|Year : 2014 | Volume
| Issue : 2 | Page : 53-56
Myoepithelioma of parotid: A case report and review of literature
Akhil Kapoor1, Prakash Singh Rajput2, Puneet Kumar Bagri1, Surender Beniwal3, Vanita Kumar2, Harvindra Singh Kumar1
1 Department of Radiation Oncology, Acharya Tulsi Regional Cancer Treatment and Research Institute, Sardar Patel Medical College and Associated Group of Hospitals, Bikaner, Rajasthan, India
2 Department of Pathology, Acharya Tulsi Regional Cancer Treatment and Research Institute, Sardar Patel Medical College and Associated Group of Hospitals, Bikaner, Rajasthan, India
3 Department of Medical Oncology, Acharya Tulsi Regional Cancer Treatment and Research Institute, Sardar Patel Medical College and Associated Group of Hospitals, Bikaner, Rajasthan, India
|Date of Web Publication||10-Mar-2015|
Department of Radiation Oncology, Acharya Tulsi Regional Cancer Treatment and Research Institute, Sardar Patel Medical College and Associated Group of Hospitals, Bikaner, Rajasthan
Source of Support: None, Conflict of Interest: None
Myoepithelioma (ME) is a rarely encountered tumor of salivary gland accounting for about 1% of all salivary gland tumors. Though they were first identified long back, still their histopathologic features and immunohistochemistry (IHC) profile are not well characterized and there is no definitive criterion for this tumor with complex and varied features remaining a major barrier. We present a case of parotid enlargement in an 18-year-old girl in whom the IHC studies of superficial parotidectomy specimen revealed positive staining for Cytokeratin 5/6, HMW CK, Smooth muscle actin (SMA), S100, calponin, vimentin, and p63. CD45, EMA, CK7, carcinoembryonic antigen (CEA), BerEP4, GCDFP-15, and Glial fibrillary acidic protein (GFAP)-stained negative. With these IHC findings, the diagnosis of ME of parotid was established. This report highlights the importance of IHC studies along with a brief review of the literature.
Keywords: Histopathology, immunohistochemistry, myoepithelioma, parotid
|How to cite this article:|
Kapoor A, Rajput PS, Bagri PK, Beniwal S, Kumar V, Kumar HS. Myoepithelioma of parotid: A case report and review of literature. J Oral Res Rev 2014;6:53-6
|How to cite this URL:|
Kapoor A, Rajput PS, Bagri PK, Beniwal S, Kumar V, Kumar HS. Myoepithelioma of parotid: A case report and review of literature. J Oral Res Rev [serial online] 2014 [cited 2022 Aug 15];6:53-6. Available from: https://www.jorr.org/text.asp?2014/6/2/53/152910
| Introduction|| |
Myoepithelial cells are present in the acini and intercalated ducts of salivary glands normally. As the name suggests, these cells express a dual epithelial and smooth muscle phenotype.  Myoepithelioma (ME) is a rarely encountered tumor of salivary gland accounting for about 1% of all salivary gland tumors.  Besides involving the major salivary glands, it may be also found in the palate arising from minor salivary glands. Though most of the times, they are benign, recurring only in cases where incomplete surgical resection was done, there have been few cases with malignant histology as well. The pathologist and treating oncologist should be aware of this rare diagnosis, and it should always be a part of the differential diagnosis. However, only morphological examination may be insufficient even for an experienced pathologist in some cases. In such a case, the role of immunohistochemistry (IHC) studies comes into play and it should be contemplated to clinch the diagnosis. We present a case of benign ME of parotid in an 18-year-old girl diagnosed after IHC studies describing the importance of the same along with a brief review of the literature.
| Case Report|| |
An 18-year-old girl presented with a four-month history of gradually progressive, painless swelling in the left pre-auricular region. On palpation, a 4 cm Χ 3 cm swelling, mobile, smooth surfaced, and well-defined margins. There were no signs of facial nerve palsy or cervical lymphadenopathy. There were no associated comorbidity or significant past history. Contrast-enhanced computed tomography of the neck revealed a well-circumscribed, lobulated mass lesion in the left parotid gland with inhomogeneous enhancement. Fine needle aspiration cytology (FNAC) of the lesion suggested poorly differentiated carcinoma. A left superficial parotidectomy was performed while preserving the facial nerve and the tumor was enucleated. On gross examination, a solid tumor with a slightly reddish hue was visible. It measured 4 cm Χ 3 cm Χ 2.5 cm. The morphology of the sections showed tumor and pieces of salivary gland tissue. The tumor was composed of irregular but well defined masses of oval to short spindle cells. They had oval to elongated nuclei, dispersed chromatin, a definite but small nucleolus and ill-defined pale eosinophilic to clear cytoplasm [Figure 1]. No definite diagnosis could be reached. To clear the diagnostic dilemma, IHC studies were performed. Cytokeratin 5/6 [Figure 2]a], HMW CK [Figure 2]b], Smooth muscle actin (SMA) [Figure 3]a], S100 [Figure 3]b], calponin, vimentin, and p63 [Figure 3]c] stained positive. CD45, EMA, CK7, carcinoembryonic antigen (CEA), BerEP4, GCDFP-15, and Glial fibrillary acidic protein (GFAP)-stained negative. The IHC pattern along with the morphology favored the diagnosis of ME of the parotid. The postoperative course was uneventful and no adjuvant therapy was prescribed. The patient was symptom free after two years of surgery.
