Myofilament localization and immunoelectron microscopic detection of muscle-specific actin in neoplastic myoepithelial cells in pleomorphic adenomas and myoepitheliomas

Oral cavity salivary gland pleomorphic adenoma: a histomorphological case series

BACKGROUND

Pleomorphic adenoma (PA), the most common benign salivary gland epithelial lesion, has a biphasic epithelial-mesenchymal pattern and great histopathological diversity.

METHODS

This study's objective was to conduct a retrospective clinicopathological analysis, focusing on the histopathology characteristics of salivary gland PA.

RESULTS

There were ten cases of pleomorphic adenoma. The mean age was 33.5 years and no gender predilection was observed. All the patients presented with an asymptomatic mass and the duration of presentation was 31.2 ± 19.4 months. The cellular subtype (50 %) of PA was the most common. Capsular infiltration and incomplete capsules occurred in 20 % of cases. All the cases had round (100 %) and myxoid stroma. The cellular subtype was more common in the major salivary glands; showed capsular abnormalities (incomplete capsule, absent capsule, and tumor infiltration); and had more plasmacytoid, angular, spindled non-luminal cells as well as inflammation and cystic degeneration. The classic subtype had more clear and oncocytic cells along with sebaceous and squamous differentiation. The stroma-rich subtype had the shortest duration of complaints (three months) and showed giant cell reaction.

CONCLUSIONS

These findings confirm previous studies on the clinicopathological features of pleomorphic adenomas and highlight important morphologic characteristics like capsular invasion and squamous metaplasia, which can otherwise indicate malignancy.

Secretory myoepithelial carcinoma: a histologic and molecular survey and a proposed nomenclature for mucin producing signet ring tumors

Signet ring cell (mucin producing) adenocarcinoma is a rare low grade salivary gland malignancy. While currently designated as an adenocarcinoma, myoepithelial differentiation has been implied in previously reported cases. We herein perform a survey of our cases of signet ring cell adenocarcinoma and review the literature in order to refine categorization of this rare tumor. Five cases were retrieved. One was reclassified as a mammary analogue secretory carcinoma, leaving four that fulfilled the criteria for signet ring cell adenocarcinoma: the presence of prominent signet ring or vacuolated cells arranged in islands, interconnecting strands, cords or sheets in a myxoid or hyaline stroma, or pools of mucin. An extensive panel of histochemical and immunohistochemical stains and fluorescence in situ hybridization (FISH) (modeled after common phenotypes and molecular alterations seen in signet ring and myoepithelial tumors at other sites) was performed. The male-to-female ratio was 3:1. The mean age was 56 years (range 18-81). Sites involved included buccal mucosa (2), soft palate (1) and deep parotid (1). Perineural and angiolymphatic invasion were present in three and two cases respectively. One patient was lost to follow up and the remainder were alive and without disease at time of last follow up (mean 38 months). All cases showed mucicarmine positive vacuolated/signet ring cells embedded in a myxoid stroma. Three cases showed at least focal p63 staining and two cases showed positivity for calponin. Membranous E-cadherin was retained in all cases. FISH was negative for ETV6, EWSR1, and ALK1 rearrangements in all four cases. Based on the current series and the previously reported cases, it is evident that signet ring adenocarcinomas have a dual secretory and myoepithelial phenotype and thus as a whole more appropriately designated as 'secretory myoepithelial carcinoma.' They behave in a fairly indolent fashion and do not share the major molecular alterations seen in other signet ring and myoepithelial tumor types.

