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Year : 2014  |  Volume : 57  |  Issue : 1  |  Page : 85-88
Myoepithelial carcinoma of palate: Case report

Department of Oral and Maxillofacial Pathology, Sathyabama University Dental College and Hospital, Chennai, India

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Date of Web Publication17-Apr-2014


Myoepithelial carcinoma is an uncommon malignant salivary gland neoplasm with a predilection for parotid gland. However, its occurrence in minor salivary glands is considerably less with only 28 cases being reported in the literature. We report a case of myoepithelial carcinoma of palate in a 50-year-old woman. Computed tomography and magnetic resonance imaging revealed an extensive lesion in the palate. Microscopically, the tumor exhibited a wide spectrum of cytomorphologic features that overlap with other salivary gland tumors. Immunohistochemistry served as an adjunct in the diagnosis of the lesion. Clinical, radiographic, and histopathologic correlation along with immunohistochemical profile enabled to arrive at a diagnosis of myoepithelial carcinoma.

Keywords: Myoepithelial carcinoma, minor salivary gland tumor, palate

How to cite this article:
Thayumanavan B, Vani NV. Myoepithelial carcinoma of palate: Case report. Indian J Pathol Microbiol 2014;57:85-8

How to cite this URL:
Thayumanavan B, Vani NV. Myoepithelial carcinoma of palate: Case report. Indian J Pathol Microbiol [serial online] 2014 [cited 2021 Oct 21];57:85-8. Available from: https://www.ijpmonline.org/text.asp?2014/57/1/85/130906

   Introduction Top

Myoepithelial carcinoma (malignant myoepithelioma) is defined as a malignant salivary gland neoplasm that is composed almost exclusively of tumor cells with myoepithelial differentiation. [1] Although it was first described by Stromeyer et al. in 1975, [2] this entity was included in the world health organization (WHO) classification of salivary gland neoplasm later in 1991. [3] It is an uncommon malignancy of the minor salivary glands accounting for less than 1% of tumors of this origin. [3]

Myoepithelial carcinoma arises predominantly from the major salivary glands, either de novo or as a carcinoma arising from a preexisting pleomorphic adenoma or myoepithelioma. A thorough literature search based on Pubmed and medline revealed only 28 cases being reported in the intraoral minor salivary glands. [4],[5],[6],[7],[8],[9],[10],[11],[12],[13],[14],[15],[16],[17],[18],[19],[20],[21],[22],[23],[24] Myoepithelial carcinomas exhibit a wide spectrum of cytomorphologic features which make them easily confused with other salivary gland tumors. Awareness of their unique cytoarchitectural patterns and immunohistochemical profile is crucial for accurate diagnosis. We present a case of myoepithelial carcinoma of palate that showed diverse cytomorphologic and architectural features.

   Case Report Top

A 50-year-old female patient presented to the dental clinic with a complaint of slowly growing painless mass in the left palate since seven years. On examination, the growth was nodular and firm measuring about 5 × 4 cm, extending from upper left canine region to maxillary tuberosity. Mediolaterally, it extended from the midline of palate to left buccal vestibule . The surface of the growth was smooth and covered by normal mucosa [Figure 1]a. Physical examination showed no evidence of lymphadenopathy and distant metastasis.

Orthopantomogram showed well-defined periapical radiolucency in relation to upper left first molar region involving the left maxillary antrum, measuring about 6 × 5 cm in size and extended superiorly up to the zygomatic arch, inferiorly involving the alveolar margin of upper left posterior edentulous area, while medially it extends from the periapical region of upper left first premolar region till the coronoid process laterally [Figure 1]b. Computed tomography and magnetic resonance imaging of maxillary region revealed ill-defined heterogeneous expansile soft tissue attenuation lesion involving left maxillary antrum with expansion and destruction of anterior, medial, and posterolateral wall. Multiple hypodense areas suggestive of possible necrosis were also noted. The lesion also extended to involve the alveolar processes of left maxilla causing destruction from upper left premolar to second molar region and also involved the inferior part of left pterygoid bone, left medial pterygoid muscle, and lateral part of hard palate [Figure 1]c. Hematological evaluation was found to be within normal limits. Incisional biopsy was done and a histopathologic diagnosis of adenocarcinoma was rendered and advised for postoperative evaluation. The patient underwent wide surgical excision of the tumor under general anesthesia. Postoperative course was uneventful.
Figure 1: (a) Nodular growth in the left palate. (b) Panoramic radiograph showing well-defined periapical radiolucency in relation to upper left first molar region involving the left maxillary antrum. (c) CT scan
showing ill-defined heterogeneous expansile soft tissue attenuation lesion

