Cartilage-specific matrix protein chondromodulin-I is associated with chondroid formation in salivary pleomorphic adenomas: immunohistochemical analysis

Chondromodulin-I (ChM-I) is a novel cartilage-specific matrix protein. In the growth plates of the long bones, ChM-I was shown to be expressed in mature to upper hypertrophic chondrocytes, and to be deposited in the cartilage matrix. As ChM-I strongly inhibits angiogenesis, cartilage is avascular. Also, ChM-I has bifunctional activity against chondrocyte proliferation. On the other hand, pleomorphic adenomas of the salivary glands frequently have chondroid elements. To elucidate the relationship between chondroid formation and hypovascularity in salivary pleomorphic adenomas, we immunohistochemically examined the expression and localization of ChM-I in 35 cases of this tumor. ChM-I was immunolocalized to the lacunae in the chondroid elements of pleomorphic adenomas (100%). Type II collagen and aggrecan were immunolocalized throughout the matrix around lacuna cells of the chondroid element (100%, 91.7%), and ChM-I was infrequently immunolocalized to the spindle-shaped myoepithelial cells in the myxoid element (37.5%). Fibroblast growth factor-2 was strongly immunolocalized to the lacuna cells in the chondroid element (100%), among the neoplastic myoepithelial cells in the myxoid elements (96.9%), and on the basement membranes around the solid nests of neoplastic myoepithelial cells (71.4%). Although CD34 is a marker of endothelial cells, CD34 was expressed in the endothelial cells in only a few areas around the epithelial elements and in the fibrous element of pleomorphic adenomas. No signals for CD34 were observed in chondroid elements in pleomorphic adenomas (P < 0.001), but a few signals were seen in the myxoid elements (P < 0.05). These findings suggested that lacuna cells and neoplastic myoepithelial cells expressed ChM-I, and that this molecule may play an important role in hypovascularity and chondroid differentiation in pleomorphic adenoma. In conclusion, pleomorphic adenoma expressed ChM-I, which is involved in hypovascularity and chondroid formation in this type of tumor.     

Expression and localization of cartilage-specific matrix protein chondromodulin-I mRNA in salivary pleomorphic adenomas

Pleomorphic adenoma is the most common epithelial tumor in the salivary glands. This tumor frequently exhibits mesenchyme-like components, including myxoid or chondroid areas. Recently, using immunohistochemical techniques, we reported that cartilage-specific matrix protein, chondromodulin-I (ChM-I), was deposited on the inter-territorial matrix of the chondroid area in salivary pleomorphic adenomas and that ChM-I, which is also a strong angio-inhibitory factor, plays an important role in the avascular nature of the chondroid area and the chondroid formation in this type of tumor. To elucidate which cells express ChM-I mRNA in pleomorphic adenomas, we examined the expression and localization of ChM-I mRNA in this type of tumor using an in situ hybridization technique. Immunoreactivity for ChM-I was observed in the inter-territorial matrix of the chondroid area, especially around the lacunae, and in the cytoplasm of neoplastic myoepithelial cells of the myxoid element of pleomorphic adenomas. On in situ hybridization analysis, strong signals for ChM-I mRNA were detected in the cytoplasm of the lacuna cells of the chondroid element, and moderate to marked signals were observed in the cytoplasm of the neoplastic myoepithelial cells of the myxoid element. Signals for ChM-I mRNA were also seen in the cytoplasm of the spindle-shaped neoplastic myoepithelial cells in the transitional areas between the myxoid and chondroid elements of this tumor. Signals for ChM-I mRNA were not seen in the inner ductal cells or the fibrous element. These findings indicate that lacuna cells and neoplastic myoepithelial cells express ChM-I mRNA and that mature ChM-I, which lacuna cells and neoplastic myoepithelial cells translate, is deposited in the chondroid matrix of pleomorphic adenomas. In conclusion, lacuna cells and neoplastic myoepithelial cells express ChM-I mRNA ectopically in pleomorphic adenoma, and this plays an important role in chondroid formation and hypovascularity in this type of tumor.     

