What are the other Names for this Condition? (Also known as/Synonyms)

• Benign Ectomesenchymal Chondromyxoid Tumor
• Benign Myoepithelial Tumour
• Benign Parachordoma

What is Benign Myoepithelioma? (Definition/Background Information)

• Benign Myoepithelioma is an uncommon soft tissue tumor of myoepithelial cells. It is similar to salivary gland myoepithelial tumors showing same histological features (morphology). It is also known as a Benign Myoepithelial Tumor
• It can be present in individuals of a wide age range (including children and adults). The risk factors for Benign Myoepithelioma are not well-understood
• The cause of formation of Benign Myoepithelioma is reported to be due to certain chromosomal alterations and gene mutations. The involvement of EWSR1 gene is observed in about 45% of the myoepithelial tumors
• Most tumors are solitary, small, and painless, though the larger ones may compress the surrounding structures and cause related signs and symptoms. Most myoepitheliomas are found on the limbs (arms and legs)
• The diagnosis of Benign Myoepithelioma can be confirmed through a tissue biopsy. The treatment is a complete surgical removal of the tumor with adequate margins
• The prognosis of Benign Myoepithelial Tumor is generally excellent with adequate treatment (complete removal through surgery). However, tumor recurrences are not uncommon, and some tumors are even known to undergo malignant transformations

Who gets Benign Myoepithelioma? (Age and Sex Distribution)

• Myoepitheliomas can be present in individuals of a wide age range. However, a predilection for young and middle-aged adults is noted (median age 40 years)
• 1 in 5 Benign Myoepithelial Tumors are reported in children
• Both males and females are affected almost equally
• All races and ethnic groups may be affected

What are the Risk Factors for Benign Myoepithelioma? (Predisposing Factors)

• No clearly identified risk factors for Benign Myoepithelioma have been established to date

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Benign Myoepithelioma? (Etiology)

The cause of formation of Benign Myoepithelioma is due to genetic mutations and the following are noted:

• Mutation on EWSR1 gene is observed in extra-salivary gland myoepithelial tumors (in about half of the cases)
• Fusion of EWSR1 gene with either POU5F1 or PBX1 gene seen in over 15% of the myoepithelial tumors
• Infrequently, EWSR1-ZNF444 fused gene is known to display chromosomal translocation t(19;22)(q13;q12); this translocation is also linked to abnormalities in the FUS gene
• In young adults/older children - deep soft tissue tumors on limbs have reported a fusion of EWSR1 and POU5F1 genes
• Other chromosomal aberrations noted include t(1;22)(q23;q12), t(6;22)(p21;q12) and rearrangement of 16p11.2

Tumors without EWSR1 gene abnormality are observed to be located on the skin and are mostly benign; they also present ductal differentiation. These tumors are known as mixed myoepitheliomas. PLAG1 gene involvement in Benign Myoepithelioma showing ductal differentiation are also termed mixed tumors.

What are the Signs and Symptoms of Benign Myoepithelioma?

The signs and symptoms of Benign Myoepithelioma may include:

• Myoepitheliomas grow slowly and generally do not present any pain
• In many, the presence of a tumor mass that may be felt/touched is observed
• The tumors appear as fleshy or firm nodules that are well-defined
• Tumors may be small or large with size ranging from 10 mm to 20 cm; average size varies from 4-6 cm
• Rarely, some tumors may infiltrate into the surrounding tissues
• 75% of the myoepithelial tumors involve the arms and legs (legs more than arms), including the armpits (shoulder girdle) and groin (pelvic girdle)
• Infrequently, chest, back, abdomen, and head and neck region may be involved
• Tumors have, even rarely, been observed in the internal organs and bones
• A significant subset of the tumors is seen on the skin (superficial myoepithelioma)
• Tumors below the skin (subcutaneous myoepitheliomas) are more often noted, than tumors deep in the body affecting the organs/deep soft tissues

How is Benign Myoepithelioma Diagnosed?

