Basal cell adenoma with myoepithelial cell-derived "stroma": a new major salivary gland tumor entity

Basal Cell Adenoma of the Minor Salivary Glands in the Buccal Mucosa: A Rare Entity Arising in an Unusual Location

One of the rare tumors of the salivary gland is known as basal cell adenoma (BCA). Only a small percentage of salivary gland tumors affect the minor salivary gland of the oral cavity while the majority are found in the parotid gland. We present a rare case of BCA involving the left buccal mucosa of a 45-year-old female. Magnetic resonance imaging (MRI) showed well defined solid mass measuring 1.9 x 1.5 cm in the left buccal space inseparable from the buccinator muscle. The T2-weighted image demonstrates a hyperintense signal post-contrast. Ultrasound-guided fine needle aspiration cytology revealed cellular basaloid neoplasm of uncertain malignant potential. Thereafter excision of the mass was performed through a transoral approach under general anesthesia. Histopathology of the mass showed encapsulated basal cell neoplasm in favor of BCA. The patient was doing well after the surgery and has intact facial nerve and adjacent nerves such as the auriculotemporal nerve and great auricular nerve with no complications then she kept on routine clinic follow-ups, and the surgical site recovered successfully. Therefore, we conclude that MRI and biopsy provide useful information to differentiate between benign adenoma and malignant adenocarcinoma. BCA should be considered in a differential diagnosis of an isolated neck mass. Surgical excision demonstrates an excellent prognosis.

Epithelial-Myoepithelial Carcinoma

Epithelial-myoepithelial carcinoma is an uncommon low-grade salivary gland carcinoma. It is classically characterized by biphasic tubular structures composed of inner eosinophilic ductal cells and outer clear myoepithelial cells. In addition, epithelial-myoepithelial carcinoma sometimes shows various histologic features, including a cribriform pattern, basaloid appearance, and sebaceous differentiation. Because clear myoepithelial cells are also noted in other benign and malignant salivary gland tumors, the histologic variety and similarity with other tumor entities make the diagnosis of epithelial-myoepithelial carcinoma challenging. A recent analysis revealed that HRAS hotspot point mutations are specifically identified in epithelial-myoepithelial carcinoma and the assessment of given genes facilitate the correct diagnosis.

Immunohistochemical evaluation of salivary gland tumors differentiation and proliferation by using calponin and telomerase

Background

Salivary gland tumors are a heterogeneous group of lesions with diverse histological features. Hence they are considered as a diagnostic challenge for the pathologist. Myoepithelial cells are considered as a key in the morphogenetic process, with diverse differentiation in various salivary gland tumors. Calponin is an actin filament- associated protein that represents a sensitive marker of myoepithelial cells. Telomerase is a ribonucleoprotein that adds telomere repeats at the end of chromosomes in order to prevent replicative senescence. It has a key role in cellular immortality and tumorgenesis of various tumors. This study evaluates the immunohistochemical expression of calponin and telomerase in various salivary gland tumors.

Methods

This retrospective study involved 30 formalin fixed paraffin embedded blocks of salivary gland tumors. The immunohistochemical staining and evaluation of subcellular localization, pattern, intensity, and distribution for calponin and immune scoring for telomerase were done. The statistical analyses of data were conducted by Chi-square and ANOVA-test, a P-value of <0.05 was considered significant.

Results

Calponin showed expression at the periphery of acini and intercalated ducts in the normal salivary gland. It revealed cytoplasmic expression in 83.3% of benign tumors. The pleomorphic adenoma showed a diffuse pattern of staining (85.7%), strong intensity (64.3%), and mixed distributions (57.1%). The diffuse pattern of calponin was seen in all cases of mucoepidermoid, polymorphous low-grade adenocarcinoma and epithelial-myoepithelial carcinoma (100%). Telomerase revealed negative expression in the normal salivary gland. Pleomorphic adenoma illustrated high telomerase expression in score 2 and score 3 (93.3%). Telomerase immune scoring is significantly related to the benign tumors as P value was 0.03. Both polymorphous low grade and epithelial-myoepithelial carcinoma were detected only in score 3. Finally, the mean level of telomerase activity was slightly higher in malignant tumors than benign ones with non-significant relation as P value was 0.6.

Conclusions

Calponin showed high diffuse staining with altered distribution in salivary gland tumors, which might give an additional role for this marker in the identification of luminal immuno-modified neoplastic cells. Telomerase is considered as a useful marker in identifying proliferation capacity of salivary gland tumors and is remarkably more detected in malignant salivary gland tumors.

Salivary Gland Tumors: Current Concepts and Controversies

This current review focuses on current concepts and controversies for select key salivary gland epithelial neoplasms. Rather than the traditional organization of benign and malignant tumors, this review is structured around select key topics: biphasic tumors, mammary analogue secretory carcinoma, and the controversy surrounding polymorphous low-grade adenocarcinoma and cribriform adenocarcinoma of (minor) salivary gland origin.

