Patterns of expression of intermediate filaments in ameloblastoma and human fetal tooth germ

Proceedings of the 2023 Division of Translational Toxicology Satellite Symposium

The 2023 annual Division of Translational Toxicology (DTT) Satellite Symposium, entitled "Pathology Potpourri," was held in Summerlin, Nevada, at the Society of Toxicologic Pathology's 41st annual meeting. The goal of this symposium was to present and discuss challenging diagnostic pathology and/or nomenclature issues. This article presents summaries of the speakers' talks along with select images that were used by the audience for voting and discussion. Various lesions and topics covered during the symposium included induced and spontaneous neoplastic and nonneoplastic lesions in the mouse liver, infectious and proliferative lesions in nonhuman primates, interesting presentations of mononuclear cell infiltrates in various animal models and a complex oral tumor in a rat.

Ameloblastic carcinoma in horses: case report and literature review

Ameloblastic carcinoma is a malignant odontogenic neoplasm that has been reported only rarely in veterinary species. A 16-y-old Arabian crossbred mare was presented for evaluation of a hard mass on the body of the mandible, with evidence of osteolysis on radiographs. Incisional biopsies revealed an invasive neoplasm comprised of spindloid epithelial cells with a high mitotic count and partial dual cytokeratin-vimentin immunoreactivity. The horse was euthanized because of rapid tumor progression 3 mo after presentation. Postmortem evaluation revealed partial obliteration of the mandible by a large, firm-to-hard, tan, locally destructive and invasive mass with no gross or histologic evidence of metastasis. Postmortem histology revealed a poorly differentiated epithelial neoplasm with variably prominent features suggestive of odontogenic histogenesis: a plexiform ribbon architecture, infrequent basilar palisading with antibasilar nuclei, rare basilar cytoplasmic clearing, subepithelial matrix hyalinization, and partial dual cytokeratin-vimentin immunoreactivity. Features of malignancy included regions of necrosis, pronounced cellular atypia, a high mitotic count, extensive tissue invasion and local tissue destruction, and extension of neoplastic cells beyond the margins of the mandibular bone. Collectively, these features are most consistent with mandibular ameloblastic carcinoma. Including our case described here, ameloblastic carcinoma has been reported in only 5 horses. The microscopic features reported most consistently are dual cytokeratin-vimentin immunoreactivity, a high mitotic count, and basilar palisading. Ameloblastic carcinoma should be considered as a differential diagnosis for rapidly growing, locally invasive masses arising from the dentate jaw of horses.

The mechanism: how dental resorptions occur in ameloblastoma

Knife-edge or blunt root resorptions characterize ameloblastomas and are pathognomonic for this tumor, because they differentiate ameloblastomas from simple bone cysts, odontogenic keratocysts and nasopalatine duct cysts, which do not lead to resorption of involved teeth. Despite the very high frequency and importance of these characteristics for a differential diagnosis, a microscopic examination should also be conducted before defining the diagnosis and the treatment plan for these cases. This paper describes a six-step hypothesis to explain the mechanism by which ameloblastomas promote the characteristic root resorptions found in association with these benign epithelial tumors, which have a fibrous capsule formed by islands and epithelial cords that mimic the dental lamina, invade neighboring tissues and release mediators (IL-1, EGF) of tooth and root resorption. This hypothesis may be one more explanation for the tooth resorptions sometimes found in orthodontic records, and may help differentiate the root resorptions that are specific to the orthodontic practice.

Primordial odontogenic tumor: An immunohistochemical profile

BACKGROUND

Primordial Odontogenic Tumor (POT) is a recently described odontogenic tumor characterized by a variably cellular loose fibrous tissue with areas similar to the dental papilla, covered by cuboidal to columnar epithelium that resembles the internal epithelium of the enamel organ, surrounded at least partly by a delicate fibrous capsule. The purpose of this study was to investigate the possible histogenesis and biological behavior of this rare tumor by means of a wide immunohistochemical analysis of its epithelial and mesenchymal components.

MATERIAL AND METHODS

The immunoexpression of twenty-three different antibodies were evaluated in four cases of POT.

RESULTS

The epithelial cells that cover the periphery of the tumor showed immunopositivity for Cytokeratins 14 and 19, while Amelogenin, Glut-1, MOC-31, Caveolin-1. Galectin-3, PITX2, p53, Bax, Bcl-2, Survivin and PTEN were variably expressed in focal areas. The mesenchymal component of the tumor was positive for Vimentin, Syndecan-1, PITX2, Endoglin (CD105), CD 34, Cyclin D1, Bax, Bcl-2, Survivin and p53. PTEN and CD 90 showed a moderate positivity. BRAF V600E and Calretinin were negative in all samples. Cell proliferation markers (Ki-67, MCM-7) were expressed in <5% of the tumor cells.

CONCLUSIONS

According to these immunohistochemical findings, we may conclude that POT is a benign odontogenic tumor in which there is both epithelial and mesenchymal activity during its histogenesis, as there is expression of certain components in particular zones in both tissues that suggests this tumor develops during the immature (primordial) stage of tooth development, leading to its inclusion within the group of benign mixed epithelial and mesenchymal odontogenic tumours in the current World Health Organization classification of these lesions.

Maxillary Ameloblastic Carcinoma in an Alaskan Malamute

A 3-year-old female Alaskan Malamute was submitted to the Veterinary Teaching Hospital of Madrid with a mass in the right maxilla. It was ulcerated, covered by a yellowish infected membrane, and painful. The histologic examination showed a neoplastic proliferation of palisading cells distributed irregularly in cords. The tumor was diagnosed as an ameloblastic carcinoma because of the histologic signs of malignancy, the aggressive behavior, and the absence of distal metastasis. This is the first description of an ameloblastic carcinoma in a dog.

Expression of cytokeratin 8, vimentin, syndecan-1 and Ki-67 during human tooth development

Spatio-temporal immunolocalizations of cytokeratin 8 (CK8), vimentin, syndecan-1 and Ki-67 were analyzed in ten human incisors and canine tooth germs between the 7th and 20th developmental weeks. CK8 expression was mild to moderate in the epithelial tooth parts, while it shifted from absent or mild in its mesenchymal parts, but few cells, sparsely distributed throughout the tooth germ, strongly expressed CK8. As development progressed, CK8 expression increased to strong in preameloblasts, while expression of vimentin increased to moderate in the epithelial and mesenchymal tooth parts, particularly in the dental papilla and sac. Co-expression of CK8 and vimentin was observed in some parts of the tooth germ, and was increasing in the differentiating preameloblasts and preodontoblasts. Syndecan-1 showed characteristic shift of expression from epithelial to mesenchymal tooth parts, being particularly strong in dental papilla, sac and cervical loops, while co-expression of Ki-67/syndecan-1 was strong in the dental papilla. Our study demonstrated spatio-temporal expression and restricted co-expression of the investigated markers, indicating participation of CK8 and vimentin in cell proliferation and migration, and differentiation of preodontoblasts and preameloblasts. Our data also suggest involvement of syndecan-1 in morphogenesis of the developing tooth crown and cervical loops, and together with CK8 and vimentin in differentiation of preameloblasts and preodontoblasts.

