|CLINICAL CASE REPORT
|Year : 2010 | Volume
| Issue : 2 | Page : 82-84
Myoepithelial carcinoma of the parotid gland arising in a pleomorphic adenoma: A case report
Fatma Homoud Al Anazy
King Saud University Medical College, Riyadh, Saudi Arabia
|Date of Web Publication||2-Jan-2020|
Source of Support: None, Conflict of Interest: None
Background: We describe an unusual salivary neoplasm, an epithelial-myoepithelial carcinoma of the parotid gland that occurred in a 36-year-old woman with a pleomorphic adenoma of the parotid gland.
Methods: The clinical, radiological, and hsitological findings of the patient are presented.
Results: The initial tumor was a pleomorphic adenoma with epithelial and myoepithelial elements. Subsequently the tumour recurred three times surgery was required and the patient refused radiotherapy with huge growth during 10 years of irregular follow up. Extensive, although good recovery occurred.
Conclusions: Although myoepithelial carcinomas (EMC) comprise approximately only 1% of all salivary gland tumours it should be suspected when there is recurrence in a pleomorphic adenoma .
Keywords: salivary gland; pleomorphic adenoma; myoepithelial carcinoma.
|How to cite this article:|
Al Anazy FH. Myoepithelial carcinoma of the parotid gland arising in a pleomorphic adenoma: A case report. Saudi J Otorhinolaryngol Head Neck Surg 2010;12:82-4
|How to cite this URL:|
Al Anazy FH. Myoepithelial carcinoma of the parotid gland arising in a pleomorphic adenoma: A case report. Saudi J Otorhinolaryngol Head Neck Surg [serial online] 2010 [cited 2022 Nov 30];12:82-4. Available from: https://www.sjohns.org/text.asp?2010/12/2/82/274639
| Introduction|| |
Pleomorphic adenoma or mixed tumour is the most common neoplasm of salivary gland origin and although malignant transformation is relatively uncommon it is well described.  The most common malignant tumour to arise in a pleomorphic adenoma is a carcinoma, usually undifferentiated carcinoma or adenocarcinoma not otherwise specified. The term epithelial-myoepithe- lial carcinoma was introduced in 1972 by Donath et al. , formerly referred to as a clear cell adenoma and adenomyoepithelioma. , Epithelial-myoepithelial carcinomas (EMC) comprise approximately 1% of all salivary gland tumours. The case study presented here is a myoepithelial carcinoma (malignant myoepithelioma) that arose in a pleomorphic adenoma of the parotid gland with multiple huge recurrences, irregular follow-up, and patients’ refusal of radiotherapy.
| Case Report|| |
A 36-year-old woman presented to our emergency room with a huge swelling of the left parotid and neck area. Her problem started in 1997 when she was diagnosed with a left parotid lesion that had been growing for 10 years. Superficial parotidectomy was performed at that time and demonstrated pleomorphic adenoma. Three years later, she had recurrence of the disease and underwent revision with complete parotidectomy but preservation of the facial nerve; the pathology report verified a myoepithelial carcinoma. The patient was referred for radiotherapy but she refused treatment and was lost to follow up.
Three years later, she had a second recurrence with a huge fungating, infected mass, skin involvement, and enlarged neck lymph nods in the left posterior triangle, with engulfment of the facial nerve by the tumour but no evidence of bone erosion and no metastases. She was also pregnant in the second trimester, and after delivery underwent left radical parotidectomy, facial nerve section, modified radical neck dissection, and a free skin flap. The histological report indicated recurrent myoepithelial carcinoma. Postoperatively the patient was referred again for radiotherapy but she refused treatment and was lost to follow up for 4 years. Until she reappeared in our emergency room with very huge mass in the left neck and parotid region with pain, there was no history of shortness of breath, weight loss, or anorexia. Examination revealed an oval-shaped mass measuring 15x12x10 cm in the left parotid area and neck that was firm, tender, with an irregular margin and surface, attached to the skin and the underlying tissue and had scars of previous surgeries [Figure 1]. There was an enlarged multiple cervical lymph node in the posterior triangle and complete left facial nerve palsy was present. The patient was admitted to the hospital. Computed tomography (CT) revealed a large, lobular, heterogeneous, soft tissue mass seen in the left side of the head and neck area attached to the level of the parotid down to the midcervical region with hypodense areas. The mass involved the adjacent masseter and sternocleidomastoid muscles, large multiple lymph nodes seen in the left posterior triangle, although the parapharyngeal fat planes were preserved [Figure 2]. The CT scan of the abdomen showed no metastases. MRI demonstrated a huge multiple mass that measured 11 x 11 x 8 cm with a signal intensity similar to muscles on T2-weighted signal intensity and heterogeneously hyperintense signals on T2-weighted signal intensity. The mass was superficial to the carotid sheath and abutted the left mandibular angle. However, neither definitive bone destruction nor appreciable normal parotid was identified. The mass was also closely related to the inferior surface of the external auditory canal and the adjacent skull base but no intracranial extension and evidence of lymphadenopathy in the left posterior triangle was evident. Ultrasound of the neck showed a huge, soft heterogeneous mass with some internal hypoechoic fluid area possibly representing necrotic changes seen in the left neck at the parotid level up to the lower neck region. Exact measurement of the mass could not be undertaken because of its huge size. The patient underwent left radical parotidectomy, left radical neck dissection with skin resection, and primary closure along with a left eyelid gold weight implant [Figure 3]. Her histopathology report showed a malignant spindle cell neoplasm with an infiltrative growth pattern and high mitotic rate; moreover, there was involvement of local lymph nodes. The immunophenotype was characteristic of myoepithe-lial differentiation: tumour cells stained positively with anticytokeratin antibodies, S-100 protein, smooth muscle actin, and vimentin. Electron microscopy confirmed myoepithelial differentiation, with small foci of keratinocytic phenotype. Large numbers of tumour cell nuclei were reactive with anti-p53 antibody DO-7 but were negative for soft-tissue margins and no invasion of skeletal muscles or veins were noted. Thirty-three lymph nodes were noted free of malignancy. Postoperatively the patient made a good recovery, and again postoperative radiotherapy was planned, but unfortunately, we lost her again and were unable to contact her.
