Salivary duct carcinoma

What is salivary duct carcinoma?

Salivary duct carcinoma is a type of salivary gland cancer. The most common location for salivary duct carcinoma is the parotid gland, however, any of the major or minor salivary glands can be involved. Salivary duct carcinoma is an aggressive cancer that often spreads into the tissue surrounding the salivary gland and to other organs such as lymph nodes and the lungs.

The salivary glands

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

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.

Salivary duct carcinoma ex pleomorphic adenoma

Salivary duct carcinoma ex pleomorphic adenoma is a term pathologists use to describe a salivary duct carcinoma that starts from within a previously non-cancerous tumour called pleomorphic adenoma.

How do pathologists make this diagnosis?

The diagnosis of salivary duct carcinoma is usually made after a small sample of the tumour is removed in a procedure called a biopsy. The diagnosis can also be made after the entire tumour is removed in a larger surgical procedure called a resection. The tissue is then sent to a pathologist for examination.

When examined under the microscope, salivary duct carcinoma is made up of large pink cells. Pathologists describe these cells as eosinophilic. The tumour cells in salivary duct carcinoma are very abnormal-looking compared to normal, healthy cells. Pathologists describe these cells as atypical. Dividing tumour cells called mitotic figures are commonly see. The tumour cells often connect together to form small finger-like projections called papillae or micropapillae. Small open spaces called cysts may also be seen in the tumour.

salivary duct carcinoma

Your pathologist may perform a test called immunohistochemistry to confirm the diagnosis. The tumour cells in salivary duct carcinoma are typically positive or reactive for androgen receptor (AR), pan-cytokeratin, GATA-3, and mammaglobin. The tumour cells are typically negative or non-reactive for S100 and cytokeratin-20.

What to look for in your report after the tumour has been removed

Tumour size

This is the size of the tumour measured in centimetres (cm). 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.

Extraparenchymal extension

Parenchyma is a word used to describe the normal tissue on the inside of an organ. Because salivary duct carcinoma typically starts in a salivary gland, parenchyma is used to describe the normal salivary gland tissue.

Pathologists use the term extraparenchymal extension to describe a tumour that has grown beyond the normal salivary gland tissue and into the surrounding tissue. Tumours that show extraparenchymal extension are more likely to spread to other parts of the body such as lymph nodes. Extraparenchymal extension is also used to determine the tumour stage (see Pathologic stage below).

Margins

A margin is a rim of normal tissue that surrounds a tumour and is removed with the tumour at the time of surgery. The margins will usually only be described in your report after the entire tumour has been removed.

A negative margin means that no cancer cells were seen at the cut edge of the tissue. In contrast, a positive margin means that cancer cells were seen at the cut edge of the tissue. A positive margin is associated with an increased risk that the tumour will grow back in the same location after treatment.

Margin

Lymphovascular invasion

Blood moves around the body through long thin tubes called blood vessels. Another type of fluid called lymph which contains waste and immune cells moves around the body through lymphatic channels.

Cancer cells can use blood vessels and lymphatics to travel away from the tumour to other parts of the body. The movement of cancer cells from the tumour to another part of the body is called metastasis.

Before cancer cells can metastasize, they need to enter a blood vessel or lymphatic. This is called lymphovascular invasion. Lymphovascular invasion increases the risk that cancer cells will be found in a lymph node or a distant part of the body such as the lungs.

lymphovascular invasion

Perineural invasion

Nerves are like long wires made up of groups of cells called neurons. Nerves send information (such as temperature, pressure, and pain) between your brain and your body. Perineural invasion means that cancer cells were seen attached to a nerve.

Cancer cells that have attached to a nerve can use the nerve to travel into tissue outside of the original tumour. This increases the risk that the tumour will come back in the same area of the body (recurrence) after treatment.

perineural invasion

Lymph nodes

Lymph nodes are small immune organs located throughout the body. Cancer cells can travel from the tumour to a lymph node through lymphatic channels located in and around the tumour (see Lymphovascular invasion above). The movement of cancer cells from the tumour to a lymph node is called metastasis.