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Grossly, the resected tumor was poorly circumscribed and invaded the adjacent normal tissue. The tumor was soft to slightly firm in consistency with a gray white cut surface and few hard calcified areas. Obvious areas of necrosis and hemorrhage were also noted. Microscopically, the tumor exhibited solid architecture with cells being arranged in multiple nodules, nests, and sheets [Figure 2] a, b]. Moreover, the tumor cells had a diverse morphology: epitheloid cells being round to polygonal in shape with variable amount of eosinophilic cytoplasm [Figure 2]c; clear cells with clear cytoplasm and well-defined cell borders [Figure 2d]; spindle cells with eosinophilic or pale cytoplasm [Figure 2e]; and plasmacytoid cells with brightly eosinophilic cytoplasm and eccentric nuclei [Figure 2f]. The clear cells were predominantly arranged in a lobular pattern with minimal intervening stroma. The tumor-related matrix was mostly hyalinized [Figure 3]a with focal areas of wiry fibrillary stroma, collagenous crystalloids, and myxoid stroma [Figure 3]b-d]. Occasional areas of necrosis and calcifications were also present [Figure 3]e, f]. Moderate cytologic atypia was noted with nuclear enlargement, vesicular or coarse chromatin, and variably prominent nucleoli. Mitotic figures ranged from 2 to 4 per 10 high power fields. Immunohistochemical staining showed positive reactivity for cytokeratin, S100, p63, GFAP, and vimentin. 10 to 15% of the cells exhibited strong positivity for Ki-67 [Figure 4] a-f]. Based on clinical, radiographic, histopathologic, and immunohistochemical correlation, a diagnosis of low-grade myoepithelial carcinoma was rendered. The patient was treated successfully with wide local surgical excision. The postoperative course was uneventful and patient remained free of disease for a follow-up period of one year.
Figure 2: (a) Epitheloid cells showing multinodular architecture (×40). (b) Lobular arrangement of clear cells with intervening hyalinized matrix (×100). (c) Epithelioid cells (×400). (d) Clear cells (×400). (e) Spindled cells (×400). (f) Plasmacytoid cells (×400)

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Figure 3: (a) Hyalinized stroma (×100). (b) Wiry and fibrillary stroma (×400). (c) Collagenous crystalloids (×100). (d) Myxoid stroma (×400). (e) Necrosis (×100). (f) Calcifications (×100)

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Figure 4: Immunohistochemical staining showed (a) Intense cytoplasmic positivity for cytokeratin (×400). (b) Strong positivity for S100 (×400). (c) Strong diffuse staining for p63 (×400). (d) Positive immunostaining for GFAP (×400). (e) 10-15% of cells exhibiting positive nuclear staining for Ki-67, (×400). (f) Strong positivity for vimentin (×400)

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   Discussion Top

Myoepithelial carcinoma is defined as "neoplasm composed almost exclusively of tumor cells with myoepithelial differentiation and characterized by infiltrative growth with potential for metastasis." [25] It is considered to be an uncommon tumor of minor salivary glands and has been under recognized in the past as majority of them arise in pleomorphic adenomas and were either categorized into a rather broad category of malignant mixed tumor or carcinoma ex-pleomorphic adenoma. [15] Most cases occur in the age range of 14 to 77 years with an average age of 57 years. [24] There was a female predominance with a male to female ratio of 0.87:1. [24] Intraorally, palate was involved in about 60% of cases. [24] The tumor most commonly presented as an intraoral swelling with occasional surface ulceration, pain, or bleeding. Similar to the reported cases, even the present case also occurred in a 50-year-old female patient presenting as a painless nodular mass in the left palate.