Adhesion and protease activity in cell lines from human salivary gland tumors are regulated by the laminin-derived peptide AG73, syndecan-1 and beta1 integrin

We studied the induction of protease activity by the laminin alpha1-derived peptide AG73 in cells from adenoid cystic carcinoma (CAC2) and myoepithelioma (M1), respectively a malignant and a benign salivary gland tumors. Laminin alpha1 chain and MMP9 were immunolocalized in adenoid cystic carcinoma and myoepithelioma in vivo and in vitro. Cells grown inside AG73-enriched laminin-111 exhibited large spaces in the extracellular matrix, suggestive of remodeling. The broad spectrum MMP inhibitor GM6001 decreased spaces induced by AG73 in CAC2 and M1 cells. This result strongly suggests that AG73-mediated matrix remodeling involves matrix metalloproteinases. CAC2 and M1 cells cultured on AG73 showed a dose-dependent increase of MMP9 secretion, as detected by zymography. Furthermore, siRNA silencing of MMP9 decreased remodeling in 3D cultures. We searched for AG73 receptors regulating MMP9 activity in our cell lines. CAC2 and M1 cells grown on AG73 exhibited colocalization of syndecan-1 and beta1 integrin. siRNA knockdown of syndecan-1 expression in these cells resulted in decreased adhesion to AG73 and reduced protease and remodeling activity. We investigated syndecan-1 co-receptors in both cell lines. Silencing beta1 integrin inhibited adhesion to AG73, matrix remodeling and protease activity. Double-knockdown experiments were carried out to further explore syndecan-1 and beta1 integrin cooperation. CAC2 cells transfected with both syndecan-1 and beta1 integrin siRNA oligos showed significant decrease in adhesion to AG73. Simultaneous silencing of receptors also induced a decrease in protease activity. Our results suggest that syndecan-1 and beta1 integrin signaling downstream of AG73 regulate adhesion and MMP production by CAC2 and M1 cells.

Plasmacytoid myoepithelioma of the palate in a child

BACKGROUND

Myoepithelioma is a rare benign salivary gland tumour, localized most frequently in the parotid and in minor intraoral salivary glands. There have been only four cases of myoepithelioma in children and adolescents reported in the English-language literature, all of them involving the plasmacytoid variant.

CASE REPORT

A 13-year-old boy, complained of a painless nodule of the palate. Incisional biopsy was performed and revealed large plasmacytoid cells with a round and eccentric nuclei. The diagnosis was consistent with myoepithelioma, plasmocytoid variant. Tumour cells were positive for cytokeratins, vimentin and S-100 protein. Surgical resection was performed and no evidences of tumour recurrence were observed after 6 years of the treatment.

CONCLUSION

Myoepithelioma is a very rare tumour in children and apparently presents a good prognosis, similar to occur in adult patients.

Mixed tumors of the vagina: an immunohistochemical study of 13 cases with emphasis on the cell of origin and potential aid in differential diagnosis

Mixed tumors of the vagina (MTsV) are rare benign neoplasms characterized by an admixture of well-differentiated epithelial cells and stromal-type cells in various proportions. In contrast to mixed tumors in other anatomic sites, the histogenesis of the vaginal tumors is unclear. We studied the immunohistochemical profile of 13 examples to explore their histogenesis and determine whether their immunohistochemical profile might be useful in the differential diagnosis. The panel of antibodies used and the number of cases studied were: AE1/3 (12), cytokeratin 7 (CK7) (13), cytokeratin 20 (CK20) (13), epithelial membrane antigen (EMA) (13), muscle actin (MA) (12), desmin (11), h-Caldesmon (13), CD10 (13), CD34 (11), CD99 (8), and S-100 (7). Eight out of 12 tumors were positive for AE1/3, 7/13 for CK7, 2/13 for CK20, and 6/13 for EMA. MA was positive in 11/12 mixed tumors, desmin in 10/11 tumors and h-Caldesmon in 5/13. All tumors were extensively positive for CD10; CD34 was positive in 7/11; and none out of eight tumors showed membranous CD99 staining. Focal S-100 immunoreactivity was seen in 1/7 tumors. These results show that MTsV coexpress epithelial and mesenchymal markers. The expression of muscle actin (usually extensive), and focal desmin and h-Caldesmon positivity suggests the presence of a smooth muscle or myoepithelial component; however, the S-100 negativity and diffuse CD10 expression argue against it. Positivity for muscle markers does not help distinguish MTsV from smooth muscle or skeletal muscle tumors. The frequent expression of CD10 negates its use in the differential diagnosis with endometrial stromal tumors, and the CD10 and CD34 expression suggests that mixed tumors may arise from a primitive pluripotential cell. MTsV are positive for h-Caldesmon and CD10, two markers that have been used in gynecologic pathology primarily to aid in establishing the smooth muscle or endometrial stromal phenotype of a neoplasm.