Lumican expression is associated with the formation of mesenchyme-like elements in salivary pleomorphic adenomas

Pleomorphic adenomas are the most common salivary gland tumour. Although this tumour is considered to be of epithelial origin, it contains 'mesenchyme'-like elements histologically. Lumican is a keratan sulphate proteoglycan that belongs to the small leucine-rich repeat (LRR) proteoglycans and has been reported to be associated with cartilage formation. These findings suggest that lumican expression may be related to the chondroid component in pleomorphic adenomas. To investigate this hypothesis, the present study investigated the expression and localization of lumican in 20 normal human salivary glands and 35 pleomorphic adenomas. Firstly, immunohistochemistry for lumican was performed with pepsin pretreatment. In normal salivary glands, lumican was deposited in the periductal regions. In pleomorphic adenomas, it was predominantly deposited in the hyaline (100%) and fibrous areas (89.4%). In 16 tumours (66.7%), lumican was also deposited in the chondroid areas. Without pepsin pretreatment, lumican was identified in myoepithelial cells in myxoid areas, lacuna cells in chondroid areas, and in the cytoplasm of inner ductal cells. In situ hybridization revealed lumican mRNA expression mainly in the inner cells, the neoplastic myoepithelial cells, and the lacuna cells. These results suggest that lumican is associated with the formation of 'mesenchyme'-like structures in pleomorphic adenomas. In conclusion, normal salivary glands express lumican, which appears to be related to stromal maintenance, and pleomorphic adenomas express lumican mRNA and protein, which may play important roles in the formation of 'mesenchyme'-like areas in this type of tumour.     

Immunohistochemical localization of the bone morphogenetic protein-6 in salivary pleomorphic adenomas

Salivary pleomorphic adenomas are often associated with chondroid tissue formation. We have found that bone morphogenetic proteins (BMP), especially BMP-2, may play an important role in ectopic chondrogenesis in this tumor. Bone morphogenetic protein-6 was reported to be related to the osteogenic metastasis of prostatic carcinomas. The relationship between BMP-6 expression and chondroid tissue formation is investigated. Twenty-three pleomorphic adenomas were examined immunohistochemically. The overexpression of BMP-6 was observed in 10 pleomorphic adenomas of the major salivary glands (43. 5%), and no evidence of BMP-6 expression in any of the nine pleomorphic adenomas of the palate. Bone morphogenetic protein-6 was immunolocalized in the lacuna cells of the chondroid tissue, in which type II collagen was localized. Bone morphogenetic protein-6 was expressed in inner ductal cells of the tubulo-glandular structures in the pleomorphic adenomas. This finding indicates that BMP-6 may be associated with the differentiation of inner ductal cells. Bone morphogenetic protein-6 was expressed weakly in neoplastic myoepithelial cells in the myxoid areas, which may be related to the production of extracellular matrices. Bone morphogenetic protein-6 has a role in chondroid formation, and also tubulo-glandular differentiation in pleomorphic adenomas. In conclusion, a large portion of pleomorphic adenomas of the salivary gland origin, but not of palate origin, was shown to overexpress BMP-6 protein.     

Expression of bone matrix proteins, osteonectin and osteopontin, in salivary pleomorphic adenomas

Osteonectin (OSN) is a glycoprotein involved in the early steps of the mineralization of skeletal tissue, while osteopontin (OPN) is a protein involved in normal and pathological calcifications. OSN and OPN are non-collageneous bone matrix proteins expressed by some epithelial tumor cells in exceptional cases. We immunohistochemically investigated the presence and the distribution of OSN and OPN in 43 pleomorphic adenomas to elucidate the production of their molecules by modified myoepithelial cells. In normal salivary glands, OSN was immunolocalized in the striated ducts, while OPN was not expressed. In pleomorphic adenomas, the inner layer of tubulo-glandular structures and modified myoepithelial cells in the myxoid areas showed moderate positivity for OSN (83.7%). OSN was expressed in all of the lacuna cells in the chondroid areas. OPN was strongly expressed in the stroma of the myxoid and hyaline areas of the pleomorphic adenomas (65.1%), but there was no expression of OPN in the chondroid area. All cases of pleomorphic adenomas expressed type IV collagen. These findings suggested that OSN was related to the production of the type IV collagen by modified myoepithelial cells, whereas OPN was involved in the stromal formation of myxoid or hyaline tissues in pleomorphic adenomas. In summary, pleomorphic adenomas expressed the bone matrix proteins OSN and OPN.     