Pathogenesis and nomenclature of odontogenic carcinomas: revisited

Odontogenic carcinoma is rare group of malignant epithelial odontogenic neoplasms with characteristic clinical behavior and histological features, which requires an aggressive surgical approach. The pathogenesis of this rare group remains still controversial and there have been many varied opinions over the classification of this rare group of lesions. As there have not been many reviews on odontogenic carcinoma, the existing knowledge is mostly derived from the published case reports. This review is discussing the pathogenetic mechanisms and is updating the knowledge on nomenclature system of less explored odontogenic carcinomas. This review might throw light on the pathogenesis and nomenclature system of odontogenic carcinoma and this knowledge may be applied therapeutically.

Ameloblastomas: clinical-histopathological evaluation of 85 cases with emphasis on squamous metaplasia and keratinization aspects

OBJECTIVES

Ameloblastoma is a benign odontogenic neoplasm with an origin reputed to reactivation of odontogenic structures. Histological classification is based on microscopic features and architectural distribution of neoplastic cells. The importance of squamous metaplasia and keratinization has been disputed in ameloblastomas. Clinical and histopathological aspects were evaluated of 85 ameloblastomas, with attention to keratinization and squamous metaplasia features.

STUDY DESIGN

Clinical-demographical information of 85 ameloblastomas were gleaned from the medical records. Microscopic analysis of all cases was carried out with emphasis on keratinization aspects of each tumor.

RESULTS

Most ameloblastomas (54.12%) were diagnosed in males with a mean age of 37 years. Fifty-six patients were Caucasians (65.88%) and the mandible was affected in 68 (89.4%) cases. Most cases analyzed presented areas of squamous metaplasia/keratinization. Recurrence was detected in 16 cases; this was not related to keratinization aspects of the tumor.

CONCLUSIONS

Keratinization is a common feature in ameloblastomas with no impact in tumor behavior.

The expression profiles of acidic epithelial keratins in ameloblastoma

OBJECTIVE

To characterize the subtypes of ameloblastoma by differentiation markers.

STUDY DESIGN

Expression of 9 major acidic epithelial keratins was immunohistochemically examined in 28 ameloblastomas.

RESULTS

Keratin 15 (K15) expression patterns corresponded to histological variants: follicular, plexiform and acanthomatous. Tumor nests comprising K15-expressing basal cells mimicked oral epithelium or dental lamina, and tumor nests comprising K15-negative basal cells mimicked outer enamel epithelium. Keratin 19 (K19) was consistently expressed in solid/multicystic ameloblastoma and unicystic ameloblastoma, while peripheral ameloblastoma and desmoplastic ameloblastoma contained K19-negative cells.

CONCLUSIONS

The 4 current subtypes had unvaried expression patterns within each group. However, they could be divided into 2 groups by K19 expression pattern: solid/multicystic and unicystic versus extraosseous/peripheral and desmoplastic. K15 expression pattern represented various types of differentiation for tumor nests mimicking tooth germ and oral epithelium. The results clarify the homogeneity and heterogeneity of ameloblastoma cell lineage and differentiation.

A histopathological and immunohistochemical analysis of ameloblastic fibrodentinoma

Ameloblastic fibrodentinoma (AFD) is considered a mixed odontogenic tumor that is characterized by conserved epithelial and ectomesenchymal neoplastic components. AFD is composed of long narrow cords and islands of odontogenic epithelium; the epithelial strands lie in a myxoid cell-rich ectomesenchymal tissue with stellate-shaped fibroblasts that exhibit long slender cytoplasmic extensions that resemble dental papilla. The lesions show the presence of dysplastic dentin. Although AFD is a rare entity and its very existence is not completely accepted, based on the extent of histodifferentiation, it is considered to represent a stage between ameloblastic fibroma and ameloblastic fibroodontoma. This study aimed to provide a histopathological and immunohistochemical characterization of this infrequent tumor. A large panel of antibodies including amelogenin, Ck 19, calretinin, syndecan-1, E-cadherin, MSH2, histone H3, and Ki-67 was used to illustrate the nature of the tumor.

Spindle cell ameloblastic carcinoma in a labrador retriever dog

A 13-year-old castrated male Labrador retriever dog presented with a mass caudal to the first molar of his left mandible. Although the tumor was excised, a recurrent tumor was detected one month later and resected. Both tumors displayed invasive growth and were composed of neoplastic proliferation arranged in irregular lobules, nests and cords continuous with mucosal epithelium. The most prominent feature of the tumors was the presence of many proliferating spindle cells admixed with palisading basal-like cells, acanthocytes and stellate cells. In immunohistochemical examinations, the spindle cells were found to be positive for vimentin; cytokeratin AE1/AE3, 5/6, 14 and 19; and p63. The other neoplastic cells were positive for all of these markers shown above except vimentin. Based on these findings, the tumors were diagnosed as spindle cell ameloblastic carcinoma.

Comparative immunohistochemical study of ameloblastoma and ameloblastic carcinoma

OBJECTIVE

Ameloblastic carcinoma combines the histologic features of ameloblastoma with cytologic atypia, regardless of whether it has metastasized. Because of its rarity, there are few immunoprofile studies of ameloblastic carcinoma and few comparative studies of ameloblastic carcinoma and ameloblastoma. In this study, we compared the expression levels of cytokeratins (CKs), matrix metalloproteinases (MMPs), and Ki-67 between ameloblastoma and ameloblastic carcinoma, and assessed the usefulness of these markers for differentiating the tumors.

STUDY DESIGN

We assessed CK7, CK14, CK18, CK19, MMP-2, MMP-9, and Ki-67 expression by immunohistochemistry in 10 cases of ameloblastoma and 7 cases of ameloblastic carcinoma and then compared expression patterns between the 2 groups.

RESULTS

Immunostaining for CK14 and CK19 was diffuse and strongly positive in both tumor types, but staining for CK7 was focally positive in only 1 case of ameloblastoma and absent in all cases of ameloblastic carcinoma. However, there was a significant difference in CK18 expression between the 2 tumors (P = .000). Whereas 80% of ameloblastomas showed negative reactivity for CK18, most cases of ameloblastic carcinomas showed a moderate to strong intensity of immunostaining for CK18. Regarding the expression of MMPs, there were significant differences in parenchymal MMP-2 and stromal MMP-9 expression between the 2 tumors. Compared to ameloblastoma, ameloblastic carcinoma showed significantly strong expression of MMP-2 in parenchymal cells (P = .001) and MMP-9 in stromal cells (P = .013). However, there were no differences in MMP-2 expression of stromal cells and MMP-9 expression of parenchymal cells between ameloblastoma and ameloblastic carcinoma. The mean Ki-67 labeling index (LI) of ameloblastic carcinomas was 17.21%, which was significantly higher than that of ameloblastomas (3.57%; P = .002).