The effect of laminin and its peptide SIKVAV on a human salivary gland myoepithelioma cell line

We have demonstrated that the basement membrane regulates the myoepithelioma. We are now studying the effect of laminin, a basement membrane protein, in the morphology of a cell line (M1) derived from human salivary gland plasmacytoid myoepithelioma. These cells were grown inside a three-dimensional preparation of laminin-1. Phenotype differences were assessed by light and transmission electron microscopy. In addition, we analysed the effect of a molecular domain of laminin-1, the peptide SIKVAV, on M1 cells. This peptide was chosen because it is effective in cell proliferation and differentiation. M1 cells grown inside laminin-1 were mostly plasmacytoid-like, while cells treated by SIKVAV showed light and electron microscopic features of typical plasmacytoid cells. This peptide also modulated smooth-muscle actin expression in M1 cells. We demonstrated that laminin-1 and its derived peptide SIKVAV morphoregulates myoepithelioma cells in culture.

Special techniques in diagnostic electron microscopy

The power of electron microscopy as a diagnostic tool can be amplified considerably by the application of ancillary preparative and analytic methods. Subcellular chemistry and structure can be examined by various forms of microprobe analysis and by special staining methods, including cytochemical, immunocytochemical, and negative staining. Qualitative ultrastructural examination can be augmented by morphometric analysis. Correlative microscopic survey methods can be used as a means of targeting ultrastructural investigations. This article provides an overview of the use of these special techniques in the diagnosis and classification of tumors and other selected pathologic processes.

Differentiating myoepithelial and acinar cells in rat neonatal parotid gland and histogenetic concepts for salivary gland tumors

Histogenetic concepts for salivary gland tumors are predicated on the presence of reserve or undifferentiated cells in normal glands, presumably the source for cell renewal and induction of tumors. Developing rat parotid gland, which remains fetal-like at birth, provides the opportunity to study differentiation and observe whether cytologically undifferentiated cells do or do not have functional indicators of specific differentiation pathways. Immunohistochemistry and immuno-electron microscopy, when applied to parotid gland at birth, at 12 days of age and in the adult gland, indicate that commitment to myoepithelial cell differentiation occurs prior to development of structural changes characteristic of these cells. Conversely, secretory granules are evident in differentiating acinar cells prior to synthesis of amylase. The results suggest that an appearance of undifferentiation does not confer reserve cell status either in the normal salivary gland or their tumors.

Myoepithelioma: definitions and diagnostic criteria

Due to their infrequency and multiplicity of histopathology, myoepitheliomas present difficulties in diagnosis and classification. Cellular varieties can be misdiagnosed as malignancies. Improvements in and clarification of diagnostic criteria are, therefore, required. A key to determining diagnostic criteria for myoepitheliomas is to study cellular morphology, cytoplasmic filament expression, and ultrastructural features of the nonluminal, i.e., neoplastic myoepithelial/basal, tumor cells of pleomorphic adenomas, and apply this information to defining myoepitheliomas. Cytologic and growth patterns of nonluminal cells in pleomorphic adenomas, including plasma-cytoid cells, are reflected in myoepitheliomas. Results also indicate that muscle-specific actin and myofilaments are expressed only in a proportion of cases, and generally in not more than 60-70% of nonluminal cells in pleomorphic adenoma; this also applies to benign and malignant myoepitheliomas. The absence of these markers does not exclude a diagnosis of myoepithelioma. Vimentin and glial acidic fibrillary protein, however, are strongly and diffusely expressed in the majority of pleomorphic adenomas and myoepitheliomas and are more reliable markers for these tumors than muscle-specific actin. Like so many other salivary gland tumors, myoepitheliomas present an equally complex histomorphology and variable expression of antigenic markers, only some of which are associated with myoepithelial and basal cells of the acini and ducts of the normal salivary gland.