Ultrastructural immunolocalization of a cartilage-specific proteoglycan,aggrecan, in salivary pleomorphic adenomas

A pleomorphic adenoma (PA) is the most common epithelial tumor in the salivary glands, but it frequently shows a mesenchyme-like histology, including the presence of myxoid and chondroid areas. Cartilage-specific matrix proteins are deposited in PA. Aggrecan is a major component of cartilage-specific proteoglycans. The present study examined the ultrastructure of the stromal areas in ten salivary PA specimens and investigated the distribution of aggrecan by immunoelectron microscopy. Aggrecan was deposited in the myxoid and chondroid stroma of PA. Ultrastructural observations revealed many proteoglycan cores and fibrils in the myxoid stroma and some spindle-shaped neoplastic myoepithelial cells with vacuoles and actin filaments in the myxoid areas. By immunoelectron microscopy, positivity for aggrecan was observed in the vacuoles of neoplastic myoepithelial cells, which coexisted with the viscous materials, and it was also frequently seen in electron-dense crystals in the myxoid stroma. These findings suggest that neoplastic myoepithelial cells produce aggrecan and release it from vacuoles, and aggrecan is then deposited in the myxoid stroma. Aggrecan deposition is therefore considered to play an important role in the formation of the mesenchyme-like stroma, especially the myxoid stroma.     

Expression and amplification of neu oncogene in pleomorphic adenomas of salivary gland.

Amplification of the neu oncogene and overexpression of its product was found to be a potential marker for aggressive biological behavior in breast cancer. However, the expression of the neu oncoprotein in normal breast ducts and myoepithelial cells has also been demonstrated. Hence, we examined normal salivary gland tissue and 15 cases of pleomorphic adenoma for the expression of the neu oncoprotein by immunohistochemistry using two polyclonal antibodies and 12 cases for the amplification of the neu oncogene using slot blot hybridization. Immunohistochemistry in the normal salivary gland revealed positive staining of all ductal cells. In the pleomorphic adenomas all cellular elements stained to a variable degree. The positive staining was seen in the ductal cells, in the solid sheets, and in chondroid, myxoid, and metaplastic foci. The normal salivary gland and 11 of 12 cases of pleomorphic adenoma showed no increase in copy number of the neu oncogene, whereas one case showed threefold amplification. These results indicate that the neu oncoprotein is expressed but the neu copy number is not increased in normal salivary gland epithelium and in most pleomorphic adenomas. The threefold amplification of the gene in one case may indicate an aggressive biological behavior.     

Immunohistochemical demonstration of S-100 protein in salivary gland neoplasms

A peroxidase-antiperoxidase technique for S-100 protein has been applied to 68 salivary glands. These included 17 pleomorphic adenomas, seven adenoid cystic carcinomas, 23 adenolymphomas and a number of other neoplasms. In addition, five specimens of myoepithelial sialadenitis ('benign lymphoepithelial lesion') and five normal parotid glands were included. Consistent results were obtained, myoepithelial cells and cells in myxoid and chondroid areas in pleomorphic adenomas staining intensely. In adenoid cystic carcinoma, on the other hand, there was no staining. The adenolymphomas possessed intensely S-100 protein-positive cells in the interfollicular lymphoid areas; these were probably interdigitating reticulum cells. In addition, branching structures, probably corresponding to Langerhans' cells, were observed in the epithelium of adenolymphomas.     

An immunohistochemical study of bone morphogenetic protein in pleomorphic adenoma of the salivary gland

Bone morphogenetic protein (BMP) is a potent induction factor for new bone formation including heterotopic chondro-ossification in soft tissues. The immunohistochemical reaction for BMP was studied in 23 cases of pleomorphic adenoma of salivary gland by using a monoclonal antibody produced by hybridoma technique. Positive BMP immunoreactivity was seen in 87% of tumours. Immunohistochemical expression of BMP was observed in modified myoepithelial cells (88% cases), luminal tumour cells of tubulo-ductal structures (78% cases) and chondroid cells in hyaline tissue (22% cases). The authors concluded that the simultaneous presence of glycosaminoglycans as matrix substance and S-100 protein for calcium signalling are associated with BMP-mediated cellular activity of modified myoepithelial cells in the formation of chondroid structures in pleomorphic adenomas of the salivary glands.     