|Figure 1: showing a huge mass in the left parotid area and neck with scars of the previews surgeries|
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|Figure 2: Computed tomography (CT) revealed large lobulated heterogeneous soft tissue mass seen in the left side of the head and neck area with hypodense areas|
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| Discussion|| |
Salivary gland neoplasms composed exclusively or predominantly of myoepithelial cells are relatively uncommon. Most behave in a benign fashion and are designated myoepithelioma. The malignant counterpart, myoepithelial carcinoma, is rare but may occasionally develop in a pre-existing pleomorphic adenoma and most often arises de novo.  The tumour is mainly composed of variable portions of ductal and clear- staining myoepithelial cells. EMC is predominantly a tumour of the major salivary glands, especially the parotid gland, but can also arise in minor salivary glands. , and rarely in extra-oral sites, such as the paranasal sinuses ,, pharynx  and bronchus . Tumours with histological features similar to EMC of the salivary gland have been identified in breast and skin as well ,.
EMC is primarily a tumour of adults, although tumours in children have been reported.  The peak incidence is in the seventh decade of life and the mean age of patients is about 60 years. About 60% of the patients are female; our patient had the disease when she was 26 years-old.
Two criteria must be satisfied to establish a diagnosis of myoepithelial carcinoma: the neoplastic cells must show myoepithelial differentiation and the tumour must be malignant. In the present case, myoepithelial differentiation was established by immunohistochemistry and electron microscopy. The immunophenotype was characteristic: tumour cells were immunoreactive with antibodies to cytokeratin (AEl/AE3), S-100 protein, and smooth muscle actin.
In this case study, malignancy clearly arose in a pleomorphic adenoma. In other cases, demonstration of a pre-existing adenoma may be more difficult, because the malignant tumour may overgrow and completely obliterate any residual benign elements. Most carcinomas arising from pleomorphic adenomas have the pattern of undifferentiated carcinoma or adenocarcinoma not otherwise specified ,. Rarer types include mucoepidermoid carcinoma, squamous carcinoma, adenoid cystic carcinoma, acinic cell carcinoma, and clear cell adenocarcinoma. ,.
It is important to consider a diagnosis of myoepithelial carcinoma when confronted with a malignant tumour arising in a pleomorphic adenoma. Most carcinomas arising in this situation are highly aggressive neoplasms; this may not be the case with myoepithelial carcinoma, which appears to be a low-grade malignancy when arising in a pleomorphic adenoma, but tends to be more aggressive and have a higher metastatic potential when arising de novo . Because of the tendency to local recurrence and the low metastatic potential, the tumour is now recognized as a low-grade malignant tumour in the WHO salivary gland classification . Our patient had the tumour for more than 10 years with 3 recurrences and no metastases. Deere et al.  reported a significant local recurrence rate of 42% in patients with EMC of the salivary glands. Metastases in 10% of cases, especially those to the periparotid and cervical lymph nodes, required a complete surgical resection as the only and best treatment for EMC followed by radiotherapy. However, adjuvant radiotherapy might be effective in preventing local recurrence . In the present case, the fact that a benign tumour was diagnosed in the left parotid gland 10 years earlier, and was later followed by a malignant tumour makes this case unique. The diagnosis of myoepithelial carcinoma should definitely be considered when one is confronted with a malignant tumour arising in a pleomorphic adenoma.
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[Figure 1], [Figure 2], [Figure 3]