization of HGF and c-met in squamous cells present in acanthomatous ameloblastomas, AOTs and ameloblastic carcinomas, and in the linings of KCOTs suggests that the HGF/c-met interaction may have an influence on squamous differentiation in these odontogenic tumors.     

Midkine expression correlating with growth activity and tooth morphogenesis in odontogenic tumors

Midkine (MK; a low molecular weight heparin-binding growth factor) is a multifunctional cytokine. MK plays a role in morphogenesis of many organs including teeth through epithelial-mesenchymal interactions. We immunohistochemically examined MK expression in various human odontogenic tumors. There was no difference in positive rate and intensity of MK between benign odontogenic tumors and their malignant counterparts. Ameloblastoma showed MK localization in the peripheral columnar cells in budding processes from the parenchyma, which frequently expressed proliferating cell nuclear antigen. MK was also preferentially expressed in keratinized cells in acanthomatous ameloblastoma and keratocystic odontogenic tumor. In odontogenic mixed tumors except for odontoma, intense immunoreactivity to MK was found in epithelial follicles, the surrounding odontogenic ectomesenchymal tissue, and the basement membrane between them. Intensity in the odontogenic ectomesenchyme decreased in relation to distance from the epithelial follicles. No expression was found in tumor cells associated with production of dental hard tissues in odontogenic mixed tumors including odontoma. These findings suggested that MK is involved in the reciprocal interaction between odontogenic epithelium and odontogenic ectomesenchymal tissue in areas without dental hard tissue formation in odontogenic mixed tumors. Coexpression of MK and proliferating cell nuclear antigen was also observed in epithelial follicles and highly cellular nodules in the ectomesenchyme of odontogenic mixed tumors. MK is considered to mediate growth activity of odontogenic tumors and cell differentiation of odontogenic mixed tumors through molecular mechanisms similar to those involved in morphogenesis of the tooth.     

Relative frequency of odontogenic tumors in Sri Lanka: Analysis of 1677 cases

Odontogenic tumors (OTs) constitute a heterogeneous group of lesions with diverse histopathological features and clinical manifestations. The present study is to determine the frequency of odontogenic tumors (OTs) in Sri Lankan population. A total of 1677 cases of OTs were retrieved and analyzed for age, gender and primary site of the tumors. Cases were re-classified according to the 2005 WHO classification of OTs. The relative frequency of different types of tumors was also analyzed and compared with the literature. OTs represent 3.75% of all cases received during a period of 30 years. Ninety-eight percent of these tumors were benign and the rest malignant. Mandible to maxilla ratio is 2.8:1. The posterior part, the molar region, is the most frequently affected site for the mandible whilst it is the anterior region for the maxilla. The age ranges from 1 to 80 years, with a mean age of 30.6 years. Ameloblastoma of solid/multicystic and unicystic types showed a high preponderance for the mandible (>90%) with a ratio of 12.9:1 and 10.8:1, respectively. Out of 1677 cases, 48.7% were ameloblastoma, and other tumors, such as keratocystic odontogenic tumor (KCOT) and odontoma, were 25.7% and 10.1%, respectively. There is a significant change in the frequency of OTs after the inclusion of odontogenic keratocyst as a tumor. Although odontoma is said to be the commonest in western countries, our results showed ameloblastoma as the commonest followed by KCOT, and the relative frequencies of different tumors have changed significantly as a result of inclusion of KCOT in the new classification.     

Immunohistochemical demonstration of an enamel sheath protein, sheathlin, in odontogenic tumors

Enamel proteins can be useful markers for assessment of the functional differentiation of neoplastic epithelium and the nature of extracellular matrices in odontogenic tumors. In the present study, we examined immunohistochemical localization of sheathlin, a recently cloned enamel sheath protein, in various odontogenic tumors to evaluate functional differentiation of tumor cells and the nature of hyalinous or calcified matrices in odontogenic neoplasms. Distinct immunolocalization of sheathlin was observed in the immature enamel of the tooth germ at the late bell stage. Secretory ameloblasts facing the enamel matrix also showed positive staining in their cytoplasm. Definite localization of sheathlin was demonstrated in the enamel matrix in odontogenic tumors with inductive dental hard tissue formation such as ameloblastic fibroodontomas and odontomas. Immunoexpression of sheathlin was, furthermore, demonstrated in eosinophilic droplets in solid nests of adenomatoid odontogenic tumor (AOT) and ghost cells in the epithelial lining of calcifying odontogenic cyst (COC). In AOT, cells facing the eosinophilic droplets also expressed the protein in their cytoplasm. There was neither intracellular staining for sheathlin in the tumor cells nor extracellular staining in the matrix of ameloblastomas and calcifying epithelial odontogenic tumors. Dentin, dysplastic dentin-like hyaline material and cementum in the tumors examined were negative for sheathlin. These results show that immunodetection of sheathlin is a useful marker for functional differentiation of secretory ameloblasts and enamel matrix, which is often hard to differentiate from other hard tissues in odontogenic tumors. Our findings from the view point of sheathlin expression support that the tumor cells of ameloblastomas do not attain full differentiation into functional ameloblasts. It is very interesting that epithelial cells in odontogenic tumors can differentiate into functional ameloblasts without induction by odontogenic mesenchyme, as shown by immunoexpression of sheathlin in eosinophilic droplets within solid epithelial sheets in AOT and ghost cells in the epithelial lining of COC where inductive participation of mesenchymal cells was most unlikely. Received: 19 May 1999 / Accepted: 27 September 1999     