Pleomorphic adenoma, II: Ultrastructural organization of "stromal" regions

Findings from an ultrastructural study of 24 major and minor salivary gland pleomorphic adenomas suggest that the principal cell type in the myxoid and chondromyxoid regions of these tumors is a structurally modified myoepithelial cell. This interpretation is based on findings in the transitional zone between myxoid regions and compact cellular areas that have a ductal-acinar organization, that is, are composed of luminal epithelial and modified myoepithelial cells. Survey-type low-power electron micrographs allowed appreciation of the original orientation of the major proliferating component of these tumors to the perimeter of ductal-acinar units. The low-power electron micrographs also revealed residual features of this organization, the early development and subsequent sequential alteration of matrix compartments as tumor cells became increasingly separated by extracellular products, and a variety of myoepithelial cell modifications, such as squamous and chondroid metaplasia, resulting from neoplastic induction. According to the authors' interpretation, modified myoepithelial cells in myxoid and chondromyxoid regions form a continuum with similar tumor cells in transitional and solid areas, forming what can be visualized as markedly expanded and merging ductal-acinar units that tend to converge with similarly altered adjacent neoplastic ductal-acinar units. Thus, a multiplicity of processes are involved in the formation of the complex and varied histologic patterns that characterize pleomorphic adenomas.     

Muscle-specific protein expression in normal salivary glands and pleomorphic adenomas: an immunocytochemical study with biochemical confirmation.

Normal salivary gland myoepithelia are contractile cells with hybrid epithelial/myogenic ultrastructural features. It is known that these cells co-express the intermediate filaments cytokeratin, vimentin, and occasionally GFAP. This complex cytoskeletal immunophenotype is also reflected in multiple morphologic cell types of pleomorphic adenoma. At present, the myofilament complement of normal and neoplastic myoepithelium is not well defined. We have evaluated the expression of desmin and smooth and sarcomeric muscle actins in 11 normal salivary glands (six snap-frozen and five methacarn fixed) and 26 pleomorphic adenomas (11 snap-frozen and 15 methacarn fixed) by ABC-immunoperoxidase method. Two of 11 frozen pleomorphic adenomas contained the muscle-specific intermediate filament desmin, which is not found in the normal glands. This novel finding was confirmed by gel electrophoresis and immunoblot. Using specific antibodies, normal gland myoepithelial cells consistently contained muscle actin isoforms of the smooth muscle type but not sarcomeric muscle actins. Muscle actin expression by the neoplastic cells of pleomorphic adenoma was found in 13 of 26 tumors (six of 11 frozen tumors (desmin negative) and seven of 15 methacarn fixed tumors). In comparison to the normal myoepithelial cell, the transformed myoepithelial-like cells of pleomorphic adenoma are not always characterized by a muscle actin cytoskeleton. Expression of desmin intermediate filaments in pleomorphic adenomas appears to be a rare event that is independent of a muscle actin cytoskeleton.     

An immunohistochemical study of bizarre neoplastic cells in pleomorphic adenoma: its cytological nature and proliferative activity

The cytological nature and proliferative activity of bizarre neoplastic cells, widely scattered in pleomorphic adenomas of salivary gland origin were studied. Pleomorphic adenomas containing numerous bizarre neoplastic cells were found in four cases, and were equal to 2.9% of all pleomorphic adenomas examined. All four cases presented as well-circumscribed, firm masses measuring less than 1.5 cm in size, located in the palate, and were of 7 months to 4 years duration. Histopathologically, these pleomorphic adenomas were cell rich type, and were well demarcated from surrounding tissues, although their fibrous capsules were partially defective. In addition to characteristic histopathological findings of pleomorphic adenoma, numerous neoplastic cells with bizarre appearance were scattered throughout the lesion, excepting for tubuloductal structures. These bizarre neoplastic cells had irregular-shaped and large nuclei with or without hyperchromatism, although their nucleoli were small and mitotic figures were few. Furthermore, there were many multinucleated giant cells, some of which showed multilobulated nuclei. Neither necrosis nor infarct was seen in the tumors. Immunohistochemically, bizarre neoplastic cells scattered in solid-proliferating areas and myxoid areas were neoplastic myoepithelial cells in nature. There was no statistical significance of MIB-1 labeling indices between pleomorphic adenomas with bizarre neoplastic cells and usual pleomorphic adenomas. The p53 labeling indices were quite low. Although the benign nature of pleomorphic adenomas with numerous bizarre neoplastic cells and hypercellularity, distinguishing such pleomorphic adenomas from various stages of malignant transformation in pleomorphic adenomas and other carcinomas should be made by histological section of submitted biopsy specimen or aspirated content for cytological diagnosis. The present paper suggests that the term 'bizarre cell pleomorphic adenoma' is an appropriate name for this neoplasm, in that it is distinguished from the usual benign pleomorphic adenoma which is easily diagnosed by routinely prepared histological or cytological stainings.     