The following exams and procedures may be used in the diagnosis of a Benign Myoepithelioma:

• Evaluation of the individual’s medical history and a through physical examination
• Imaging studies including plain X-ray and ultrasound scan of the affected region
• CT or CAT scan with contrast of the affected region may show a well-defined mass. This radiological procedure creates detailed 3-dimensional images of structures inside the scanned region
• MRI scans of head and neck region: A magnetic field is used to create high-quality pictures of certain parts of the body, such as tissues, muscles, nerves, and bones. These high-quality pictures may reveal the presence of the tumor

Although the above modalities can be used to make an initial diagnosis, a tissue biopsy of the tumor is necessary to make a definitive diagnosis to begin treatment. The tissue for diagnosis can be procured in multiple different ways which include: 

• Fine needle aspiration (FNA) biopsy of the tumor: A FNA biopsy may not be helpful, because one may not be able to visualize the different morphological areas of the tumor. Hence, a FNA biopsy as a diagnostic tool has certain limitations, and an open surgical biopsy may be recommended.
• Core biopsy of the tumor
• Open biopsy of the tumor

Tissue biopsy:

• A tissue biopsy of the tumor is performed and sent to a laboratory for a pathological examination. A pathologist examines the biopsy under a microscope. After putting together clinical findings, special studies on tissues (if needed) and with microscope findings, the pathologist arrives at a definitive diagnosis. Examination of the biopsy under a microscope by a pathologist is considered to be gold standard in arriving at a conclusive diagnosis
• Biopsy specimens are studied initially using Hematoxylin and Eosin staining. The pathologist then decides on additional studies depending on the clinical situation
• Sometimes, the pathologist may perform special studies, which may include immunohistochemical stains, molecular testing, and very rarely, electron microscopic studies to assist in the diagnosis

Note: 

• 1 in 10 tumors show additional glandular component (minor ductal component), when examined under a microscope by a pathologist. In such cases, the tumors are called mixed myoepitheliomas
• A differential diagnosis is often considered before arriving at a definitive diagnosis

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Benign Myoepithelioma?

The following complications due to Benign Myoepithelioma may be observed:

• Emotional stress and cosmetic concerns (if the tumors are superficially located, or are present in the head and neck region)
• Some tumors can be locally-infiltrative and destroy the surrounding tissue structures
• Deep-seated tumors may adversely affect the function of the organs
• The tumors are known to recur following surgery to remove them
• Occasionally, recurrent and/or longstanding tumors are known to transform into malignancy (malignant myoepithelioma)
• Surgical complications and post-surgical wound infections

How is Benign Myoepithelioma Treated?

• A complete surgical excision with clear or wide margins is the preferred mode of treatment of Benign Myoepithelioma
• Tumor recurrence may result in a need for multiple surgeries and/or more extensive therapies
• Radiation therapy may be administered when surgery is not a feasible treatment tool
• Post-operative care is important: One must maintain minimum activity levels, until the surgical wound heals
• Long-term follow-up may be required, because recurrence at the site of surgery have been reported many years after surgery

How can Benign Myoepithelioma be Prevented?

• Current medical research has not established a method of preventing the formation of Benign Myoepithelioma
• Regular medical screening at periodic intervals with blood tests, radiological scans, and physical examinations, for those who have already endured the tumor are helpful

What is the Prognosis of Benign Myoepithelioma? (Outcomes/Resolutions)

• The prognosis of Benign Myoepithelioma is generally excellent with surgical intervention and complete removal, since it is a benign tumor. However, about 1 in 5 tumors are known to recur
• Besides recurrence, malignant transformations and metastasis have been noted in rare cases. In such cases, the prognosis may depend upon the stage of the tumor, among other factors

Additional and Relevant Useful Information for Benign Myoepithelioma:

• Myoepithelioma of salivary gland is an uncommon benign tumor typically arising in the major salivary glands. It can be present in individuals of a wide age range (including children and adults)

The following DoveMed website link is a useful resource for additional information:

http://www.dovemed.com/diseases-conditions/myoepithelioma-salivary-gland/