Lymph nodes from the neck are sometimes removed at the same time as the main tumour in a procedure called a neck dissection. The lymph nodes removed usually come from different areas of the neck and each area is called a level. The levels in the neck include 1, 2, 3, 4, and 5. Your pathology report will often describe how many lymph nodes were seen in each level sent for examination.

Lymph nodes on the same side as the tumour are called ipsilateral while those on the opposite side of the tumour are called contralateral.

Your pathologist will carefully examine each lymph node for cancer cells. Lymph nodes that contain cancer cells are often called positive while those that do not contain any cancer cells are called negative. Most reports include the total number of lymph nodes examined and the number, if any, that contain cancer cells.

Lymph node

Tumour deposit

A group of cancer cells inside of a lymph node is called a tumour deposit. If a tumour deposit is found, your pathologist will measure the deposit and the largest tumour deposit found will be described in your report. Larger tumour deposits are associated with a worse prognosis. The size of the largest tumour deposit is also used to determine the nodal stage (see Pathologic stage below).

Extranodal extension (ENE)

All lymph nodes are surrounded by a capsule. Extranodal extension (ENE) means that cancer cells have broken through the capsule and into the tissue that surrounds the lymph node. Extranodal extension is also associated with a higher risk of new tumours developing in the neck and is often used by your doctors to guide your treatment. Extranodal extension is also used to determine the nodal stage (see Pathologic stage below).

Pathologic stage

​The pathologic stage for salivary duct carcinoma is based on the TNM staging system, an internationally recognized system originally created by the American Joint Committee on Cancer. This system uses information about the primary tumour (T), lymph nodes (N), and distant metastatic disease (M)  to determine the complete pathologic stage (pTNM). Your pathologist will examine the tissue submitted and give each part a number. In general, a higher number means more advanced disease and a worse prognosis.

Tumour stage (pT) for salivary duct carcinoma

Salivary duct carcinoma is given a tumour stage from 1 to 4 based on the size of the tumour and whether the cancer cells have spread outside of the salivary gland (extraparenchymal extension).

  • T1 – The tumour is less than 2 cm in size and is still found entirely within the salivary gland.
  • T2 – The tumour is between 2 cm and 4 cm in size and is still found entirely within the salivary gland.
  • T3 – The tumour is larger than 4 cm in size AND/OR extraparenchymal extension is seen.
  • T4 – The cancer cells have spread to any of the organs that normally surround the salivary gland. These organs include large blood vessels, bones, skin, or the ear.
Nodal stage (pN) for salivary duct carcinoma

Salivary duct carcinoma is given a nodal stage from 0 to 3. If no cancer cells are seen in any of the lymph nodes examined, the nodal stage is N0. If cancer cells are seen in a lymph node, your pathologist will look for the following features to determine the nodal stage:

  • Size  – The group of cancer cells in the lymph node will be measured. A size greater than 3 cm or 6 cm increases the nodal stage.
  • Extranodal extension – All lymph nodes are surrounded by a thin layer of tissue called a capsule. If cancer cells break through the capsule and enter the tissue surrounding the lymph node it is called extranodal extension. Extranodal extension increases the nodal stage.
  • Number of lymph nodes with cancer cells – Your pathologist will count the number of lymph nodes that contain cancer cells. Cancer cells found in more than one lymph node increases the nodal stage.
  • Location of lymph nodes – Cancer cells found in a lymph node on the same side of the tumour are called ipsilateral. Cancer cells found in a lymph node on the opposite side of the tumour are called contralateral. Cancer cells found in a contralateral lymph node increases the nodal stage.​
Metastatic stage (pM) for salivary duct carcinoma

Salivary duct carcinoma is given a metastatic stage of 0 or 1 based on the finding of cancer cells at a distant site in the body (for example the lungs). The metastatic stage can only be determined if tissue from a distant site is submitted for pathological examination. Because this tissue is rarely present, the metastatic stage cannot be determined and is listed as MX.

by Jason Wasserman, MD PhD FRCPC (updated August 22, 2021)
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