Myoepithelioma of the salivary glands

by Jason Wasserman MD PhD FRCPC
November 29, 2024

A myoepithelioma is a non-cancerous type of salivary gland tumour. It is made up of specialized myoepithelial cells that are normally found in the salivary gland. This tumour should not be confused with the similarly named myoepithelioma that starts in soft tissue.

Is myoepithelioma a type of cancer?

No. Myoepithelioma is a benign (non-cancerous) type of tumour.

What causes a myoepithelioma?

At present, doctors do not know what causes myoepithelioma.

What are the symptoms of myoepithelioma?

The symptoms of myoepithelioma are typically a slow-growing, painless mass.

How is this diagnosis made?

The diagnosis of myoepithelioma can be made after tissue from the tumour is examined under the microscope by a pathologist.

Microscopic features of this tumour

When examined under the microscope, myoepithelioma is well-circumscribed (there is a clear border around the entire tumour), surrounded by a thin tumour capsule, and made up entirely of myoepithelial cells. The tumour cells may look spindled (long and thin), epithelioid (round and connected), or plasmacytoid (similar to plasma cells). The stroma (connective tissue) surrounding the tumour cells may be described as myxoid, chondromyxoid, or fibrotic. The tumour cells usually show very little cytologic atypia and mitotic figures (cells dividing to create new cells) are rarely seen.

Immunohistochemistry

Immunohistochemistry is a special laboratory test that pathologists use to identify specific proteins in tumour cells. This test involves applying antibodies that bind to these proteins on a tissue sample, which is then examined under a microscope. By identifying the proteins present, pathologists can confirm the diagnosis and better understand the tumour’s characteristics.

In myoepithelioma of the salivary glands, the tumour cells typically show positive staining for proteins such as S100, cytokeratins (like CK AE1/AE3), and smooth muscle actin (SMA). These results reflect the myoepithelial origin of the tumour. Other markers, such as GFAP, may also be positive, particularly in tumours with a significant myxoid (gel-like) component. These findings help distinguish myoepithelioma from other salivary gland tumours with similar appearances.