CONCLUSIONS

The significant expression of CK18, parenchymal MMP-2, stromal MMP-9, and Ki-67 could provide useful markers for differentiating ameloblastic carcinoma from ameloblastoma.

Immunohistochemical localization of cytokeratins in the junctional region of ectoderm and endoderm

Although tridermic species have two junctional regions of ectoderm and endoderm between their epidermis and digestive tract, we actually know little about these particular boundaries. Cytokeratins are the major intermediate filaments of epithelial cells and show a high degree of tissue specificity. Therefore, to characterize the epithelial cells in the junctional region of ectoderm and endoderm, we immunohistochemically examined the localization of cytokeratins 5, 7/17, 14, 18, Sox17, and alpha-fetoprotein (AFP) in the oropharyngeal and anorectal regions during the mouse gastrulation process. At embryonic day (E) 9.5, cytokeratins 5, 7/17, 14, and 18 were detected in all epithelial cells of the oropharyngeal region. At E12.5, cytokeratin 5-positive cells were not observed in the middle area of the oral cavity; however, the immunoreactivity was strong in the anterior and posterior areas. The immunoreaction of cytokeratins 18 was seen only in the middle and posterior areas of the oral mucosa. Cytokeratins 7/17 and 14 were localized in all areas of the oropharyngeal region. Sox17 and AFP, which are endodermal markers, were detected in the middle and posterior areas of the oral mucosa, but not in the anterior area. Moreover, this same localization pattern of cytokeratins also existed in the anorectal region of the E12.5 embryo, suggesting that the localization of cytokeratins and endodermal markers might give an implication for the boundary between ectoderm and endoderm. These results also suggest that these cytokeratins are useful molecules for monitoring the epithelial cell differentiation in the junctional region of the germ layers.

Immunohistochemical profile of odontogenic epithelium in developing dog teeth (Canis familiaris)

Tumors of the jaw bones and oral soft tissue are relatively common lesions in dogs. The aim of this study was to find cell markers to differentiate odontogenic epithelium from nonodontogenic epithelium for future research on the pathogenesis and pathology of odontogenic neoplasms in dogs. Keratin 14 and 19 staining was observed in odontogenic and nonodontogenic epithelium, whereas amelogenin and p75 neurotrophin receptor immunoreactivity was observed in certain odontogenic epithelial cells at various stages of development but not in other epithelial cells. Calretinin staining was observed in the alveolar epithelial cells directly overlying the developing tooth germ in 28 of 39 sections (71.8%), as well as the dental laminae in 30 of 35 sections (85.7%) and Serres rests in 24 of 28 sections (85.7%). Focal positivity was detected in the respiratory mucosa, some hair follicles, and fusion epithelium of the palate, but no calretinin staining was observed in other oral epithelial cells; therefore, calretinin has potential to be utilized as a marker to differentiate odontogenic form nonodontogenic epithelium.

Clear cell odontogenic carcinoma: case report with immunohistochemical findings adding support to the challenging diagnosis

Clear cell odontogenic carcinoma (CCOC) is a rare odontogenic tumor associated with aggressive clinical behavior, metastasis, and low survival. We report a case of CCOC affecting the mandible of a 39-year-old man. The tumor presented a biphasic pattern composed of clear cell nests intermingled with eosinophilic cells and separated by collagenous stroma. Immunoreactivity to cytokeratin (CK), specifically AE1/AE3 and CK 8, 14, 18, and 19 was found, as well as to epithelial membrane antigen (EMA). The tumor cells were negative for S100 protein, CK 13, vimentin, smooth muscle actin, laminin and type IV collagen. Low labeling indices for the proliferation markers Ki-67 and proliferating cell nuclear antigen and to p53 protein might predict a favorable prognosis for the lesion. A surgical resection was performed, followed by adjuvant radiotherapy. A 2-year follow-up has shown no signs of recurrence. The significance of histochemical and immunohistochemical resources in the correct diagnosis of CCOC is analyzed.

ERBB receptors in developing, dysplastic and malignant oral epithelia

Some oral squamous cell carcinomas (OSCCs) overexpress epidermal growth factor receptor (EGFR) but little is known about the receptor system overall during oral carcinogenesis. We studied all four ERBB receptors (EGFR, ERBB2-4) in developing (n=2), normal (n=7), dysplastic (n=23) and malignant (n=26) oral epithelia by means of immunohistochemistry. The investigations were supplemented by conducting reverse transcription-polymerase chain reactions in relation to 13 OSCC samples. All four ERBB receptors were detected in developing oral epithelium and, to a lesser degree, in mature oral epithelium. An increase in EGFR immunoreactivity was seen in 61% and 54% of dysplasias and OSCCs, respectively. The corresponding percentages for ERBB2 were 48 and 12, for ERBB3 48 and 43. ERBB4 nuclear staining was increased in 30% of dysplasias and 26% of OSCCs. Changes in ERBB receptor mRNA levels were not statistically significant. The results show that ERBB receptor profiles are specific to each tumour. Increased nuclear translocation of ERBB4 in some OSCCs may alter transcription of target genes and be associated with cancer progression. This information may be useful for clinicians as EGFR inhibitors are becoming treatment options in modern oncology.

Expression of integrin subunits alpha2, alpha3, alpha5, alphav, beta1, beta3 and beta4 in different histological types of ameloblastoma compared with dental germ, dental lamina and adult lining epithelium

OBJECTIVE

To analyze integrin expression and distribution in different histological types of ameloblastoma, compared with dental germ, dental lamina and adult lining epithelium.

MATERIALS AND METHODS

Three-micrometer sections from paraffin-embedded specimens were evaluated employing a streptavidin-biotin immunohistochemical method and anti-integrin alpha2, alpha3, alpha5, alphav, beta1, beta3 and beta4 antibodies.

RESULTS

All integrins were present in all specimens, exhibiting different patterns. In follicular ameloblastoma, the integrin staining was stronger in the periphery while integrin alpha2 was not present in the central cells. Acanthomatous ameloblastoma showed a similar pattern, with positive staining for integrins alpha3, alpha5, alphav, beta1 and beta4 in the metaplastic cells. In the unicystic, integrin staining was uniform except for integrins alpha5 and beta3 which showed weaker staining in the upper layers. In the plexiform ameloblastoma, dental germ and lamina integrin staining was uniform. In the adult lining epithelium, staining for integrins alpha2, alpha5 and beta4 was confined to the basal layer, while integrins alphav and beta3 were present in the basal and parabasal, with integrins alpha3 and beta1 in the upper layers.