Immunohistochemical localization of vitamin B12 R-binder in salivary gland tumors. Implications for cell differentiation

Vitamin B12 R-binder, a specific binding protein for vitamin B12, was studied immunohistochemically in normal and 106 neoplastic salivary gland tissues with a monoclonal antibody against vitamin B12 R-binder (R-binder). In normal salivary glands, R-binder localization was restricted to the ductal systems and to mucous acinar cells; serous acinar cells, myoepithelial cells and stromal connective tissues were consistently negative. Among salivary gland tumors, R-binder was present in 87% of pleomorphic adenomas, 100% of monomorphic adenomas, and 40% of adenoid cystic carcinomas; positivity was observed only on luminal surfaces of small ductular elements, indicating that the components closely related to ductal differentiation were rather small in population. R-binder could be detected both in lacunar and non-lacunar cells within chondroid areas of pleomorphic adenomas, suggesting the possibility that chondroid regions arise from metaplastic changes in ductal epithelial cells. In mucoepidermoid tumors, mucous cells and focal squamous cells exhibited cytoplasmic staining. The staining pattern for R-binder in epithelial components of adenolymphomas showed close similarities to those found in normal large excretory ducts. Two acinic cell tumors and one case each of myoepithelioma and malignant myoepithelioma exhibited negative reactivity for R-binder, showing that these neoplasms are solely composed of tumor cells without the characteristics of ductular differentiation. The immunohistochemical examination of salivary gland tumors, employing a monoclonal anti-R-binder antibody, may have some implications for cellular heterogeneity and differentiation in various tumors.     

PLAG1 gene alterations in salivary gland pleomorphic adenoma and carcinoma ex-pleomorphic adenoma: a combined study using chromosome banding, in situ hybridization and immunocytochemistry.

Pleomorphic adenoma is the most common benign tumor of the salivary glands. It has marked histological diversity with epithelial, myoepithelial and mesenchymal-type cells arranged in a variety of architectural and differentiation patterns. Pleomorphic adenoma gene 1 (PLAG1), shown to be consistently rearranged in pleomorphic adenomas, is activated by chromosomal translocations involving 8q12, the chromosome region that is most frequently affected in these tumors. In this study, we evaluated PLAG1 involvement in salivary gland tumorigenesis by determining the frequency of its alterations in a selected group of 20 salivary gland tumors: 16 pleomorphic adenomas and four carcinomas ex-pleomorphic adenoma, having in common the presence of karyotypic chromosome 8 deviations, either structural, with 8q12 rearrangements, or numerical, with gain of chromosome 8. PLAG1 status was analyzed using in situ hybridization techniques, on metaphase cells, by fluorescence detection and/or interphase cells in paraffin sections, by chromogenic detection. Except for one pleomorphic adenoma case (5%) that lacked PLAG1 involvement, 17 tumors (85%), (14 pleomorphic adenomas and three carcinomas ex-pleomorphic adenoma) showed intragenic rearrangements of PLAG1 and the remaining two cases (10%), (one pleomorphic adenoma and one carcinoma ex-pleomorphic adenoma), had chromosome trisomy 8 only. To further investigate the role of PLAG1 on pleomorphic adenomas tumorigenesis, as well as the putative morphogenesis mechanism, we attempted to identify the cell types (epithelial vs myoepithelial) carrying 8q12/PLAG1 abnormalities by a combined phenotypic/genotypic analysis in four cases (three pleomorphic adenoma and one carcinoma ex-pleomorphic adenoma) characterized by 8q12 translocations and PLAG1 rearrangement. In these cases, both cells populations carried PLAG1 rearrangements. This finding further supports the pluripotent single-cell theory, which postulates that the tumor-initiated, modified myoepithelial cell, evolves into the varied somatic cell phenotypes present in pleomorphic adenoma, and reinforces the role of PLAG1 on the tumorigenesis of benign and malignant pleomorphic adenoma.     

Phosphatase enzymes. Cytochemical study of pleomorphic adenoma and normal human salivary glands.

Human parotid glands, submandibular glands, and pleomorphic adenomas were examined by electron microscopic histochemistry. All epithelial cells of the normal salivary glands showed plasma membrane adenosine triphosphatase (ATPase) and inosine diphosphatase (IDPase) activity. However, myoepithelial cells reacted most intensely. Pleomorphic adenomas showed epithelial cells within solid and ductal portions of the tumors that were variably reactive for both ATPase and IDPase. Histochemical examination of the epithelial cells in the myxoid portions of the tumors did not provide conclusive evidence as to the nature of their progenitor cells. Surface-associated phosphatases (alkaline phosphatase, ATPase, and IDPase) cannot be reliably used as histochemical markers of salivary gland myoepithelial cells. Therefore, morphological and phosphatase histochemical studies that intend to examine the role of myoepithelial cells in salivary gland neoplasms must be interpreted with care.     

