by Jason Wasserman MD PhD FRCPC
May 4, 2023
Salivary duct carcinoma is a type of salivary gland cancer. 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 most common location for salivary duct carcinoma is the parotid gland, however, the tumour can also arise in the submandibular or sublingual gland.
The symptoms of salivary duct carcinoma typically include a rapidly growing mass in the cheek or neck with pain or weakness in the face.
The cause of salivary duct carcinoma is currently unknown.
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.
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 described as atypical because they are very abnormal-looking compared to normal, healthy cells. Dividing tumour cells called mitotic figures are commonly seen. 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.
When immunohistochemistry (IHC) is performed the tumour cells in salivary duct carcinoma are typically positive for androgen receptor (AR), pan-cytokeratin, GATA-3, and mammaglobin. The tumour cells are typically negative for S100 and cytokeratin 20.
After the tumour has been removed completely it will be measured and the size will be described in your report. The tumour size is important because it is used to determine the pathologic tumour stage (pT).
The term extraparenchymal extension describes a tumour that has grown beyond the normal salivary gland and into surrounding organs or tissue. Extraparenchymal extension is important because 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 pathologic tumour stage (pT).
Nerves are like long wires made up of groups of cells called neurons. Nerves are found all over the body and they are responsible for sending information (such as temperature, pressure, and pain) between your body and your brain. Perineural invasion is a term pathologists use to describe tumour cells attached to a nerve. Perineural invasion is important because the tumour cells can use the nerve to spread into surrounding tissues. This increases the risk that the tumour will re-grow after treatment.
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 specialized vessels called lymphatics. The term lymphovascular invasion is used to describe tumour cells that are found inside a blood or lymphatic vessel. Lymphovascular invasion is important because these cells are able to metastasize (spread) to other parts of the body such as lymph nodes or the lungs.
A margin is any tissue that was cut by the surgeon in order to remove the tumour from your body. Whenever possible, surgeons will try to cut tissue outside of the tumour to reduce the risk that any cancer cells will be left behind after the tumour is removed. Most reports will only describe margins after the entire tumour has been removed.
Your pathologist will carefully examine all the margins in your tissue sample to see how close the cancer cells are to the edge of the cut tissue. A negative margin means there were no cancer cells at the very edge of the cut tissue. If all the margins are negative, most pathology reports will usually say how far the closest cancer cells were to a margin. The distance is usually described in millimetres. A positive margin means there were cancer cells at the very edge of the cut tissue. A positive margin is associated with a higher risk that the tumour will grow back in the same site after treatment (local recurrence).
Lymph nodes are small immune organs located throughout the body. Tumour 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 tumour 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 tumour cells. Lymph nodes that contain tumour cells are often called positive while those that do not contain any tumour cells are called negative. Most reports include the total number of lymph nodes examined and the number, if any, that contain tumour cells.
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.
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).
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:
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.