CONCLUSION

Acanthomatous, follicular and unicystic ameloblastomas showed integrin staining patterns similar to the adult lining epithelium while the plexiform ameloblastoma was similar to the dental germ and lamina.

Cytokeratin expression in central mucoepidermoid carcinoma and glandular odontogenic cyst

Central mucoepidermoid carcinoma (MEC) is an entity whose origin is still controversial. Glandular odontogenic cyst (GOC) is a recently described lesion whose relationship to low-grade central MEC has been reported in the literature. Our aim was to assess the cytokeratin (CK) profile of central MEC and GOC, and compare the results with CK expression in salivary gland MEC and odontogenic cysts and tumors. Eighty-five cases, including 6 central MECs, 23 salivary gland MECs, 10 GOCs, 34 odontogenic cysts and 12 ameloblastomas, were studied through immunohistochemistry using eleven monoclonal anti-CK antibodies. All central MECs expressed CKs 5, 7, 8, 14, and 18 and all GOCs expressed CKs 5, 7, 8, 13, 14, and 19. Comparing CK expression from GOC and central MEC we found differences in CKs 18 (30% vs 100%) and 19 (100% vs 50%). Central MEC and GOC are probably distinct entities with CK profiles similar to lesions of glandular and odontogenic origins, respectively, and expression of CKs 18 and 19 could be useful in their differential diagnosis.

Cytokeratins in epithelia of odontogenic neoplasms

Neoplasms and tumours related to the odontogenic apparatus may be composed only of epithelial tissue or epithelial tissue associated with odontogenic ectomesenchyme. The immunohistochemical detection of different cytokeratins (CKs) polypeptides and vimentin has made it easier to explain the histogenesis of many epithelial diseases. The present study aimed to describe the immunohistochemical expression of cytokeratins 7, 8, 10, 13, 14, 18, 19 and vimentin in the epithelial components of the dental germ and of five types of odontogenic tumours. The results were compared and histogenesis discussed. All cells of the dental germ were positive for CK14, except for the preameloblasts and secreting ameloblasts, in which CK14 was gradually replaced by CK19. CK7 was especially expressed in the cells of the Hertwig root sheath and the stellate reticulum. The dental lamina was the only structure to express CK13. The reduced epithelium of the enamel organ contained CK14 and occasionally CK13. Cells similar to the stellate reticulum, present in the ameloblastoma and in the ameloblastic fibroma, were positive for CK13, which indicates a nature other than that of the stellate reticulum of the normal dental germ. The expression of CK14 and the ultrastructural aspects of the adenomatoid odontogenic tumour probably indicated its origin in the reduced dental epithelium. Calcifying odontogenic epithelial tumour is thought to be composed of primordial cells due to the expression of vimentin. Odontomas exhibited an immunohistochemical profile similar to that of the dental germ. In conclusion, the typical IF of odontogenic epithelium was CK14, while CK8, 10 and 18 were absent. Cytokeratins 13 and 19 labelled squamous differentiation or epithelial cells near the surface epithelium, and CK7 had variable expression.

Cytokeratin expression patterns in jaw cyst linings with metaplastic epithelium

BACKGROUND

Cytokeratin (CK) expression patterns have been studied in numerous intact and diseased oral tissues. However, CK expression in metaplastic squamous cells has not been explored in depth and the origin of metaplastic epithelial linings of the jaw cysts has not been sufficiently investigated.

METHODS

We examined CK expression in 46 postoperative maxillary cysts (POMCs) which were lined with pseudostratified columnar cells only, columnar and squamous cells, and squamous cells only, in 13, 30 and 3 cases, respectively.

RESULTS

The expression of CK8, CK13 and CK18 were observed in 39, 9 and all 43 of the columnar epithelial linings, respectively. Metaplastic squamous epithelia expressed more CK13, and less CK18 and CK8. Of the 33 metaplastic linings, 24 expressed CK8, 23 CK13 and 26 linings expressed CK18. The patterns of expression of CK13 and CK18 observed were CK18(+)-CK13(-) in 10 metaplastic linings, CK18(+)-CK13(+) in 16, and CK18(-)-CK13(+) in 7. The expression of CK13- and CK18-mRNA was generally correlated with level of protein expressed. CK18-mRNA expression was observed by in situ hybridization, not only in the 26 metaplastic linings which were positive for CK18 protein, but also in five of the seven metaplastic linings which did not express CK18 protein. In addition, RT-PCR revealed an expression of CK18-mRNA in all metaplastic squamous linings, although the expression level was weaker than that in the columnar epithelial linings. The CK13-mRNA was expressed inversely to the CK18-mRNA.

CONCLUSIONS

These results indicate that CK18-mRNA is preserved through metaplasia, although the protein expression decreased. Metaplastic squamous cells differentiate with a decrease of CK18 and an increase of CK13 expression.

Cytokeratins expression of constituting cells in ameloblastoma

The purposes of this study were to investigate the distribution of cytokeratins in the different tissue types of ameloblastoma and to discuss the histogenesis of this tumor. CK19 and CK8, which are markers for odontogenic epithelium, reacted positively to the constituting cells in all types of ameloblastoma. This suggests that all types of ameloblastoma derive from odontogenic epithelium. However, the desmoplastic type diminished the odontogenic characteristics because the basal cells are negative to CK19. Immunoreactions of five kinds of cytokeratin revealed similar results in plexiform, follicular, acanthomatous, and granular cell types. The plexiform type is probably the original type of ameloblastoma; the other types have the characteristics of squamous epithelium, and the follicular, acanthomatous, and granular cell types can develop due to the differentiation of cells of the plexiform type into squamous epithelium.

Expression of cytokeratins (CKs) 8, 13 and 18 and their mRNA in epithelial linings of radicular cysts: implication for the same CK profiles as nasal columnar epithelium in squamous epithelial lining

OBJECTIVE

Our objective was to specify cytokeratin (CK) patterns in lining epithelia of radicular cysts which are sometime lined with ciliated columnar epithelia as seen in the nasal epithelia.

MATERIALS AND METHODS

We examined the CK expression in 52 radicular cysts obtained from 32 maxillary and 20 mandibular lesions and investigated CK-mRNA expression using in situ hybridization in 24 maxillary and 13 mandibular cysts and reverse transcription-polymerase chain reaction (RT-PCR) in 24 maxillary cysts.

RESULTS

Of the maxillary cysts, 20, 29 and 19 squamous epithelial linings were positive for CK8, CK13 and CK18, respectively; of the mandibular cysts, 10, 20 and 11 linings were positive for these CKs, respectively. The expression patterns of CK18(+)-CK13(-), CK18(+)-CK13(+) and CK18(-)-CK13(+) were observed in 3, 16 and 13 linings of the maxillary cysts and 0, 11 and 9 linings of the mandibular cysts, respectively. In situ hybridization revealed the expression of CK18-mRNA in 9 and 4 linings of 24 maxillary and 13 mandibular cysts examined, respectively. With RT-PCR, we explored that both CK18- and CK13-mRNA were expressed not only in the normal nasal and gingival epithelia but also in the examined maxillary cyst linings although their expression levels differed correlating with the difference in CK staining.

