Mucoepidermoid carcinoma

Mucoepidermoid carcinoma (MEC)^[1] is the most common type of minor salivary gland malignancy in adults. Mucoepidermoid carcinoma can also be found in other organs, such as bronchi, lacrimal sac,^[2] and thyroid gland.

Mucoepidermoid carcinoma
Micrograph of a mucoepidermoid carcinoma. FNA specimen. Pap stain.
Specialty	Oncology, Maxillofacial surgery, ENT surgery

Mucicarmine staining is one stain used by pathologist for detection.^[3]

Signs and symptoms

Presents as painless, slow-growing mass that is firm or hard. Most appear clinically as mixed tumors. Usually occurs at 30–50 years of age. More predilection towards female sex.^{[citation needed]}

Diagnosis

Histology

This tumor is not encapsulated and is characterized by squamous cells, mucus-secreting cells, and intermediate cells.^[4]

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  Histopathologic image of mucoepidermoid carcinoma of the major salivary gland. H & E stain
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  Histopathologic image of mucoepidermoid carcinoma of the major salivary gland. The same lesion as shown in a filename "Mucoepidermoid carcinoma (2) HE stain.jpg". H & E stain
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  Histopathologic image of mucoepidermoid carcinoma. Postoperative recurrence of the submandibular tumor. Alcian blue-PAS stain

Molecular biology

Mucoepidermoid carcinomas of the salivary and bronchial glands are characterized by a recurrent t(11;19)(q21;p13) chromosomal translocation resulting in a MECT1-MAML2 fusion gene.^[5] The CREB-binding domain of the CREB coactivator MECT1 (also known as CRTC1, TORC1 or WAMTP1) is fused to the transactivation domain of the Notch coactivator MAML2.^[6]

A possible association with radiation exposure has been reported.^[7] It has also been proposed that mucoepidermoid tumors arise from subepithelial mucous glands of the upper respiratory or digestive tracts.^[8]

Prognosis

Generally, there is a good prognosis for low-grade tumors, and a poor prognosis for high-grade tumors, however recent research have found reoccurring low grade tumors also have a poor prognosis.^[9]

Treatment

Surgery is the recommended treatment for localised resectable disease.^[10] When the tumour is incompletely resected (positive margins) post-operative radiotherapy gives local control comparable to a complete resection (clear margins).^[11]

Sometimes when surgery is not possible due to extent of disease or if a patient is too frail for surgery, or declines surgery, palliative radiotherapy may be helpful. There has been a report of a case where low dose radiotherapy achieve disease response and control for more than 4 years.^[12]

In patients with metastatic disease, chemotherapy response tends to be low (27% partial response rate) and short lived.^[13]

Epidemiology

Occurs in adults, with peak incidence from 20–40 years of age. A causal link with cytomegalovirus (CMV) has been strongly implicated in a 2011 research.^[14]

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  Relative incidence of parotid tumors, showing mucoepidermoid carcinoma at top right.^[15]
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  Relative incidence of submandibular tumors, showing mucoepidermoid carcinoma at top right.^[15]