Pleomorphic adenoma

by Jason Wasserman MD PhD FRCPC
June 27, 2022

What is a pleomorphic adenoma?

Pleomorphic adenoma (PA) is a non-cancerous salivary gland tumour and the most common type of salivary gland tumour in adults. Pleomorphic adenomas are slow-growing tumours although they can reach a large size without treatment. Another name for this type of tumour is benign mixed tumour.

Where in the body are pleomorphic adenomas found?

Most pleomorphic adenomas are found in one of the salivary glands such as the parotid or submandibular gland. Pleomorphic adenomas can also start in one of the minor salivary glands located throughout the mouth. Although rare, pleomorphic adenomas can also be found in the skin, nasal cavity, large airways, and lungs.

Can pleomorphic adenoma turn into cancer?

Pleomorphic adenoma is a non-cancerous tumour, however, it can over time change into a type of cancer. Doctors call this change “carcinoma ex pleomorphic adenoma”. Large tumours and those that have been present for many years are associated with an increased risk of cancer. For these reasons, all pleomorphic adenomas should be completely removed.

What causes pleomorphic adenoma?

At this time doctors do not know what causes pleomorphic adenoma.

What genetic changes are found in pleomorphic adenoma?

Most pleomorphic adenomas harbour a genetic change involving the genes PLAG1 (approximately 50%) or HMGA2 (approximately 15%). The changes involved are called fusions because they result in one of these changes becoming attached to another gene.

Your pathology report for pleomorphic adenoma

The information found in your pathology report for pleomorphic adenoma will depend on the type of procedure performed. A biopsy is a surgical procedure that removes a small piece of tissue from the tumour. The tissue is then sent to a pathologist for examination under a microscope.  The purpose of a biopsy is to provide a diagnosis. Additional information such as the tumour size and margins examined are not usually included until a procedure is performed to remove the entire tumour.

pleomorphic adenoma
This picture shows a pleomorphic adenoma viewed at low power through a microscope.
What is a margin and why are margins important?

A margin is any tissue that was cut by the surgeon in order to remove the tumour from your body. The types of margins described in your report will depend on the area of the body involved and the type of surgery performed. Margins are usually only described after the entire tumour has been surgically removed.

A negative margin means that no tumour cells were seen at any of the cut edges of the tissue. A margin is called positive when there are tumour cells at the very edge of the cut tissue. A positive margin is associated with an increased risk that the tumour will re-grow in the same location in the future.


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