CONCLUSION

It is concluded that CK13- and CK18-mRNA are constitutively expressed in columnar and squamous epithelial cells, respectively, and that the variant CK expression patterns with CK18-mRNA expression in maxillary radicular cysts are indicative of the possibility of phenotypic transformation in the cyst linings.

Clear cell odontogenic carcinoma: a clinicopathologic and immunocytochemical study of 5 cases

CONTEXT

Odontogenic tumor composed predominantly of clear cells is a rare neoplasm of the jaws that was initially designated as clear cell odontogenic tumor. Subsequent reports in the literature, however, all have indicated that this tumor exhibits an aggressive behavior characterized by infiltrative local growth, recurrence, or metastases.

OBJECTIVE

To ascertain the clinicomorphologic features and biologic behavior of this tumor group, we present 5 additional cases using the term clear cell odontogenic carcinoma.

DESIGN

Histologic and immunohistochemical examinations were performed on clear cell odontogenic carcinomas from 5 patients. Clinical and follow-up data were recorded, and the literature was reviewed.

RESULTS

The patients were 1 man and 4 women with an average age of 42.4 years at diagnosis. Three tumors occurred in the mandible and the other 2 in the maxilla. Four of the 5 cases occurred in the anterior or premolar areas of the jaws, appearing as poorly marginated radiolucencies. All cases consisted of islands and sheets of large clear cells and small basaloid cells with scanty eosinophilic cytoplasm, which were separated by thin, mature, fibrous septae. The tumors were unencapsulated and showed aggressive infiltration of the surrounding muscle and perineural tissues. Most of the clear cells contained cytoplasmic glycogen. Immunocytochemically, the tumor cells were positive for pan-keratin, cytokeratin 19, and epithelial membrane antigen, but were negative for vimentin, S100 protein, desmin, smooth muscle actin, human melanoma antigen (HMB-45), and alpha(1)-antichymotrypsin. Follow-up data showed 4 of 5 patients to have multiple local recurrences, and 1 of these 4 had submandibular lymph node metastasis and a fatal outcome due to uncontrollable tumor growth.

CONCLUSION

These results suggest that odontogenic clear cell neoplasms are at least low-grade malignancies and should be classified as carcinomas.

Immunohistochemical expression of neural tissue markers (neuron-specific enolase, glial fibrillary acidic protein, S100 protein) in ameloblastic fibrodentinoma: a comparative study with ameloblastic fibroma

Formalin-fixed paraffin-embedded sections of three cases of ameloblastic fibrodentinoma (AFD) were studied by the avidin-biotin-peroxidase complex method using antibodies against neuron-specific enolase (NSE), glial fibrillary acidic protein (GFAP) and S100 protein and the results were compared with those in ameloblastic fibroma (AF). A striking histopathological characteristic of AFD was the formation of abortive dentin with various degrees of maturation at the epithelial-mesenchymal tissue interface. Central cells of enamel organ-like epithelia with various stages of abortive dentin induction in AFD were generally positive for NSE. Dental lamina-like epithelial cells also showed positive staining in some areas. No cells were positive for NSE in AF. Positive staining for GFAP was observed in the juxta-epithelial mesenchymal tissue of the formation stage of immature dentin with various numbers of entrapped cells in AFD, but GFAP staining was negative in other mesenchymal and epithelial tissues at other stages. In AF, no GFAP-positive cells were found. There were a few S100 protein-positive cells found in the foci of epithelial components in both AFD and AF. Mesenchymal cells showing a dendritic or spindle shape were positive for S100 protein in some areas of AFD and AF. Although such cells in the mesenchymal component of pigmented AFD were more numerous than in non-pigmented AFD and AF, their distribution pattern in the former condition was basically similar to that in the latter. Although the present results, obtained from conventional immunohistochemical procedures, do not directly reflect the expression of neural crest-derived cells in the dentinogenesis of AFD, such results do not disprove the possibility of the expression of neural proteins probably related to neural crest-derived cells in dentinogenesis under certain pathologic conditions in odontogenic mixed tumors. Such a phenomenon may also occur during dentinogenesis in other odontogenic mixed tumors and in normal tooth differentiation, but at an undetectable level.

Calretinin expression in ameloblastomas

AIMS

Calretinin is a 29-kDa calcium-binding protein which is expressed in the central and peripheral nervous systems as well as in many other normal and pathological human tissues. The objective of this study was to determine whether calretinin was expressed in the epithelium of ameloblastomas.

METHODS AND RESULTS

Twenty-seven cases of unicystic ameloblastoma and 31 cases of solid and multicystic ameloblastoma were studied. Five-micron sections were immunohistochemically stained using either antiserum 7696 from Swant, or antiserum 18-0211 from Zymed with a standard ABC method. The results were identical with the two antisera. Positive staining was seen in 22 cases (81.5%) of unicystic ameloblastomas. This generally consisted of diffuse, intense nuclear and cytoplasmic staining of several cell layers of the more superficial cells both in the characteristic and nondescript areas of the cyst linings. In the solid and multicystic ameloblastomas, staining occurred in 29 (93. 5%) of the cases. The staining was almost always restricted to the stellate reticulum-like epithelium, was generally intense and diffuse in distribution. Areas of squamous metaplasia stained particularly intensely as did the cells surrounding micro- and macro-cysts. In both groups of lesions, most of the cases that did not stain were intensely inflamed.

CONCLUSIONS

The biological significance of calretinin expression in ameloblastomas is not known and its use as a distinctive, specific immunohistochemical marker for ameloblastic tissues remains to be confirmed. However, the results of this study raise the possibility that calretinin may be an important diagnostic aid in the differential diagnosis of cystic and solid ameloblastic tumours.

