Epithelial Myoepithelial Carcinoma-A Rare Case Report

Background: Salivary gland tumors occupy an imperative part while considering the entire spectrum of tumor pathology occurring in the maxillo-facial and cervical areas. They often pose diagnostic uncertainty due to intrinsic architectural and cytologic complexity, overlapping architecture. Epithelial-myoepithelial carcinoma is a rare tumor, constituting 1% of all salivary gland tumors. Methods and Results : We present a case of Epithelial-myoepithelial carcinoma in a 55-year-old male who presented with paresthesia of lower lip and swelling of the right side of face . Imaging revealed complete destruction of right ramus with an enhancing soft tissue mass. Patient underwent a surgical excision of the mass, which revealed an Epithelial-myoepithelial carcinoma. Conclusion : Although Epithelial-myoepithelial carcinoma is extremely rare in occurrence, have immense destructive capabilities. Hence a description of clinical presentation, radiographic extension and histopathologic presentation would be of great additive value to the sparse information of this rare tumor DOI:  http://dx.doi.org/10.3329/bjms.v11i2.11480 Bangladesh Journal of Medical Science Vol. 11 No. 02 April 2012: 129-133


Introduction
Salivary gland tumors occupy an imperative part while considering the entire spectrum of tumor pathology occurring in the maxillo-facial and cervical areas.They often pose diagnostic uncertainty due to intrinsic architectural and cytologic complexity, overlapping architecture amongst many benign and malignant tumors. 1 Carcinomas of the salivary glands are uncommon. 2Epithelial-myoepithelial carcinoma (EMC) is a rare malignant tumor, which constitutes approximately 1% of all salivary gland tumors.It was established as a distinct clinicopathologic entity by the World Health Organization in 1991. 3The major salivary glands, especially the parotid gland, are the most frequent site involved; however, cases arising in minor salivary glands and extraoral areas have also been reported. 4We report a case of EMC in a 55 year old male, and discuss the clinical, radiological, histopathological, and immunohistochemical findings.

Case Report
The WHO defined the EMC as a tumor composed of variable proportions of two cell types, an inner layer of duct-lining cells and an outer layer of clear cells, which typically form double-layered duct-like structures.Both electron microscopy and immunohistochemistry disclose that the outer clear cells are of myoepithelial origin. 5 The most prevalent site of occurrence of EMC is the major salivary glands, especially in the parotid gland.Around 10% of this type of tumour has its origin in the submandibular gland and between the 10-15% in the minor salivary glands. 6Some studies have reported that the intercalated duct in the minor salivary gland is lacking or shorter than that in the parotid gland.This may explain why most EMCs occur in the major salivary glands.However, it is unknown why EMCs occur more commonly in the parotid gland than the submandibular gland.This difference may be related to variations in the intercalated ducts in the two sites. 3 The etiological factors for salivary tumors are not clearly defined. 2 As in other salivary gland neoplasms, there is a female predominance, with a female-to-male ratio of approximately 2:1.Most patients affected are adults in the sixth or seventh decade of life, although rare cases have been described in children and adolescents.The most common clinical presentation is a slowly enlarging mass.Occasionally, pain or facial weakness may be present.The mean tumor size is 2-3 cm, with a range from 1 to 12 cm in largest dimension. 1The lesion may be encapsulated, but the capsule is frequently incomplete and tumor nodules often extend through it. 5In the present case tumor was partially encapsulated.Gross haemorrhage and necrosis are uncommon.

1
CT and MR appearances of EMC are nonspecific, and EMC cannot be differentiated from other parotid neoplasms. 4In this case CT and MRI study indicated that the mass was in the right submasseteric space abutting the parotid gland posteriorly while draped over by the masseter laterally and compressing the medial pterygoid thus suggesting a possible site of origin as extracapsular gland tissue from parotid or accessory parotid.CT and MR imaging of the lesion showed complete destruction of the right ramus indicating a malignant aggressive tumor but this did not correlate with the histological findings of a low grade malignant lesion.Morphologically EMC express both epithelial and myoepithelial differentiation.Tumor presents as bulky, lobulated, slowgrowing mass becoming large.Tumor myoepithelial phenotype has been cited as a reason why tumors generally grow in a bulky lobulated fashion, rather than in infiltrating pattern.Rarely, some epithelial-myoepithelial carcinoma may be found in combination with other salivary gland tumors forming hybrid carcinoma or show dedifferentiation.

8, 9
Although some studies have characteristically described the ductal cells as being positive for cytokeratin and the clear cells as immunoreactive for S-100 protein 10 , this description is relative.
Reactivity for S-100 protein is variable.
1 Surgical excision with wide margins is indicated as the first choice for treatment because of the locally invasive behavior of these tumors. 11A wide margin was given while excision was carried out for the present case.
Most studies indicate that EMC is a low-grade malignancy with local recurrence found in 23% to 50% of cases, lymph node metastases in 17% to 23%, and distant metastases to lung, kidney and brain in up to8-l0% and with fatal outcome in up to 8-l0%. 1, 12 the 5-year-survival rate is 67%.The prognosis is bad in tumors having a diameter of 4 cm or more and for those solid tumors predominantly composed of clear cells, forming nests and sheaths. 12In presenting case, patient had no loco regional recurrence.

Conclusion
Although Epithelial-myoepithelial carcinoma is extremely rare in occurrence, have immense destructive capabilities.Hence a description of clinical presentation, radiographic extension and histopathologic presentation would be of great additive value to the sparse information of this rare tumor.

Figure I :
Figure I: Photograph of patient depicting the extent of swelling.

Figure III :
Figure III: Axial CT scan showing complete erosion of ramus of right mandible also notice mass infiltrating into the ipsilateral masseter muscle.Figure V: Photograph showing surgical exploration of the site.

Figure V :
Figure III: Axial CT scan showing complete erosion of ramus of right mandible also notice mass infiltrating into the ipsilateral masseter muscle.Figure V: Photograph showing surgical exploration of the site.

Figure IV :
Figure IV: Axial MRI section showing expansile lytic lesion with heterogeneously enhancing solid soft tissue involving right ramus, condyle and coronoid process of mandible.

Figure II :
Figure II: Orthopantomogram showing complete destruction of right ramus and residual right condyle.

Figure
Figure VI (A): Photomicrograph (100X resolution, Haemotoxyline & Eosin) showing partially encapsulation, lesional cells in lobular pattern, occasional infiltration of connective tissue and cuboidal and columnar cells attempting to form duct-like structures.