Comparative expression of calretinin in selected odontogenic tumours: a possible relationship to histogenesis

Aims:  Calretinin, a calcium-binding protein, is expressed primarily in certain subtypes of neurons. It has also been reported to be present in mesotheliomas and other tumours. The aim was to determine the expression of calretinin in selected odontogenic neoplasms.
Methods and results:  Immunohistochemistry for calretinin was performed on 55 odontogenic tumours consisting of 20 solid ameloblastomas, five calcifying epithelial odontogenic tumours, 10 adenomatoid odontogenic tumours, 10 ameloblastic fibromas and 10 odontogenic myxomas. The distribution, intensity, pattern and localization of immunoreactive cells were determined by conventional light microscopy. χ² test was used for statistical analysis and P  < 0.05 was considered to be significant. All 20 ameloblastomas showed intense immunopositivity with a diffuse distribution pattern. None of the other neoplasms was reactive with calretinin. Differences in the proportion of calretinin expression between groups were statistically significant at P  < 0.001.
Conclusions:  Considering that ameloblastomas, in contrast to the other studied tumours, were consistently reactive for calretinin, this protein may have a role in the pathogenesis of this aggressive neoplasm.     

Expression of epidermal growth factor receptors by odontogenic jaw cysts

The expression of epidermal growth factor receptor (EGFr) by odontogenic epithelium was studied in odontogenic cysts (n=35), ameloblastoma (n=6), and periapical granulomas containing proliferating epithelial rests of Malassez (n=7) using a panel of monoclonal antibodies to EGFr (clone E30, F4 and C11) known to react with formalin-fixed, paraffin-embedded sections. Odontogenic epithelium in all specimens demonstrated immunoreactivity with all three antibodies. Clone E30 consistently gave the most intense, membrane located staining pattern of the three antibodies tested. Generally, staining of epithelial cells progressively diminished with movement away from the basal cell layers toward the most superficial layers of cystic lining or centre of epithelial rests and tumour islands. Developmental odontogenic cysts (odontogenic keratocysts,n= 13; dentigerous cysts,n=11) and ameloblastoma (follicular type,n=5; unicystic type,n=1) expressed a higher level of EGFr staining than inflammatory cysts (radicular cysts,n=11) and the proliferating epithelial rests in periapical granulomas. However, foci of weak EGFr staining of odontogenic keratocyst lining, similar to that seen in radicular cysts, were found in areas associated with inflammation. In addition, epithelial rests not associated with inflammatory cell infiltrates exhibited stronger reactivity for EGFr than proliferating rests within periapical granulomas. These results indicate that the level of EGFr expression by odontogenic cysts and rests is related to the presence of inflammation within adjacent connective tissue and that there is no detectable difference in receptor expression between developmental cysts and ameloblastoma.     

Immunohistochemical expression of amelogenins in odontogenic epithelial tumours and cysts

Summary Amelogenins, enamel proteins in odontogenic tumours, were detected immunohistochemically using a monoclonal antibody. They were strongly expressed in amyloid-like material, ghost cells, and the cells surrounding ghost cells of calcifying epithelial odontogenic tumours and cysts, whereas calcified bodies within the tumours and cysts showed negative staining. The expression of amelogenins was also positive in tumour cells of ameloblastoma, adenomatoid odontogenic tumour, squamous odontogenic tumour and ameloblastic fibroma. Peripheral tumour cells of the follicular ameloblastoma were positive with relatively intense staining. Undifferentiated or flattened tumour cells of adenomatoid odontogenic tumour and non-keratinized tumour cells of the squamous odontogenic tumour showed marked staining. Reduced ameloblasts in the odontoma displayed the strongest staining for amelogenins. The study suggests that biosynthesis of amelogenins may occur in the homogeneous materials of calcifying epithelial odontogenic tumours and cysts.     

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.     

An orderly approach to the study of odontogenic tumours in animals.

In this paper odontogenic tumours in animals are discussed with the aim of developing a sound basis for further work in this relatively poorly understood field. The following recommendations are made: (1) Odontogenic tumours should be classified according to whether they are of epithelial, mesenchymal or of mixed epithelial and mesenchymal origin, rather than based on inductive changes. (2) The clinical behaviour implied by ameloblastoma, ameloblastic fibroma and odontoma should be carefully considered before these terms are incorporated into the diagnosis of any odontogenic tumour. (3) Caution should be exercised in designating specific odontogenic tumours in animals as being the counterpart of human tumours until their histopathological features and clinical behaviour have been proved to be equivalent. (4) Only tumours that exhibit the typical features of the basal cell layer of ameloblastomas should be designated as ameloblastomas. (5) Ameloblastic epithelium should not be used when odontogenic epithelium is intended. (6) These recommendations should be substantiated by reviewing odontogenic tumours in animals, although doing so will be difficult because of their rarity.     