Expression of Vesicular Nucleotide Transporter in Rat Odontoblasts

Several theories have been proposed regarding pain transmission mechanisms in tooth. However, the exact signaling mechanism from odontoblasts to pulp nerves remains to be clarified. Recently, ATP-associated pain transmission has been reported, but it is unclear whether ATP is involved in tooth pain transmission. In the present study, we focused on the vesicular nucleotide transporter (VNUT), a transporter of ATP into vesicles, and examined whether VNUT was involved in ATP release from odontoblasts. We examined the expression of VNUT in rat pulp by RT-PCR and immunostaining. ATP release from cultured odontoblast-like cells with heat stimulation was evaluated using ATP luciferase methods. VNUT was expressed in pulp tissue, and the distribution of VNUT-immunopositive vesicles was confirmed in odontoblasts. In odontoblasts, some VNUT-immunopositive vesicles were colocalized with membrane fusion proteins. Additionally P2X₃, an ATP receptor, immunopositive axons were distributed between odontoblasts. The ATP release by thermal stimulation from odontoblast-like cells was inhibited by the addition of siRNA for VNUT. These findings suggest that cytosolic ATP is transported by VNUT and that the ATP in the vesicles is then released from odontoblasts to ATP receptors on axons. ATP vesicle transport in odontoblasts seems to be a key mechanism for signal transduction from odontoblasts to axons in the pulp.     

Evidence of Two Types of Odontoblasts during Dentinogenesis in Elasmobranchs

The fine structure of the odontoblasts in the sting rays, Dasyatis akajei Dasyatidae, and Urolophus aurantiacus Urolophidae, was examined using light and transmission electron microscopy. In the dentinogenesis stage, the odontoblasts have been classified into two types, that is, dark cells and light cells, based on differences in their fine structure. Many dark odontoblasts found along the predentine displayed well-developed organelles with secretory activity around the nuclei. They contained large amounts of expanded rER, widely distributed Golgi apparatus and secretory granules. In contrast, light odontoblasts showed a relatively clear cytoplasm and extended long processes which passed through the predentine and penetrated into the dentine. They contained large numbers of microtubules in the processes and many mitochondria around the nuclei. It is suggested that the light odontoblasts play an important part in material transport to the dentine and/or act as a sensory organ of the tooth. The dark odontoblasts seem to produce the organic matrix of the dentine and to prepare for mineralization in the dentine.     

Immunohistochemical detection of laminin-1 and Ki-67 in radicular cysts and keratocystic odontogenic tumors

Background  

Odontogenic cysts are those which arise from the epithelium associated with the development of teeth. Some odontogenic cysts were found to have special biological features that make them distinct from other lesions. This study was conducted to detect the immunoepxression of laminin-1 and Ki-67 in both radicular cysts (RCs) and keratocystic odontogenic tumors (KCOTs) and to examine the possible predictive value of these markers.     

Ghost cell odontogenic carcinoma arising in calcifying odontogenic cyst

A case of exceptionally rare odontogenic malignant tumor, called ghost cell odontogenic carcinoma, is described. The tumor was considered to be derived from calcifying odontogenic cyst, which had been resected 5 years before. In the present resected specimen, cellular atypia, mitotic activity, Ki-67 labeling index, and p53 positivity were all increased in comparison with the initially resected specimen. This is a valuable case in which malignant transformation from calcifying odontogenic cyst to ghost cell odontogenic carcinoma was proven by the histopathologic and immunohistochemical findings. Pathologists should be aware of this rare entity.     

Dentin Mineralization and the Role of Odontoblasts in Calcium Transport

Dentin is formed by two simultaneous processes, in which the odontoblasts are instrumental—the formation of the collagenous matrix, and mineral crystal formation in this matrix. This pattern of formation is similar to that of bone, another mineralized connective tissue. Dentin and bone also have chemical compositions which are similar but with distinct differences. It is of fundamental importance to understand how the ions constituting the inorganic phase are transported from the circulation to the site of mineral formation and how this transport is regulated. For dentinogenesis, calcium is essentially the only ion for which data are available. Recent evidence suggests that a major portion of the Ca²⁺ ions are transported by a transcellular route, thus being under cellular control. The cells maintain a delicate Ca²⁺ ion balance by the concerted action of transmembraneous transport mechanisms, including Ca-ATPase, Na⁺/Ca²⁺ exchangers and calcium channels, and of intracellular Ca²⁺-binding proteins. The net effect of this is a maintenance of a sub-micromolar intracellular Ca²⁺ activity, and an extracellular accumulation of Ca²⁺ ions in predentin, at the mineralization front. Predentin can be regarded as a zone of formation and maturation of the scaffolding collagen web of the dentin organic matrix. In addition to collagen, it contains little but proteoglycan. Simultaneous with mineral formation, additional non-collagenous macromolecules are added to the extracellular matrix of dentin, these presumably being transported within the odontoblast process. Among these are highly phosphorylated dentin phosphoprotein (phospho-phoryn) and another pool of proteoglycan. The functionality of this may be explained by the fact that polyanionic macromolecules are capable of inducing the formation of hydroxyapatite at ionic conditions resembling those in vivo. They can also inhibit mineral growth and regulate crystal size.