|Year : 2003 | Volume
| Issue : 2 | Page : 54-56
Epithelial myoepithelial carcinoma of palate: A case report
PC Munot1, SM Ganvir1, RS Dolas2, VK Hazarey1
1 Department of Oral and Maxillo Facial Pathology and Microbiology, GDCH, Nagpur, India
2 Department of Oral and Maxillo Facial Surgery, GDCH, Nagpur, India
V K Hazarey
Department of OMFPM, GDCH, Nagpur 63
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Clear cell tumours frequently pose a challenge to the pathologist since the classical morphological features of malignancy exemplified by cytological atypia are frequently absent in malignant clear cell variants, thereby excluding reliance on this histopathological hallmark for the establishment of a diagnosis. Epithelial myoepithelial carcinoma is a rare biphasic low-grade salivary gland malignancy with a prominent clear cell component. We report a case of epithelial myoepithelial carcinoma in the palate of 50-year-old male.
Keywords: Epithelial myoepithelial carcinoma, intercalated duct, biphasic, myoepithelial cell.
|How to cite this article:|
Munot P C, Ganvir S M, Dolas R S, Hazarey V K. Epithelial myoepithelial carcinoma of palate: A case report. J Oral Maxillofac Pathol 2003;7:54-6
|How to cite this URL:|
Munot P C, Ganvir S M, Dolas R S, Hazarey V K. Epithelial myoepithelial carcinoma of palate: A case report. J Oral Maxillofac Pathol [serial online] 2003 [cited 2020 Oct 26];7:54-6. Available from: https://www.jomfp.in/text.asp?2003/7/2/54/40940
| Introduction|| |
Neoplasms with preponderant clear cell composition have been called 'clear cell tumours' but such descriptive designation does little justice to different types of cells, which may be involved/convey reasons from light microscopic appearance of cells. One of the most distinct salivary gland neoplasm with a clear cell component is the epithelial myoepithelial carcinoma (EMC) of intercalated duct. It is a rare biphasic type of low-grade salivary gland carcinoma, which constitutes less than 1% of the salivary gland neoplasms  .
Literature describes this neoplasm under several different names, namely tubular solid adenoma, cystic adenoma, adenomyoepithelioma and clear cell adenoma. The term 'epithelial myoepithelial carcinoma of intercalated duct origin' was introduced by Donath et al in 1972 and has been described in detail by Corio et al  .
| Case Report|| |
A 50-year-old male reported to our institution with the chief complaint of an asymptomatic midpalatal swelling present since 7 years. The swelling had been gradually increasing in size. Pain and parasthesia were present since 15 days. An incisional biopsy was performed by a local dentist 3 years earlier; wherein a histologic diagnosis of pleomorphic adenoma was given (microslides were not available)
Clinical examination revealed a single, wellcircumscribed non-tender swelling seen in the midpalatal region extending from the canine to molar region [Figure 1]. The swelling, measuring 5x6cm 2, was soft anteriorly and firm and lobulated posteriorly. The overlying mucosa was intact and of normal colour. A shallow ulcer was seen on the surface of the tumour. There were no significant extraoral findings or cervical lymphadenopathy.
Based on the previous histopathological report, complete surgical excision of the tumour was done. At surgery, the lesion was found to be well circumscribed and there was no invasion of surrounding tissues. Resected tumour included a 5 mm margin of normal soft tissue and bone with underlying periosteum. Postoperative recovery was uneventful. The patient is being regularly followed up, to check for any recurrence or metastases.
Gross examination of the specimen revealed a greyish pink tumour mass, measuring approximately 6x5x5cm 3 and soft to firm in consistency [Figure 2].
Microscopically, the haematoxylin and eosin stained sections showed a partially encapsulated tumour mass. Lesional tissue was composed of groups of clear cells arranged in lobular pattern separated by hyalinized septa. Individual cells were round/oval with centrally placed nucleus and clear cytoplasm. This clear cell component was seen to predominate in many sections [Figure 3]. Apart from the clear cells, many scattered bizarre cells showing nuclear hyperchromatism, pleomorphism, multilobulation and focal mitotic activity were seen. Groups of plasmacytoid cells were also noted.
In other sections, islands of tumour cells typically arranged in the form of ducts were seen [Figure 4]. These ducts were lined by an inner layer of darkly staining cuboidal cells with eosinophilic cytoplasm and central/basal round nucleus. The outer layer consisted of clear cells with welldefined cell borders and a prominent nucleus. Some of the ductal lumina contained eosinophilic material [Figure 5]. Capsular infiltration by tumour cells was also evident [Figure 6]. Based on the above features, a diagnosis of epithelial myoepithelial carcinoma was made.
| Discussion|| |
EMC is more prevalent in older females and has predilection for occurrence in major salivary glands, especially the parotid. Amongst the minor salivary glands, it is more commonly seen in the palate and tongue. EMC has usually been reported as a swelling without neurological symptoms but occasionally occurs with focal tenderness, pain and/or facial paralysis  .
