This article was last reviewed and updated on April 30, 2019

by Jason Wasserman, MD PhD FRCPC

Quick facts:

• Pleomorphic adenoma is the most common type of salivary gland tumour.

• Most start in a large salivary gland called the parotid gland.

• Most pleomorphic adenomas are non-cancerous although a small number can spread to other parts of the body or turn into a cancer over time.

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Normal salivary glands

When we chew food our body releases a fluid into the mouth called saliva. Saliva is important because it contains chemicals that aid in digestion. Saliva is produced by organs called salivary glands which are located throughout the head and neck.

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Most people have three major salivary glands and numerous minor salivary glands. The major salivary glands are called the parotid gland, submandibular gland, and sublingual gland. The minor salivary glands are very small and there are so many of them that they are not given their own names. Most of the minor salivary glands are found inside the mouth.

 

The parotid gland is the largest salivary gland and it can be found on the side of the face just in front of the ear. The submandibular gland can be found just below the lower jaw near the top of the neck. The sublingual gland is the smallest of the major glands and it can be found below the tongue.

 

The salivary glands are made up of small groups of cells called glands which are connected to the inside of the mouth by long thin channels called ducts. The glands make the chemicals in the saliva which travels down the ducts into the mouth.

 

What is a pleomorphic adenoma?

Pleomorphic adenoma is the most common type of salivary gland tumour. Pleomorphic adenomas can arise in a variety of body sites including the skin and lungs although the vast majority arise in the parotid gland. Pleomorphic adenomas are slow growing tumours although they can reach a large size without treatment.
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Most pleomorphic adenomas behave like non-cancerous (benign) tumours, however, they can grow back again in the same location if not completely removed. Most pleomorphic adenomas are made up of a combination of glands and ducts in various shapes and sizes.

 

Rarely, a cancer (a malignant tumour) will develop from within a pleomorphic adenoma. These tumours are called carcinoma ex-pleomorphic adenoma which is just the medical way of saying 'cancer arising from a pleomorphic adenoma'.  Tumours that are very large, have been present for many years, or have come back multiple times have a higher risk of developing cancer.

 

Because pleomorphic adenoma can turn into a cancer over time, it is recommended that all pleomorphic adenomas are removed completely.

The first diagnosis of pleomorphic adenoma is usually made after a small piece of tissue is removed from the tumour in a procedure called a biopsy. The tumour is later removed completely in a a surgical procedure called a resection.

Tumour size

This is the size of the tumour measured in centimeters (cm). Tumour size will only be described in your report after the entire tumour has been removed. The tumour is usually measured in three dimensions but only the largest dimension is described in your report. For example, if the tumour measures 4.0 cm by 2.0 cm by 1.5 cm, your report will describe the tumour as being 4.0 cm.

Margins
A margin is a small amount of normal tissue that surrounds a tumour and is removed with the tumour at the time of surgery.

 

Some pathology reports will include information about tumour cells at the cut edge of the margin. If tumour cells are seen at the very edge of the tissue, the margin is called positive. If no tumour cells are seen at the edge of the tissue, the margin is called negative.

Margins will only be described in your report after the entire tumour has been removed,

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Why is this important? A positive margin is associated with an increased risk that the tumour will grow back after treatment.

Lymph nodes​
Lymph nodes are small organs, located in various locations throughout the body. They form part of the body's immune surveillance system. When tumour cells travel to a lymph node it is called a lymph node metastasis.

It is common for lymph nodes around the tumour to be removed at the same time as the tumour. Your pathologist will examine each of these lymph nodes under the microscope to see if any contain tumour cells.

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Why is this important? Tumour cells from a pleomorphic adenoma rarely travel to a lymph node. If tumour cells are found in a lymph node, your pathologist will examine them to see if they have changed to look more like cancer cells or if they still look similar to the cells in the pleomorphic adenoma.

Immunohistochemistry
Pleomorphic adenoma are commonly composed of three cell types and pathologists occasionally perform a test called immunohistochemistry on these tumours which helps your pathologist clearly see all three cell types.

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