A case of Basal cell adenoma of the upper lip

Basal cell adenoma is a rare type of benign salivary gland tumor found most commonly in the parotid gland. We present a rare case of basal cell adenoma arising in the minor salivary gland of the upper lip. The patient was a 59-year-old Japanese man who visited our department in December 2012 with a chief complaint of a mass in the upper lip, which had increased in size over several years. A mobile, elastic, and relatively soft mass without tenderness was palpable in the upper lip region. The mucosa of the upper lip covering the mass was normal. Tumor extirpation was performed under local anesthesia. Histologically, the tumor had a capsule and was composed of islands of relatively uniform, monotonous cells. Immunohistochemically, the inner tumor comprised tubuloductal structures that showed strong staining for CK7, while the outer tumor showed weak staining for CK7. The outer tumor cells also stained positively for CD10 and p63. The MIB-1 (Ki-67) labeling index was extremely low. Basal cell adenoma was diagnosed based on these results. The postoperative course was uneventful 12 months after surgery and there has been no recurrence.

Nestin is a wide-spectrum abluminal cell marker of salivary gland tumors

Nestin is an intermediate filament that was first identified in neural progenitor cells. It is expressed in various cell types in the nervous system as well as in other systems. In the present study, we investigated nestin expression in non-neoplastic salivary gland tissue and in salivary gland tumors. In non-neoplastic salivary glands, nestin expression was observed in only a few abluminal cells. In contrast, diffuse nestin staining was observed in the abluminal cells of pleomorphic adenoma (11 of 11 cases), basal cell adenoma (7 of 7 cases), and epithelial-myoepithelial carcinoma (2 of 2 cases). The stromal cells in basal cell adenoma also expressed nestin. In adenoid cystic carcinoma (6 of 7 cases) and polymorphous low-grade adenocarcinoma (3 of 3 cases), nestin positive cells were observed focally. Nestin was not detected in Warthin tumor (6 cases), classical acinic cell carcinoma (2 cases), mucoepidermoid carcinoma (5 cases), or salivary duct carcinoma (4 cases). Because the nestin expression pattern in each histological salivary gland tumor type is unique, nestin could be a very useful abluminal cell marker for the diagnosis of salivary gland tumors.

Rare Malignant and Benign Salivary Gland Epithelial Tumors

Although at least 24 distinct histologic salivary gland carcinomas exist, many of them are rare, comprising only 1% to 2% of all salivary gland tumors. These include epithelial-myoepithelial carcinoma, (hyalinizing) clear cell carcinoma, basal cell adenocarcinoma, cystadenocarcinoma, low-grade salivary duct carcinoma (low-grade cribriform cystadenocarcinoma), oncocytic carcinoma, and adenocarcinoma not otherwise specified. Few tumors (clear cell carcinoma and basal cell adenocarcinoma) have unique molecular correlates. Benign tumors, although histologically less diverse, are far more common, with pleomorphic adenoma and Warthin tumor the most common salivary gland tumors. Many benign tumors have malignant counterparts for which histologic distinction can pose diagnostic challenge.

Unusual neck mass in an adolescent: benign basal cell adenoma of the minor salivary glands of the piriform sinus

With an incidence of less than 3%, salivary gland tumors are rare in the head and neck. The percentage of basal cell adenomas within the group of salivary gland tumors is even less (0.2-2%). Salivary gland tumors occur very rarely in adolescents. The basal cell adenoma commonly affects older persons and occurs most frequently in the major salivary glands. We present the unusual case of a benign basal cell adenoma of the minor salivary glands of the piriform sinus in a 14 year old male patient. Unusual are the age of the patient, the histological type, size and localisation of the tumor.

Salivary gland-like tumors of the sellar region

Herein we present a group of rare tumors of the sella region that have not been previously recognized. Although clinically and radiographically the tumors resemble nonfunctioning pituitary adenomas, their histologic, immunohistochemical, and ultrastructural features differ and indicate a salivary gland origin. The lesions cover a morphologic spectrum that includes cellular pleomorphic adenoma, monomorphic adenoma, oncocytoma, and low-grade adenocarcinoma of the salivary gland. All tumors except the oncocytoma were immunoreactive for cytokeratin and were negative for pituitary hormones and synaptophysin. Ultrastructural characteristics in the cases examined include hypodense stromal material, basal lamina, and tonofilament bundles. The single oncocytoma was packed with mitochondria and lacked membrane-bound secretory granules. DNA ploidy based on image analysis and MIB-1 labeling indices showed diversity within this group of tumors, with labeling indices ranging from 0.06% to 15%. The presumed origin of these rare neoplasms is from salivary gland rests related to the normal pituitary gland. Despite their varied morphology, such tumors are easily confused with pituitary adenoma. Although rare, tumors of salivary gland origin should be considered in the differential diagnosis of unusual adenohypophyseal tumors.