Inspite of the tumour cells exhibiting a high degree of differentiation, the neoplasm was classified as a carcinoma based on a locally infiltrative and destructive growth pattern, frequent rate of local recurrence, and in a minority of cases, potential for early metastases to regional and distant lymphatics. Histologically, the presence of focal areas of necrosis and perineural involvement tends to further support the malignant nature of the tumour  . Many different types of benign and malignant salivary gland neoplasms such as mixed tumours, oncocytoma, mucoepidermoid carcinoma, acinic cell adenocarcinoma and polymorphous low-grade adenocarcinoma may contain foci of clear cells. When these clear cell foci are a minor component, appropriate identification can be accomplished based on predominant histopathologic features. In rare instances, clear cells may be a major component of tumours such as mucoepidermoid carcinoma, acinic cell adenocarcinoma and oncocytoma. Proper classification of such tumours can be made on basis of morphologic growth pattern and foci with histopathologic features 'typical' of these tumours.
Metastatic disease should always be a consideration in the differential diagnosis of clear cell tumours but location of the neoplasm in this case in the palate, where minor salivary gland aggregates are present, favours a preliminary diagnosis of salivary gland origin. The two metastatic tumours most likely to cause diagnostic difficulties are those from the renal and thyroid primary tumours. Renal cell carcinomas have a solid, organoid growth pattern exhibiting infiltration with little cytologic atypia and few mitosis. Cells are usually mucicarmine positive and show intracytoplasmic lipid and glycogen. Thyroid secondaries contain neither glycogen nor lipid but usually contain thyroglobulin.
Clear cell carcinoma may be considered as one extreme end of the histomorphological spectrum of EMC. However, the bisphasic EMC is still differentiated from monophasic clear cell carcinoma, which lacks the cuboidal eosinophilic lumen lining cells.
According to Carillo et al  , and Arora et al  , cytologic appearance of EMC in FNAC is sufficiently characteristic to permit its diagnosis. The combination of two cellular types (basaloid and clear cells) surrounded by acellular hyaline material constitutes essential features necessary to make the cytologic diagnosis.
The clear cells forming the outer layer of the ductal structures seen in EMC are thought to be neoplastic myoepithelial cells as shown by ultrastructural and immunohistochemical studies , [5, .
Various special stains, immunohistochemistry and electron microscopy can be used to confirm diagnosis. With special stains, the outer epithelial cells are PAS positive and susceptible to diastase digestion; the hyaline basement membrane is positive with PAS and PA methanamine silver whereas the material in the ductal lamina is positive for mucicarmine and alcian blue. Immunohistochemical markers for the outer clear myoepithelial cells are S100, smooth muscle myosin, - actin and the ductal cells show positivity for keratin and amylase.
Electron microscopy confirms the dual cell population. Ductal cells adjacent to the lumen contain intracytoplasmic tonofilament bundles, well-formed desmosomes and atypical microvilli along the luminal border. Varying numbers of mitochondria, golgi apparatus, and rough endoplasmic reticlum are also seen. Outer myoepithelial cells, which lie within the external lamina, contain abundant glycogen and peripheral array of fine filaments with electron dense areas atypical for cells with smooth muscle differentiation. Basal lamina at stromal epithelial interface displays elaborate replication pattern  .
Foci of monomorphic biphasic structures composed of ductal and outer myoepithelial clear cells are usually encountered in pleomorphic adenoma, basal cell adenoma and adenoid cystic carcinoma. Clear cell change in the neoplastic myoepithelial cells in pleomorphic adenoma simulates the biphasic pattern of EMC  . EMC and pleomorphic adenoma intersect in terms of morphology and phenotypic expression since both express epithelial and myoepithelial differentiation. Therefore it is not surprising to encounter cases of EMC in pleomorphic adenoma, though the incidence is very rare.
No precise information regarding the effectiveness of various types of treatment for EMC is present. Surgery remains the primary mode of treatment. Simple enucleation and shelling out is avoided due to the possibility of local recurrence. Recurrence and metastases remain a concern and may occur a few months to years after initial surgery.
| Conclusion|| |
A case of EMC occurring in the palate of a 50-year-old male was presented with characteristic diagnostic features. This entity, though considered as a low-grade malignancy, requires regular follow up on account of its tendency to recur occasionally and metastasize to a distant site. Proper diagnosis is therefore of paramount importance.
| References|| |
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[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6]