Morphologic heterogeneity is the hallmark of neoplastic myoepithelial cells, as they display a wide range of cytological features that varies from epitheloid, hyaline, clear, spindle, or mixed cell types. [25],[26] The most common cell types encountered in our case were epitheloid, clear, and spindle cells whereas only few plasmacytoid cells were present. This is in contrast to the observations made by Savera et al., [15] where the spindle cell variants are least common compared to other cell types.

Myoepithelial carcinoma also displays a wide range of histological features with a variable amount of matrix and architectural patterns ranging from reticular, trabecular, and solid pattern. Another typical feature of this tumor which was also noted in this case is the presence of multinodular architecture with hypercellular peripheral rims and hypocellular myxoid or necrotic centers. [15] A plausible explanation for this feature is that the neoplastic myoepithelial cells secrete low amount of matrix degrading proteinases and large amount of proteinase inhibitors in addition to abundant extracellular matrices. [27] This pattern of central necrosis is similar to that of comedo necrosis seen in salivary duct carcinomas. The present case had mostly hyalinized stroma with focal areas of myxoid and wiry fibrillary stroma which is in contrary to the findings made by Savera et al. [15] Few calcified areas were also observed. Another noteworthy feature was the presence of collagenous crystalloids and intercellular hyaline material, as described by Ska'lova et al. [28]

The cytomorphologic heterogeneity of myoepithelial cells and the overlapping histopathologic features of myoepithelial carcinoma pose diagnostic difficulties at times. However, the diagnosis of myoepithelial carcinoma is based on two main histological criteria: exclusive myoepithelial differentiation and unequivocal evidence of malignancy. [15] Immunohistochemistry is considered to be the best method for identification of myoepithelial cells. Immunoreactivity for cytokeratins and at least one of the myoepithelial markers which includes vimentin, calponin, S100, p63, glial fibrillary acidic protein, SMA, and smooth muscle heavy chains are considered to be of diagnostic value. [1] The neoplastic cells in the present case showed positive immunoreactivity for cytokeratin, S100, p63, GFAP, and vimentin.

The infiltrating growth pattern along with the presence of mitotic figures and necrosis helps to distinguish myoepithelial carcinoma from its benign counterpart. Traditionally, the histologic features that are considered helpful in discriminating benign and malignant myoepitheliomas include cytologic atypia, tumor infiltration, and mitotic rate. [29] According to Savera et al., [15] tumor infiltration into adjacent tissue is considered as a minimum requirement for myoepithelial carcinoma. The low-grade myoepithelial carcinomas can masquerade as myoepithelioma or pleomorphic adenoma, since most of these carcinomas arise in an adenoma and infiltrate as nodular aggregates or finger-like extensions. Moreover, they lack significant cytologic atypia and identification of tissue infiltration can be the only indication of their aggressive biologic behavior. Therefore, the presence of distinct multinodularity and extension into adjacent tissues should raise a suspicion of malignancy. Mitotic figures and necrosis that are not typically seen in pleomorphic adenomas and myoepitheliomas are also helpful in supporting the diagnosis. Even the present case exhibits nodular infiltration into adjacent tissues along with features such as cytologic atypia, necrosis, and mitotic figures suggestive of a malignant tumor.

Recently, it has been suggested that assessment of cell proliferative activity may be helpful in the differential diagnosis of benign and malignant myoepitheliomas, and a Ki-67 labeling index of more than 10% is diagnostic of myoepithelial carcinoma. [12] 10 to 15% of the cells showed strong positivity for ki-67 in our case, suggesting high cellular proliferative activity.

In conclusion, we present a case of low-grade myoepithelial carcinoma of intraoral minor salivary gland which is an uncommon tumor. Awareness of the clinicopathological and immunohistochemical features of these lesions is crucial for accurate diagnosis and proper treatment. Wide local excision with tumor-free margins is the preferred treatment of choice.

   References Top

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Correspondence Address:
Nandimandalam Venkata Vani
Department of Oral and Maxillofacial Pathology, Sathyabama University Dental College & Hospital, Chennai - 600 119
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0377-4929.130906

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