Fine‐needle aspiration (FNA) and pleural fluid cytology diagnosis of benign metastasizing pleomorphic adenoma of the parotid gland in the lung: A case report and review of literature

Lesions that contain abundant benign myoepithelial cells, including pleomorphic adenomas of salivary gland origin, may present a diagnostic challenge in fine‐needle aspiration (FNA) specimens. Benign metastasizing pleomorphic adenoma is a rare neoplasm, in which the benign appearing pleomorphic adenoma, without any histological evidence of malignancy, metastasizes to distant sites including lung. In the absence of clinical history of a pre‐existing myoepithelial neoplasm, the presence of myoepithelial cells in the lung or any other organs besides salivary glands may create diagnostic difficulty. Here we present the cytologic findings of such a metastatic tumor found in the lung FNA and pleural fluid specimens from a 64‐year‐old woman, with a history of local recurrent salivary gland pleomorphic adenomas, who presented with multiple bilateral pulmonary nodules and pleural effusion. The diagnosis of benign metastasizing pleomorphic adenoma was made based on clinical information and cytomorphology, and confirmed by immunocytochemistry. Diagn. Cytopathol. 2009. © 2009 Wiley‐Liss, Inc.     

Comparative histogenesis and morphogenesis of mucoepidermoid carcinoma and pleomorphic adenoma

Summary Current classifications of salivary gland tumors separate mucoepidermoid carcinoma from other neoplasms on the basis of a number of histological features, in particular the lack of participation of neoplastic myoepithelial cells. However, ultrastructural examination of low- and intermediate-grade mucoepidermoid carcinomas and pleomorphic adenomas reveals many common organizational and cellular features. Of prime importance is the relationship of intermediate cells to the luminal cells in mucoepidermoid carcinomas, which is remarkably similar to that seen between modified myoepithelial cells and luminal cells in pleomorphic adenomas. The results suggest that intermediate cells of mucoepidermoid carcinoma are the counterpart of the modified myoepithelial cells of pleomorphic adenoma. The generally accepted hypothesis that the former tumor develops from an excretory duct reserve cell, while the latter originates from an intercalated duct stem cell does not seem to be valid; pleomorphic adenoma and mucoepidermoid carcinoma appear to be closely related morphologically.     

Immunohistochemical distribution of human epidermal growth factor in salivary gland tumours

Summary Immunohistochemical identification of human epidermal growth factor (hEGF) was carried out in a total of 152 cases of salivary gland tumours, consisting 107 pleomorphic adenomas and their variants, 13 adenolymphomas and 32 adenoid cystic carcinomas. A high percentage of pleomorphic adenomas revealed markedly positive hEGF staining of the luminal surface cells of tubuloductal structures and of modified or neoplastic myoepithelial cells. Clear cells of the tumour showed various reactivities from very slight to strong. Eosinophilic epithelial cells of adenolymphoma gave a positive reaction for hEGF in all the cases, whereas most adenoid cystic adenoma lacked hEGF staining; however some cases showed positive staining of the tumour cells. The immunohistochemical detection of hEGF in most salivary gland tumours suggests this factor to be a possible new marker of salivary glands tumours, and to have a biological role in tumour proliferation.     

Reconstruction of pleomorphic adenoma of the salivary glands in three-dimensional collagen gel matrix culture

 The morphogenesis of salivary gland pleomorphic adenoma was examined in vitro using three-dimensional (3-D) collagen gel culture. Pleomorphic adenoma cells were isolated from three parotid gland tumours and cultured as monolayers, after which they were subcultured in floating-collagen gel sandwiches. Cells cultured in both conditions were immunohistochemically characterized and compared using antibodies against various proteins representative of each histological component of salivary glands. Monolayers had myoepithelial characteristics, being positive for vimentin and α-smooth muscle actin. In collagen gels, however, the cells assembled in epithelial nests, showing an architecture similar to that of pleomorphic adenoma. The nests were composed of duct-lining epithelial cells that were positive for epithelial markers, surrounded by myoepithelial cells. Collagen gel culture induces multi-directional differentiation of adenoma cells, suggesting that pleomorphic adenomas originate from stem or reserve cells. Received: 26 March 1998 / Accepted: 1 September 1998