The impact of molecular genetics on oral health paradigms

As a result of our increased understanding of the human genome, and the functional interrelationships of gene products with each other and with the environment, it is becoming increasingly evident that many human diseases are influenced by heritable alterations in the structure or function of genes. Significant advances in research methods and newly emerging partnerships between private and public sector interests are creating new possibilities for utilization of genetic information for the diagnosis and treatment of human diseases. The availability and application of genetic information to the understanding of normal and abnormal human growth and development are fundamentally changing the way we approach the study of human diseases. As a result, the issues and principles of medical genetics are coming to bear across all disciplines of health care. In this review, we discuss some of the potential applications of human molecular genetics for the diagnosis and treatment of oral diseases. This discussion is presented in the context of the ongoing technological advances and conceptual changes that are occurring in the field of medical genetics. To realize the promise of this new molecular genetics, we must be prepared to foresee the possibilities and to incorporate these newly emergent technologies into the evolving discipline of dentistry. By using examples of human conditions, we illustrate the broad application of this emerging technology to the study of simple as well as complex genetic diseases. Throughout this paper, we will use the following terminology: Penetrance--In a population, defined as the proportion of individuals possessing a disease-causing genotype who express the disease phenotype. When this proportion is less than 100%, the disease is said to have reduced or incomplete penetrance. Polymerase chain reaction (PCR)--A technique for amplifying a large number of copies of a specific DNA sequence flanked by two oligonucleotide primers. The DNA is alternately heated and cooled in the presence of DNA polymerase and free nucleotides, so that the specified DNA segment is denatured, hybridized with primers, and extended by DNA polymerase. MIM--Mendelian Inheritance in Man catalogue number from V. McKusick's Mendelian Inheritance in man (OMIM, 1998).

An immunohistochemical study of keratin expression in ameloblastoma from a Kenyan population

OBJECTIVES

Ameloblastomas appear to exhibit biological heterogeneity and, except in the case of malignancy, histological appearances that do not always allow their behaviour to be predicted. The aim of this study was to assess keratin expression in African ameloblastomas and to correlate this with their clinical and histological features.

MATERIALS AND METHODS

Expression of simple keratins 7, 8, 18 and 19; cornification keratins 1 and 10; basal and differentiation keratins 5 and 14 and hyperproliferation-related keratins 6 and 16 in 14-39 cases of ameloblastoma was assessed by immunohistochemical methods.

RESULTS

There was patchy expression of keratin 7 in the suprabasal and stellate reticulum-like cells in some cases. All cases showed similar weak expression for keratins 8 and 18 in suprabasal and stellate reticulum-like cells but none showed keratin 1 or 10 expression. There was intense expression of keratins 5, 14 and 19 by all tumour cells suggesting that they may retain basal cell characteristics with a potential for proliferation. No consistent relationship was seen between histological types and keratin expression pattern. However, keratins 6 and 16, expressed by suprabasal and stellate reticulum-like cells, showed a marked variation within and between cases, with the highest levels of expression in squamous strands.

CONCLUSIONS

We propose that squamous strands may represent the sites of most active growth within individual tumours and expression of keratins 6, 16 and 19 may be predictors of rapid growth. There is a need for further investigation of this in longitudinal clinical studies.

Aberrant gene expression in epithelial cells of mixed odontogenic tumors

Comparative investigations of odontogenic cells in normally forming teeth and tumors may provide insights into the mechanisms of the differentiation process. The present study is devoted to late phenotypic markers of ameloblast and odontoblast cells, i.e., proteins involved in biomineralization. The in situ expression of amelogenins, keratins, collagens type III and IV, vimentin, fibronectin, osteonectin, and osteocalcin was performed on normal and tumor odontogenic human cells. The pattern of protein expression showed some similarities between ameloblasts and odontoblasts present in normally developing human teeth and cells present in neoplastic tissues of ameloblastic fibroma, ameloblastic fibro-odontomas, and complex odontomas. Amelogenins (for ameloblasts) and osteocalcin (for odontoblasts) were detected in cells with well-organized enamel and dentin, respectively. In contrast, "mixed" cells located in epithelial zones of mixed odontogenic tumors co-expressed amelogenins and osteocalcin, as shown by immunostaining. The presence of osteocalcin transcripts was also demonstrated by in situ hybridization in these cells. Keratins and vimentin were detected in the same epithelial zones. Tumor epithelial cells were associated with various amounts of polymorphic matrix (amelogenin- and osteocalcin-immunoreactive), depending on the types of mixed tumors. No osteocalcin labeling was found in epithelial tumors. This study confirms that the differentiation of normal and tumor odontogenic cells is accompanied by the expression of some common molecules. Furthermore, the gene products present in normal mesenchymal cells were also shown in odontogenic tumor epithelium. These data may be related to a tumor-specific overexpression of the corresponding genes transcribed at an undetectable level during normal development and/or to an epithelial-mesenchymal transition proposed to occur during normal root formation. A plausible explanation for the results is that the odontogenic tumor epithelial cells are recapitulating genetic programs expressed during normal odontogenesis, but the tumor cells demonstrate abnormal expression patterns for these genes.

Clear cell odontogenic tumor in the mandible: report of a case with an immunohistochemical study of epithelial cell markers

A rare case of clear cell odontogenic tumor is presented with an immunohistochemical study using epithelial cell markers. A 35-year-old Japanese man was admitted with a complaint of painless swelling in the anterior region of his mandible. Radiological examination showed a relatively well-defined multilocular radiolucency with root resorption of the adjacent teeth. Despite a subtotal mandibulectomy, the tumor recurred three times. Histologically, the tumor was composed of proliferating clear cells and infiltrated through the cancellous bone. Histochemical and ultrastructural analyses detected cytoplasmic glycogen granules in the clear cells. They showed immunoreactivities for cytokeratin 8, 13 and 19, filaggrin and anti-ameloblastoma antibodies, suggesting an odontogenic epithelial origin.

Establishment of ameloblastoma cell line, AM-1

Ameloblastomas are slowly growing, locally invasive neoplasms with a potentially destructive behaviour. The molecular mechanisms that regulate the cell growth and invasion of ameloblastoma cells are unknown. Because ameloblastoma cells placed in culture have a very limited lifespan, the establishment of immortalized clones of ameloblastoma cells would aid its study. We produced an immortalized ameloblastoma cell line (AM-1) using human papillomavirus type-16. This cell line maintains epithelial cell morphology and expresses cytokeratins K8, K14, K18, K19. Furthermore, bcl-2 protein, which prevents apoptosis, is expressed. We investigated the behaviour of these cells on a collagen matrix in vitro. These cells grew in a monolayer over foci of collagen degradation and could invade the collagen gel at such sites. Since the behavior of cell line AM-1 mimics the behavior of ameloblastoma in vivo, it may be a valuable model for the study of these neoplasms.

The relationship of adamantinomatous craniopharyngioma to ghost cell ameloblastoma of the jaws: a histopathologic and immunohistochemical study

The objective of this investigation was to study the relationship of the ghost cell ameloblastoma (GCA), which is a form of type II calcifying odontogenic cyst (COC), to the adamantinomatous craniopharyngioma (ACP). H&E sections of 26 examples of ACP were compared to three cases of GCA and to the reported microscopic features of that tumor. Clinical records of the ACPs were studied to determine their biologic behavior compared to that of the ameloblastomas. Immunohistochemical studies of nine examples of ACP were performed for KL1 (high mol.wt cytokeratins), 5D3 (low mol.wt cytokeratins) and involucrin (characteristic of terminally differentiated keratinocytes) using the peroxidase-antiperoxidase method. The results were compared with those reported for COC and ameloblastoma. ACP and GCA exhibited similar microscopic features, including pre-ameloblasts, tissue resembling stellate reticulum, ghost cells and calcifications; both tumors grew slowly and were invasive. ACP and COC, and by interpolation GCA, exhibited similar features with all three antibodies. The ghost cells did not exhibit any immunoreactivity but the adjacent cells stained positively for involucrin. The immunological features of ACP were similar to those reported in ameloblastomas for squamous differentiation. However, because of their rarity, no ameloblastomas exhibiting keratinization, including ghost cells, have yet been studied with these antibodies. We conclude that ACP and GCA are homologous lesions.