Combined immunohistochemistry for the differential diagnosis of cystic jaw lesions: its practical use in surgical pathology

Tsuneki M, Yamazaki M, Cheng J, Maruyama S, Kobayashi T & Saku T
(2010) Histopathology 57, 806–813 Combined immunohistochemistry for the differential diagnosis of cystic jaw lesions: its practical use in surgical pathology Aims: Histopathological distinction of cystic jaw lesions, including odontogenic tumours, is challenging because their lining epithelia, which are basically stratified squamous epithelia, resemble each other, especially when they become hyperplastic from inflammatory reaction. The aim of this study was to seek practical measures to differentiate such lesions. Methods and results: Nineteen surgical specimens from unicystic ameloblastomas (UAs), 17 from keratocystic odontogenic tumours (KCOTs), 13 from dentigerous cysts (DCs), 10 from lateral periodontal cysts (LPCs) and 20 from radicular cysts (RCs), all of which contained both typical flat and rete‐peg‐shaped lining epithelia, were examined for their immunohistochemical profiles. Among them, keratin (K) 10, K17, perlecan, proliferating cell nuclear antigen (PCNA) and UEA‐I lectin binding (UEA) were selected as useful immunohistochemical markers for their differential diagnosis. K10 was positive (+) in KCOT and DC. K17 was not present in RC. Perlecan was found in UA, KCOT and LPC. PCNA+ cells were found frequently in UA and KCOT. These localization patterns were constant even when linings were not flat. Conclusions: Using a combination of six kinds of immunohistochemical pattern, it is now possible to discriminate reliably and objectively these five cystic jaw lesions in routine practice.     

Granular cells in odontogenic and non-odontogenic tumours

Summary Granular cells can occur in various odontogenic and non-odontogenic tumours. 5 granular cell lesions, one granular cell ameloblastoma, one so-called granular cell ameloblastic fibroma and three granular cell tumours were examined immunohistochemically for the intermediate filaments cytokeratin, vimentin, desmin, neurofilaments and the neural markers NSE and S-100 protein. The granular cell tumors (granular cell myoblastoma) showed positive staining for vimentin and S-100 protein. Only vimentin could be demonstrated in the granular cells of the so-called granular cell ameloblastic fibroma, whereas the granular cell ameloblastoma showed positive staining only for cytokeratin. A positive reaction with S-100 protein was not found in any of the odontogenic tumours. In our opinion the mesenchymal odontogenic granular cell is a fibroblast, whereas the epithelial granular cell is derived from enamel epithelium. The term granular cell ameloblastic fibroma is a misnomer, as a number of these tumours are probably central odontogenic fibromas exhibiting granular cell transformation.     

Immunohistochemical localization of large chondroitin sulfate proteoglycan in odontogenic tumor

The present study investigated the localization of versican in odontogenic tumors by immunohistochemistry, using paraffin-embedded sections obtained from 27 patients with odontogenic tumors (17 ameloblastomas, 1 adenomatoid odontogenic tumor, 4 odontogenic keratocysts, 1 calcifying odontogenic cyst, 2 ameloblastic fibromas, and 2 malignant ameloblastomas). Deparaffinized sections were immersed in a buffered 1 : 1000 solution of an antibody, 5D5 (raised against a large chondroitin sulfate proteoglycan from bovine sclera), which mainly recognizes versican. All samples showed a positive reaction for versican in connective tissues, whereas positive staining of epithelial nests was observed in only some samples. The positive staining in epithelial nests was in areas showing stellate reticulum-like, cuboidal, columnar cells at the periphery, and tear-drop structures. These results indicated that versican might be involved in, at least in part, the morphogenesis of neoplastic epithelium and mesenchymal tissues in odontogenic tumors.     

