Mucoepidermoid carcinoma overview

# Overview
Mucoepidermoid carcinoma (also known as "Salivary gland mucoepidermoid carcinoma") is a malignant salivary gland tumor that consists of epidermoid and mucin producing cells. Mucoepidermoid carcinomas arise from mucous cells, which is normally involved in the secretion of mucous and the protection of surrounding tissue. Mucoepidermoid carcinoma is the most common malignant salivary gland tumor, and usually occurs in the parotid and submandibular salivary glands. Mucoepidermoid carcinomas may be classified according to location into 2 subtypes: salivary gland confined carcinomas and other organ mucoepidermoid tumors. The majority of these tumors present as parotid gland mucoepidermoid carcincoma lesions (65%). Development of mucoepidermoid carcinoma is the result of an abnormal production of mucin by mucus-secreting cells. Genes involved in the pathogenesis of mucoepidermoid carcinoma include MECT1 and MAML2 fusion genes. Mucoepidermoid carcinomas are usually found in middle aged adults between the second and sixth decade of life. Males are slightly more affected with mucoepidermoid carcinoma than females. The incidence of mucoepidermoid carcinoma is approximately 2.5 to 3.0 cases per 100,000 individuals a year. If left untreated, progression occurs slow and is then followed by sentinel lymph node metastasis. The treatment choice for mucoepidermoid carcinoma is surgical removal.

# Historical Perspective
Mucoepidermoid carcinoma was first described by Masson and Berger, two American pathologists, in 1924.

# Classification
Mucoepidermoid carcinoma may be classified according to location into 2 subtypes: salivary gland-confined carcinomas and other organ mucoepidermoid carcinomas.

# Pathophysiology
Mucoepidermoid carcinomas arise from mucous cells, which are normally involved in the secretion of mucous and the protection of the surrounding tissue. 
The pathogenesis of mucoepidermoid carcinoma consists of abnormal production of mucin from mucous cells, associated with the aberrant overgrowth of squamous and epidermoid cells. Genes involved in the pathogenesis of mucoepidermoid carcinoma include the MECT1 and MAML2 fusion genes. On gross pathology, mucoepidermoid carcinomas have a cystic, solid or mixed appearance, are normally located on the parotid or submandibular gland, and range in size from 1 to 8 cm. On microscopic histopathological analysis, mucoepidermoid carcinomas are characterized by mucous cells with abundant fluffy cytoplasm and large mucin vacuoles.

# Causes
There are no established direct causes for mucoepidermoid carcinoma. The development of mucoepidermoid carcinoma has been associated with the result of multiple genetic mutations in the MECT1 and MAML2 fusion genes.

# Differentiating Mucoepidermoid Carcinoma from other Diseases
Mucoepidermoid carcinoma must be differentiated from other diseases that cause painless swelling, facial deformity, and facial numbness, such as Warthin tumour, adenoid cystic carcinoma, benign mixed tumor, and metastasis.

# Epidemiology and Demographics
Mucoepidermoid carcinoma is the most common malignant salivary gland tumor among general population. The incidence of mucoepidermoid carcinoma is approximately 2.5 to 3.0 cases per 100,000 individuals a year. The incidence of mucoepidermoid carcinoma increases with age. The median age at diagnosis is between 20 to 50 years. Males are slightly more affected with mucoepidermoid carcinoma than females. There is no racial predilection for mucoepidermoid carcinoma.

# Risk Factors
Common risk factors in the development of salivary gland tumors include: ionizing radiation and occupations associated with an increased risk such as rubber products manufacturing, asbestos mining, plumbing, and some types of woodworking.

# Screening
According to the U.S. Preventive Service Task Force (USPSTF), there is insufficient evidence to recommend routine screening for mucoepidermoid carcinoma.

# Natural History, Complications and Prognosis
If left untreated, patients with mucoepidermoid carcinoma may progress to develop sentinel metastasis to adjacent lymph nodes. Common complications of mucoepidermoid carcinoma include facial deformity, difficulty swallowing, and local lymph node metastasis. Prognosis will generally depend on the clinical stage, tumor size, and histological grade. The overall recurrence rate will depend on the stage. Low grade tumors have a 90-98% survival rate and a low rate of local recurrence.

# Diagnosis

## Staging
According to the American Joint Committee on Cancer (AJCC) 7th edition, there are 6 stages of mucoepidermoid carcinoma based on the tumor size and node invasion. Each stage is assigned a letter and a number that designate the tumoral size and node invasion.

## History and Symptoms
The hallmark symptom of mucoepidermoid carcinoma is painless swelling. A positive history of cancer may be suggestive of mucoepidermoid carcinoma. Symptoms related with mucoepidermoid carcinoma will vary depending on the size and location of the tumor. Common symptoms of mucoepidermoid carcinoma may include facial numbness, adjacent muscle soreness, mandible claudication, otorrhea, dysphagia, and trismus.

## Physical Examination
Physical examination findings of mucoepidermoid carcinoma depend on the size and location of the tumor. Physical examination of patients with mucoepidermoid carcinoma is usually remarkable for tenderness and intraoral bluish-red mucosa.

## Laboratory Findings
There are no diagnostic laboratory findings associated with mucoepidermoid carcinoma.

## X Ray
On conventional radiography, there are no characteristic findings of mucoepidermoid carcinoma.

## CT
On CT scan, characteristic findings of mucoepidermoid carcinoma include: well-circumscribed masses, usually with cystic components (low-grade tumors), enhancements of solid components, and calcification. High-grade tumors have poorly defined margins, infiltrate locally, and appear solid.

## MRI
On MRI, characteristic findings of mucoepidermoid carcinoma will depend on the stage. Common findings include: low signal cystic spaces in T1 and  high signal in cystic areas on T2.

## Ultrasound
On ultrasound, characteristic findings of mucoepidermoid carcinoma include: a well-circumscribed hypoechoic lesion with a partial or completely cystic appearance, in contrast to the relatively hyperechoeic normal parotid gland.

## Other Imaging Findings
There are no other imaging findings associated with mucoepidermoid carcinoma.

## Other Diagnostic Studies
Other diagnostic studies associated with mucoepidermoid carcinoma may include: fine needle aspiration biopsy and incisional biopsy.

# Treatment

## Medical Therapy
There is no medical treatment for mucoepidermoid carcinoma. Radiotherapy can be neoadyuvant treatment in some lesions (dependent on the tumor stage and size).

## Surgery
Surgery is the mainstay of therapy for mucoepidermoid carcinoma.

# Primary Prevention
There is no primary prevention for mucoepidermoid carcinoma.

# Secondary Prevention
There is no secondary prevention for mucoepidermoid carcinoma.