Features of odontogenesis and expression of cytokeratins and tenascin-C in three cases of extraosseous and intraosseous calcifying odontogenic cyst

To characterize further the nature of calcifying odontogenic cyst (COC), we studied histologically and immunohistochemically an extraosseous and two intraosseous lesions. The extraosseous COC was in continuity with the stratified squamous epithelium of the alveolar mucosa. Immunostaining with monoclonal antibodies showed reactivity of both low- and high-molecular-weight cytokeratins, the degree of coexpression decreasing with the increasing morphological diversity of the cyst/tumour epithelium. Staining for the matrix glycoprotein tenascin-C was seen not only in the connective tissue, where its distribution patterns corresponded to the stage of hard tissue formation, but also in epithelial elements. The staining patterns were analogous to those described during normal tooth formation. Both the morphological characteristics and expression patterns of the various cytokeratin types and tenascin-C implied that COC represents a pathological counterpart of normal odontogenesis. In the case of the extraosseous COC, the correspondence could be traced back to early stages of tooth development.

Characterization of novel monoclonal antibodies raised against formalin-fixed, paraffin-embedded human ameloblastoma

To obtain monoclonal antibodies reactive with odontogenic but not other types of epithelium, mice were immunized with homogenates of fixed ameloblastoma tissues, and monoclonal antibodies Y4 and M11 were produced. Y4 reacted immunohistochemically with odontogenic epithelial components but not with those of squamous differentiation, while M11 reacted with odontogenic epithelial components and a part of keratotic epithelial tissues. Immunoglobulin isotypes of both antibodies were IgM as determined by Ouchterlony immunodiffusion and enzyme-linked immunosorbent assays. Western blotting revealed that the antigen recognized by Y4 had a molecular mass of approximately 66 kDa; however, the antigen reactive with M11 was not identified by Western blotting in spite of various attempts in changing reaction conditions. These antibodies may be beneficial to histological analyses of odontogenic tissues and their related lesions.

Immunohistochemical observations on a possible ameloblastic fibro-odontoma

An ameloblastic fibro-odontoma which occurred in the mandible of a 3-year-old Japanese boy is reported together with immunohistochemical findings. Histologically, the tumor consisted of an ameloblastic fibroma-like area and some typical complex odontoma-like areas. The epithelial islands in the ameloblastic fibroma-like area showed different developmental stages of the epithelial-connective tissue interface. Immunohistochemical examination revealed that all epithelial components in the ameloblastic fibroma-like area showed expression of CK 8, CKs 13, 16, CK 14, CK 18 and CK 19, and coexpression of these cytokeratins and vimentin. These findings suggest that even the epithelial component without obvious epithelial-mesenchymal induction showed the final cell differentiation of the enamel organ with the potential for epithelial-mesenchymal induction.

Structural and compositional alteration of tooth enamel in hereditary epidermolysis bullosa

Epidermolysis bullosa (EB) is a group of conditions characterized by basement membrane and cellular defects that result in skin fragility and variable extra-cutaneous involvement. The teeth can be severely affected with marked enamel malformations. The purpose of this study was to characterize the structure and composition of teeth from individuals representing the major EB groups (EB simplex, dystrophic EB and junctional EB). Teeth were examined from 28 individuals with EB and 10 healthy people unaffected by EB. Teeth from individuals with junctional EB had marked enamel hypoplasia with varying abnormalities in the enamel structure. Minor structural defects of enamel, including areas of surface pitting, were seen in the other EB types. Although there was a slight reduction (approximately 10%) in the enamel mineral content in several dystrophic EB and junctional EB teeth, the mean mineral content was similar for all EB enamel types and normal enamel. This study shows that while individuals with junctional EB have marked alteration of the enamel structure, the composition may be normal to only mildly altered. Laminin-5, the molecular defect in junctional EB, is associated primarily with alteration in the amount and/or structure of enamel while the mineralization process appears relatively intact. The marked enamel hypoplasia in this EB type suggests that laminin-5 plays an important role in the secretory phase of enamel development.

Maintenance of cell-type-specific cytoskeletal character in epithelial cells out of epithelial context: cytokeratins and other cytoskeletal proteins in the rests of Malassez of the periodontal ligament

We have determined the patterns of synthesis of cytokeratins and other epithelial marker proteins in the "rests of Malassez" of the periodontium of rabbits and humans, by immunofluorescence microscopy of cryosections prepared from fixed and decalcified rabbit teeth with attached ligament or from manually isolated human periodontal ligaments. Proteins of the major cell structures characterizing epithelial differentiation are present in Malassez cells: a complex set of cytokeratins as well as desmosomal, hemidesmosomal and basal lamina proteins. In addition, we have shown these cytoskeletal and extracellular matrix structures by electron microscopy. The cytokeratin complement of Malassez cells was found to be highly complex, as 8 of the total of 20 known epithelial cytokeratins were detected (nos. 5, 7, 8, 14, 15, 17, 18, 19). This pattern, together with the presence of the desmosomal cadherins Dsg2 and Dsc2 and the cytoplasmic desmosome plaque-associated protein plakophilin 1, indicates that the cells of the rests of Malassez are derived from the basal cell layer of a stratified squamous epithelium rather than from simple epithelial or neuroendocrine epithelial cells. Our observations show that Malassez cells retain the major characteristics of epithelial cells throughout their differentiation from the root sheath epithelium into the rests of Malassez, even though the surface location and the polar tissue architecture that typify epithelial are lost during this process. From this study we further conclude that the specific cytoskeletal complement of the Malassez cells represents an intrinsic gene expression program that neither depends on nor causes the formation of a stratified epithelium. We also compare the specific cytoskeletal features of Malassez cells with those of other persisting epithelial residues and discuss the potential value of these findings in relation to the histogenesis and diagnostic classification of dental and periodontal cysts and tumors.