Odontogenic classification of craniopharyngiomas: a clinicopathological study of 54 cases

Based on the striking histological similarity of craniopharyngiomas and some odontogenic tumours, we reclassified a series of 54 craniopharyngiomas (52 adamantinomatous and two papillary variants) according to the WHO classification of odontogenic tumours. Twenty-seven tumours (50%) corresponded histologically to calcifying odontogenic cyst, 13 tumours (24%) to ameloblastoma, and eight (15%) tumours showed features of both calcifying odontogenic cyst and ameloblastoma either within the same specimen or in specimens derived from different resections. Rare tumours included three cases resembling calcifying epithelial odontogenic tumour and one case resembling adenomatoid odontogenic tumour. No odontogenic counterpart could be established for papillary craniopharyngiomas. The two major subtypes, i.e. craniopharyngioma corresponding to calcifying odontogenic cyst and craniopharyngioma corresponding to ameloblastoma, did not differ in their basic clinical features. Our data confirm and extend the close histological resemblance between adamantinomatous craniopharyngioma and odontogenic tumours and cysts. Furthermore, although calcifying odontogenic cyst and ameloblastoma arising in the jaw differ in clinical presentation and outcome, our study did not reveal clinical differences for the corresponding subtypes of craniopharyngioma.     

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     

Epithelial odontogenic tumours in domestic animals

Epithelial odontogenic tumours are uncommon, poorly understood and often difficult to diagnose, oral neoplasms. Dental organ pre-ameloblasts and basal lamina induce development of mesenchymal cells into odontoblasts, which produce dentin and induce pre-ameloblasts to mature into secretory ameloblasts. These reciprocal sequential inductive interactions between dental epithelium and mesenchyme form the basis for classifying epithelial odontogenic tumours. There are three tumours classified as non-inductive: ameloblastoma characterized by cords and islands of stellate reticulum with peripheral palisades of polarized columnar cells, adenomatoid ameloblastoma which has acini, rosettes and ducts of polarized columnar cells and stellate reticulum and calcifying epithelial odontogenic tumour which contains foci of Congo-red-positive material surrounded by pleomorphic polygonal epithelial cells. There are five tumours in which induction of mesenchymal tissue is evident: ameloblastic fibroma with characteristics of ameloblastoma plus proliferation of closely associated pulp-like mesenchyme; dentinoma consisting of masses of dentin, often with minimal cellular component; ameloblastic odontoma which contains palisaded epithelium and stellate reticulum as in ameloblastoma, as well as foci of dentin and/or enamel; complex odontoma which is a disorderly array of dentin, enamel, ameloblastic epithelium and odontoblasts; and compound odontoma containing denticles with well-organized tooth morphology. This paper reviews the embryogenesis of teeth and describes six types of epithelial odontogenic tumours in 13 animals. The literature concerning these tumours in nearly 250 animals is reviewed. The most commonly reported tumour is ameloblastoma and the species in which all types are most commonly reported is the dog.     

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.     

CD56 (NCAM) expression in ameloblastomas and other odontogenic lesions

Cairns L, Naidu A, Robinson C M, Sloan P, Wright J M & Hunter K D
(2010) Histopathology 57, 544–548
CD56 (NCAM) expression in ameloblastomas and other odontogenic lesions Aims: Ameloblastomas recapitulate certain elements of tooth formation. CD56 is expressed by a variety of cells and is used in tumour diagnosis, but is also expressed in the enamel organ during tooth development. The aim of this study was to describe the expression of CD56 in odontogenic lesions with particular reference to the differential diagnosis of ameloblastoma and odontogenic keratocyst. Methods: Cases were selected from the pathology archives at Glasgow Royal Infirmary, Glasgow, Royal Victoria Infirmary, Newcastle and Department of Diagnostic Sciences, Texas A&M Health Science Center Baylor College of Dentistry, Dallas. The study population included 38 ameloblastomas, 19 odontogenic keratocysts and a number of other odontogenic lesions, including nine compound odontomes. All sections were examined for CD56 immunoreactivity and the extent of staining was recorded. Results: Thirty‐seven of 38 (97%) ameloblastomas expressed CD56 on the cell membrane of peripheral cells in tumour nests (16 extensively, 21 focally). Immunoreactivity was lost in areas of inflammation, acanthomatous differentiation, in areas of cystic change and upon fusion with overlying surface epithelium. One odontogenic keratocyst expressed CD56 (5%, P < 0.0001). CD56 was expressed very focally in two odontomes, exclusively in stratum intermedium‐like cells. Conclusions: CD56 expression in odontogenic epithelium is highly suggestive of ameloblastoma and can help in differentiating this from odontogenic keratocyst.     

