Adenoid cystic carcinoma (ACC) is a type of cancer. Most start in one of the salivary glands. However, it can also start in other parts of the body, such as the skin or the breast.
Most adenoid cystic carcinomas are small tumours (typically less than 5 cm) that grow slowly over time. However, groups of tumour cells commonly surround nerves and use the nerves to spread into the surrounding tissues. This is called perineural invasion. Because of this, the tumour is often difficult to remove completely by surgery alone. Unfortunately, the overall prognosis is poor as many patients experience late local recurrences and distant metastasis.
Depending on the location of the tumour, the symptoms of an adenoid cystic carcinoma may include an ulcer in the roof of the mouth, a slow-growing lump in the face or neck, pain, or inability to move some of the muscles on one side of the face. The last two symptoms suggest that the tumour cells have surrounded a large nerve in the face called the facial nerve (cranial nerve VII).
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.
Most adenoid cystic carcinomas are first diagnosed after a small tissue sample is removed in a procedure called a biopsy. A similar procedure called a fine needle aspiration biopsy may also be performed.
Adenoid cystic carcinomas are commonly composed of two main cell types: ductal and myoepithelial cells. Your pathologist may perform a test called immunohistochemistry on the tissue sample. This test allows the pathologist to see both the ductal and myoepithelial cells in the tumour.
When immunohistochemistry is performed, adenoid cystic carcinoma can show the following results:
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 as tumour size, margins, 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.
Grade is a word pathologists use to describe the difference between the cancer cells and the cells normally found in the salivary glands. Higher grade tumours are more abnormal and look less like normal tissue.
Adenoid cystic carcinoma is graded on a scale of 1 to 3 (or low, intermediate, and high) based on the amount of tumour cells that are growing in very large groups. Pathologists describe this as a solid pattern of growth.
Higher grade tumours (grades 2 and 3) are more aggressive tumours that are more likely to re-grow after surgery.
This is the size of the tumour measured in centimetres after it has been removed fully from your body. Your pathologist will measure it in three dimensions although only the largest dimension is typically included in your report. For example, if the tumour measures 5.0 cm by 3.2 cm by 1.1 cm, the report may describe the tumour size as 5.0 cm in the greatest dimension.
The tumour size is important because it is used to determine the tumour stage (see Pathologic stage below). Larger tumours are associated with a worse prognosis and are more likely to re-grow or spread to other parts of the body.
Parenchyma is a word used to describe the normal tissue of an organ. Because adenoid cystic 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.
Extraparenchymal extension is used to determine the tumour stage (see Pathologic stage below). Tumours that have grown beyond the normal salivary gland tissue are also more likely to spread to other parts of the body such as lymph nodes.
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. Margins will only be described in your report 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).
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.
Perineural invasion is important because cancer cells that have attached to a nerve can use the nerve to travel into tissue outside of the original tumour. Perineural invasion is also associated with a higher risk that the tumour will come back in the same area of the body (local recurrence) after treatment. Perineural invasion is almost always seen in an adenoid cystic carcinoma. If perineural invasion is not seen after the entire tumour has been removed, the diagnosis should be questioned.
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.
The tumour cells in an adenoid cystic carcinoma almost never invade lymphatics. However, late in the course of the disease, tumour cells in an adenoid cystic carcinoma may be seen invading blood vessels.
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.
Most reports include the total number of lymph nodes examined and the number, if any, that contain cancer cells. 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 all lymph nodes 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.
Finding cancer cells in a lymph node is important because it is associated with a higher risk that the cancer cells will be found in other lymph nodes or in a distant organ such as the lungs. However, unlike other types of cancer, the cancer cells in an adenoid cystic carcinoma are very rarely found in a lymph node.
The pathologic stage for adenoid cystic 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.
Adenoid cystic 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 travelled outside of the salivary gland (extraparenchymal extension).
Adenoid cystic 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:
Adenoid cystic carcinoma is given a metastatic stage between 0 and 1 based on the presence 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 sent for pathological examination. Because this tissue is rarely sent, the metastatic stage cannot be determined and is listed as MX.