Ameloblastoma: biological profile of 3677 cases

Available literature on ameloblastoma of the jaw was reviewed, including publications from 1960 to 1993, and compared to the latest larger review, published by Small and Waldron in 1955. The average age of patients with ameloblastoma is 36 years. In developing countries ameloblastomas occur in younger patients. Men and women are equally affected. Women are 4 years younger than men when ameloblastomas first occur, and the tumours appear to be larger in females. Dominant clinical symptoms such as painless swelling and slow growth are non-characteristic. The ratio of ameloblastoma of the mandible to maxilla is 5 to 1. Ameloblastomas of the mandible occur 12 years earlier than those of the maxilla. Ameloblastomas occur most frequently in the molar region of the mandible. In Blacks, ameloblastomas occur more frequently in the anterior region of the jaws. Radiologically, 50% of ameloblastomas appear as multilocular radiolucent lesions with sharp delineation. Histologically, one-third are plexiform, one-third follicular; other variants such as acanthomatous ameloblastoma occur in older patients. Two percent of ameloblastomas are peripheral tumours. Unicystic ameloblastomas occurring in younger patients have been found in 6%. Detailed data on 345 patients with ameloblastoma were evaluated for clarification of therapeutic approaches. Chemotherapy and radiation seem to be contraindicated. Ameloblastomas of the maxilla should be treated as radically as possible, ameloblastomas of the mandible should also be treated radically. However, ameloblastomas which radiologically appear as unilocular lesions may be treated conservatively (enucleation, curettage), whenever all areas of the cystic lumen are controllable intraoperatively. Unicystic ameloblastomas occurring in patients 15 years younger than those with multisystic ameloblastoma may be treated conservatively except in cases with invasion of epithelium into the cyst wall. Different recurrence rates have been found for histological variants of the ameloblastoma. Follicular ameloblastomas appear to recur more often than the plexiform type. Unicystic ameloblastomas reveal lower recurrence rates than "non-unicystic" ameloblastomas. The peripheral type of ameloblastoma may be excised, since conservative therapy results in low recurrence rates. Postoperative follow-up is most important in the therapy of ameloblastoma, because more than 50% of all recurrences occur within 5 years postoperatively.

An immunohistochemical study of odontogenic mixed tumours

Five cases of odontogenic mixed tumour comprising of an ameloblastic fibroma, an adenomatoid odontogenic tumour, an odonto-ameloblastoma and two ameloblastic fibro-odontomas were immunohistochemically investigated. Odontogenic epithelial cells were fully positive for cytokeratin detected by antibody KL-1, although there were some differences in its intensity. In contrast, for tenascin, only immature dental papilla-like mesenchymal tissue, especially around the dental lamina-like odontogenic epithelium, was positive, while the myxomatous area and connective tissue were negative. Positive vimentin staining was observed in some areas of immature dental papilla-like cells as well as the basement membrane of odontogenic epithelium in the ameloblastic fibroma, suggesting that this tumour had developed at the early stage of tooth formation. Proliferating nuclear cell antigen-positive cells were generally rarely seen, but were frequently observed in epithelial cells of the ameloblastic fibroma and odonto-ameloblastoma. These observations suggest that tumour cells in each odontogenic mixed tumour possess characteristic proteins associated with proliferation potential and that ameloblastic fibroma and odonto-ameloblastoma have higher proliferation potential among the tumours examined.

A survey of epithelial odontogenic tumors and cysts in dogs and cats

A retrospective histologic study of 12 canine and eight feline epithelial odontogenic tumors and cysts was conducted from oral masses (n = 3,917) obtained between 1980 and 1990. No sex or breed predilection was identified. Ameloblastoma was observed in two dogs (case Nos. 1, 2) 6 and 8 months of age. Calcifying epithelial odontogenic tumors were seen in a dog (case No. 3) and in two cats (case Nos. 4, 5) between 8 and 16 years of age. Ameloblastic fibroma (or fibroameloblastoma) was observed in cats (case Nos. 6-10) only. Inductive fibroameloblastoma was observed in four cats (case Nos. 6-9) up to 1 year of age, whereas ameloblastic fibroma was seen in a 14-year-old cat (case No. 10). A single ameloblastic odontoma was identified in a 20-month-old dog (case No. 11). Two complex odontomas occurred in a 6-month-old (case No. 12) and a 4-year-old (case No. 13) dog. Odontogenic cysts were identified in five dogs (case Nos. 14-18) aged 4.5 months to 16 years and in a 1-year-old cat (case No. 19) and have not been previously reported in these species. These cysts were lined by a stratified epithelium reminiscent of the appearance of ameloblastic epithelium. An odontogenic keratocyst with prominent central parakeratotic keratinization was identified in one 9-year-old female dog (case No. 20). Almost all epithelial odontogenic tumors were circumscribed, benign tumors that warranted a good prognosis for survival, although local recurrence may have followed (or may follow) incomplete excision. Calcifying epithelial odontogenic tumors may be locally invasive. Of six odontogenic cysts (case Nos. 14-19), two (case Nos. 15, 18) gave rise to basi-squamous carcinomas. The classification and behavior of epithelial odontogenic tumors and cysts in human beings, dogs, and cats are discussed.

Expression of different cytokeratin subclasses in human chordoma

A detailed immunohistochemical characterization of different cytokeratin subclasses was performed on frozen tumour tissue from three classical chordomas. Simple epithelium cytokeratins Nos 8, 18, and 19 were detected in all tumour cells while cytokeratin No. 7 was not found. Cytokeratins characteristic of squamous differentiation, including keratinization, were generally lacking, with the exception of the varying expression of cytokeratin No. 4. Vimentin was found in all the tumours, while they lacked desmin immunoreactivity. The present study indicates the co-expression of vimentin and cytokeratins, predominantly of the simple epithelium type. In addition, chordoma cells have the ability to express cytokeratins characteristic of squamous differentiation. This finding corresponds well to the electron microscopic findings of tonofilament bundles ending in well-developed desmosomes.

Immunohistochemical study of jaw cysts: different existence of keratins in odontogenic and non-odontogenic epithelial linings

Keratins and secretory component (SC) were immunohistochemically examined in fresh tissue samples from 45 odontogenic and 35 non-odontogenic cysts. Lining epithelia of almost all cases contained keratins which reacted with polyclonal antibodies (Dako, Bio-Science), and no difference could be found between the two groups of lesions. By staining with two monoclonal antibodies against keratins, i.e., RGE53 (Bio-Science) and RKSE60 (Bio-Science), it was revealed that the epithelia of non-odontogenic cysts, which were columnar epithelium in most cases, had fully and positively reacted with RGE53, while none of the cases was positive for RKSE60. In contrast, the squamous linings of odontogenic cysts except for two cases did not react with RGE53, and few cases possessed RKSE60-reactive keratin. SC was also contradictory. All non-odontogenic cysts exhibited SC. Regarding each pair of non-odontogenic and odontogenic cysts covered with RGE53 and SC-positive, and RKSE60-negative squamous epithelium, it seemed reasonable from the staining results to conclude that the squamous linings were metaplastic from the columnar epithelium. Based on the results, concomitant examinations of SC with keratins will be helpful in deciding the epithelial derivation of jaw cysts.