|Figure 1: Photomicrograph showing irregular but well defined masses of oval to short, spindle cells differently interlaced, with eosinophilic cytoplasm. [H&E, (a) 4×, (b) 25×]|
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|Figure 2: Photomicrograph showing positive staining for (a) cytokeratin and (b) High molecular weight cytokeratin (4×)|
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|Figure 3: Photomicrograph showing positive staining for (a) Smooth muscle actin, (b) S100, and (c) p63 (4×)|
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| Discussion|| |
Salivary gland tumors composed entirely of myoepithelial cells are unusual in clinical practice. They have been known for a long time, with Sheldon classifying three tumors as ME in 1943 while reviewing 57 mixed tumors of the salivary glands.  Still, their histopathologic features and IHC profile are not well characterized and there is no definitive criterion for this tumor with complex and varied features remaining a major barrier.
Equal gender distribution is usually seen; however, an analysis of 15 cases arising in the minor salivary glands of the palate demonstrated a 2:1 female preponderance.  The mean age of presentation is about 44 years, with a wide range from 9 to 85 years.  The patient in our report is a young 18-year-old girl. The parotid gland is the usual site in 40-50% cases,  followed by the minor salivary glands located in the palate (21%),  while the submandibular gland is the primary site in 10% of the cases. The usual presentation of ME is a painless, slow-growing mass with intact facial nerve function.
On gross examination, ME are well-circumscribed, gray-white or yellow solid masses with a smooth surface without any degenerative changes. [7,8] There are four main cell morphologies: Spindle, epithelioid, plasmacytoid, and clear cells. The spindle cell histology is the most common one and was the one in our report, while there can be a mixture of them in a single tumor. Spindle cell ME has central fusiform nuclei with eosinophilic cytoplasm and tapered ends arranged in an interlacing fascicle. In epithelioid cell ME, large polygonal cells with central nuclei and eosinophilic cytoplasm are present. They can sometimes form pseudoacini/pseudoglandular structures. In plasmacytoid cell ME, cells are round to ovoid with abundant eosinophilic cytoplasm and eccentric nuclei. This cell type is frequently found in palatal ME. Clear cell ME are the rarest one and have polygonal cells with clear cytoplasm ascribed to glycogen content. Trabecular, nested, or solid architectural patterns may be seen.
It is also important for the pathologist to distinguish between myoepithelial-rich pleomorphic adenoma and ME by noting the complete absence of ductal elements.  On electron microscope examination, the myoepithelial cells contain abundant cytoplasmic filaments and basement membranes are duplicated, plaques attached to the cell membrane, perinuclear tonofilament bundles and desmosome-type intercellular junctions. 
The IHC studies have assumed great importance to confirm this complex and rare diagnosis. ME cells are usually positive for cytokeratins (e.g., AE1/AE3, CK 5/6, Cam 5.2, CK-7, and CK-14) and vimentin. Vimentin is positive only in the neoplastic myoepithelial cells while negative in normal myoepithelial cells. Calponin has been designated as the most sensitive myogenic marker.  S-100 is often positive in the neoplastic myoepithelial cells but negative in normal salivary gland myoepithelial cells. SMA, Muscle-specific actin (MSA), Smooth muscle myosin, P63 protein, and GFAP are also usually positive. However, GFAP was negative in our patient. Due to the neoplastic transformation of myoepithelial cells, there can be modification in the smooth muscle phenotype resulting in variable positivity for the markers.  ME cells are characteristically negative for CEA due to the absence of tubular differentiation. Hornick et al. reported that ME cells with the morphology of spindle cell have the strongest immunoreactivity to markers for smooth muscle, followed by the epithelioid cells, with the plasmacytoid and clear cells demonstrating reduced activity.  Hence, a combination of these markers is necessary to clear the diagnostic dilemma. A rough criterion for IHC being the combination of a keratin along with the positivity for S-100, vimentin and one more myogenic marker for stamping the diagnosis of a ME.
Alterations in chromosome 1, 9, 12, and 13 have been reported.  Dysregulation of the p16INK4a pathway is also implicated in the development of ME and additional inactivation of p53 has been noted in the benign recurrences.  ME have been demonstrated to be less prone to recurrence after complete resection.  The standard of care being complete surgical excision preserving the facial nerve.
| Conclusion|| |
ME is a rare clinical entity and must be diagnosed correctly by appropriate IHC studies. It should be considered in the differential diagnosis of a parotid mass to facilitate the correct diagnosis.
| Acknowledgements|| |
The authors would like to thank consultants in department of Oncology Dr. Ajay Sharma, Dr. Neeti Sharma, Dr. S L Jakhar and Dr. MR Baradia.
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[Figure 1], [Figure 2], [Figure 3]