Comprehensive keratin profiling reveals different histopathogenesis of keratocystic odontogenic tumor and orthokeratinized odontogenic cyst

Keratocystic odontogenic tumor is a cystic lesion that behaves more aggressively than other jaw cysts. One of its characteristic histologic features is a parakeratinized uniform layer of lining epithelium. A jaw cyst lined with orthokeratinized epithelium is called an orthokeratinized odontogenic cyst. These keratinized jaw cysts are thought to be separate entities, although their histopathogenesis has not been fully assessed. To better understand these lesions, we performed comprehensive immunohistochemical profiling of the keratin expression of each. Orthokeratinized odontogenic cysts expressed keratin 1, keratin 2, keratin 10, and loricrin, suggesting differentiation toward normal epidermis. Keratocystic odontogenic tumors expressed keratin 4, keratin 13, keratin 17, and keratin 19, which is a unique expression pattern reminiscent of a mucosal squamous epithelium and an epithelial appendage. In neonatal rat tooth germ, cells strongly positive for keratin 17 and keratin 19 were observed, specifically in the dental lamina, implying the origin of keratocystic odontogenic tumor. GLI2, a downstream effector of hedgehog signaling, was significantly expressed in keratocystic odontogenic tumor and basal cell carcinoma, accompanied with robust expression of keratin 17, mammalian target of rapamycin, and BCL2. The expression of these GLI2- or keratin 17-related factors was not significantly observed in orthokeratinized odontogenic cysts. These findings provide evidence to support the viewpoint that keratocystic odontogenic tumor and orthokeratinized odontogenic cyst are separate entities, and furthermore suggest their characteristic histology, pathogenesis, and biological behaviors.     

An unusual odontogenic cyst with diverse histologic features

An unusual odontogenic cyst, which was originally believed to be a clinical dentigerous cyst associated with an impacted mandibular third molar, was found histologically to demonstrate the characteristics of a glandular odontogenic cyst with para- and orthokeratinization. These histologic diversities were interpreted as a reflection of the pluripotentiality of the epithelial remnants of the mandibular third molars or dentigerous cyst epithelium. It is possible that it has the capacity to induce the formation of cysts in both squamous and glandular epithelium.     

Expression of proliferating cell nuclear antigen (PCNA) and Ki-67 in unicystic ameloblastoma

The expression of proliferating cell nuclear antigen (PCNA) and Ki-67 was studied in unicystic and solid ameloblastoma (follicular and plexiform types) using a biotin-streptavidin method on routinely processed paraffin sections. To determine percentage PCNA and Ki-67 labelling indices, positive tumour cells and total tumour cells were counted in areas of each unicystic ameloblastoma corresponding to cystic linings, intraluminal nodules and invading tumour islands, and in solid ameloblastomas. Positive cells in basal and suprabasal layers of cystic tumour lining were also counted with respect to the length of basement membrane determined by image analysis. In unicystic ameloblastoma the invading islands exhibited a significantly higher PCNA labelling index (29.2 ± 16.4%) than intraluminal nodules (13.6 ± 5.4%; P < 0.05). Cystic tumour lining had relatively few PCNA positive cells and a labelling index (5.5 ± 3.3%) significantly lower than invading islands (P < 0.001) or intraluminal nodules (P < 0.003). The labelling indices of solid ameloblastomas of follicular type (48.1 ± 12.9%) were significantly higher than those of cystic tumour lining (P < 0.0001), intraluminal nodules (P < 0.001) and invading islands (P < 0.04) in unicystic ameloblastoma. Similar relationships were found for Ki-67 expression except that comparisons involving invading islands and intraluminal nodules were not significant, a finding probably due to the smaller number of specimens available for quantitative analysis. These results indicate differences in proliferative potential between different areas of unicystic ameloblastoma and between unicystic and solid lesions. The fact that invading tumour islands within the fibrous tissue wall showed high labelling indices is in agreement with the clinical observation that their presence may be related to recurrence after conservative surgery. This provides a biological basis for indicating more radical surgical excision as the treatment of choice for this subgroup of lesions.     

Pathogenesis of Rushton bodies: A novel hypothesis

Rushton bodies (RBs) are one of the characteristic features seen in the epithelial lining of odontogenic cysts mainly radicular, dentigerous and odontogenic keratocyst. It has two different histo-morphological appearances; granular and homogeneous. Although widely investigated, the exact pathogenesis and histogenesis of RBs is still an enigma. Many hypotheses were made in the literature but none has explained conceivably the two histo-morphological appearances of RBs and their association with inflammation. In the present paper the various pathogenesis for the formation of RBs proposed till date are discussed along with proposal for a novel hypothesis. The given hypothesis is mainly related to inflammation and its effect on pore size of basement membrane of odontogenic cystic epithelium. It explains RBs association with inflammation as well as existence of two histo-morphological appearances. The proposed hypothesis also justifies the RB’s presence inside the lining epithelium of odontogenic cyst despite its hematogenous origin. Future studies are advocated for isolating RBs using laser capture microdissection and subsequent biochemical, histochemical and electron microscopic analysis to substantiate the proposed hypothesis.