This article will help you read and understand your pathology report for salivary duct carcinoma.
by Jason Wasserman, MD PhD FRCPC (June 20, 2021)
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 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 affected. 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.
Salivary duct carcinoma ex pleomorphic adenoma is a term pathologists use to describe a salivary duct carcinoma that starts from within a previously benign (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.
Salivary duct carcinoma is made up of large pink cells. Pathologists describe these cells as eosinophilic. 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.
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.
After the tumour has been removed completely, it will be sent to a pathologist who will prepare another pathology report. This report will confirm or revise the original diagnosis and provide additional important information such tumour size, extraparenchymal extension, margin status, and spread of tumour cells to lymph nodes. This information is used to determine the cancer stage and to decide if additional treatment is required.
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.
Parenchyma is a word used to describe the normal tissue of an organ. Because mucoepidermoid carcinoma typically starts in a salivary gland, parenchyma is used to describe the normal salivary gland tissue.
Extraparenchymal extension means that the cancer cells have grown beyond the normal salivary gland tissue and are seen in the surrounding tissue.
Tumours that have grown beyond the normal salivary gland tissue 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).
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.
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.
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.
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.
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).
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).
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 the distance that the cancer cells have traveled 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.