Immunohistochemistry of basal cell adenoma of the major salivary glands

An immunohistochemical study of basal cell adenoma of the major salivary glands was performed. All basal cell adenomas showed similar staining patterns. Carcinoembryonic antigen was expressed in the apical portions of luminal cells, in the luminal secretions, and in the duct-lining cells. Epithelial membrane antigen showed a similar pattern of expression but was less frequently present in duct-lining cells. Keratin expression was found in all epithelial cells but not in stromal cells. S-100 protein was strongly expressed in stromal cells, with focal positivity of cells in epithelial nests. Vimentin expression was noted in stromal cells and the outer layer of epithelial nests. Staining for muscle-specific actin was negative in both stromal cells and epithelial nests. Thus, there appears to be evidence of myoepithelial cell participation in the histogenesis of basal cell adenomas, and at least some basal cell adenomas appear to be closely related to pleomorphic adenomas.

Pathology of the salivary glands: the contribution of electron microscopy

Electron microscopy has a limited role in the diagnosis of primary salivary gland tumors, although it can be helpful in metastatic lesions of possible salivary gland origin. The diversity of subtypes in salivary gland tumors, as well as the range of histomorphology within any one subtype, is unparalleled in any other human tumor. This and their relative infrequency causes diagnostic problems for pathologists. Ultrastructural techniques have been of major importance in determining the inter-relationship of these tumors for classification purposes, revealing the subtle variations in common cellular differentiation pathways, determining the organization of tumor cells, and displaying the importance of extracellular matrix materials in establishing diagnostic criteria for each of the many subtypes. Electron microscopy has also been valuable in non-neoplastic salivary gland disease and has an increasing role in experimental studies involving tissue from human and animal salivary parenchyma.

The World Health Organization's Histological Classification of Salivary Gland Tumors. A commentary on the second edition

The second edition of the World Health Organization's Histological Classification of Salivary Gland Tumors is more extensive and detailed than the previous edition published 20 years ago. The new edition is based on data regarding newly described tumor entities and the behavior and prognosis of the previously classified tumors. The distinct morphologic features of monomorphic adenomas justify their separation for purposes of identification. Among the carcinomas, various types were distinguished for purposes of recognition, prognosis, and treatment. The term tumor was replaced by carcinoma in the following two entities: acinic cell carcinoma and mucoepidermoid carcinoma. The tumor-like lesions were described in more detail.

Troublesome tumours 2: borderline tumours of salivary glands

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Trabecular and solid-cribriform types of basal cell adenoma. A morphologic study of two cases of an unusual variant of monomorphic adenoma

Monomorphic adenomas are a morphologically complex group of salivary gland tumors. Two unusual examples, one a trabecular and the other a solid form of basal cell adenoma, reveal the development of a cribriform growth pattern focally in the former example and diffusely in the latter. They illustrate the potential for cellular differentiation within this subgroup, organization of synthetic products by the tumor cells, and the histologic criteria useful for the distinction of basal cell adenoma from adenoid cystic carcinoma.

Basaloid monomorphic adenomas

Monomorphic adenomas can be divided into basaloid and nonbasaloid type. With the exception of the canalicular adenoma, the basaloid monomorphic adenomas are preponderantly tumors of the major salivary glands, most often the parotid gland. The dermal analogue monomorphic adenomas, so named because of their histologic similarity to eccrine tumors of the skin, are a unique subset of the basaloid adenomas. They are often multifocal, recur frequently, may undergo malignant change, and can be part of a salivary-cutaneous tumor diathesis.

The cellular composition of basal cell adenoma of the parotid gland: an immunohistochemical analysis

Four cases of basal cell adenoma of the parotid gland were examined immunohistochemically to characterize their cellular composition. In all cases epithelial membrane antigen and keratin were detected in the inner luminal cells; some cells also showed positive staining for secretory functional markers, indicating their differentiation toward secretory epithelium. In tubular and trabecular types the outer cells consistently displayed an intense staining for vimentin and some were also positive for actin, indicating their myoepithelial nature. In the solid type, most tumor cells resembled the ductal cells or basal cells of larger ducts in normal gland with regard to their immunoreactivity. Our results may suggest that the proportion and arrangement of heterogeneous tumor cells are responsible for different histologic patterns of the salivary basal cell adenoma.

WHO International Histological Classification of Tumours. Tentative Histological Classification of Salivary Gland Tumours

The principles of the proposed modified WHO Histological Typing of Salivary Gland Tumours are based on the following: 1) The classification of tumours is oriented to the routine work of the practicing surgical pathologists, those who do not see tumours of the salivary glands very often. The inclusion of rare, but clearly defined tumour entities should be helpful to surgical pathologists consulting with clinical specialists. 2) The different types of carcinomas must be distinguished not only by precise histopathological definitions, but also considering differences in prognosis and treatment. For example, the polymorphous low-grade adenocarcinoma and the epithelial-myoepithelial carcinoma are characterized by a relatively good prognosis in contrast to the salivary duct carcinoma. 3) Special points of discussion are: subclassification and grading of carcinomas (e.g. acinic cell carcinoma, mucoepidermoid carcinoma and adenoid cystic carcinoma), the classification of basal cell tumours (basal cell adenoma, basal cell carcinoma, solid type of adenoid cystic carcinoma), malignant tumours in pleomorphic adenomas and the differential diagnosis between primary tumours and metastases.