Mucosal melanoma of the head and neck

by Jason Wasserman MD PhD FRCPC
August 4, 2022


What is mucosal melanoma?

Mucosal melanoma is a type of cancer that starts from a thin layer of tissue called mucosa. In the head and neck, mucosa is found inside the mouth (oral cavity), nose (nasal cavity), paranasal sinuses (maxillary sinus, ethmoid sinus, frontal sinus, and sphenoid sinus), and throat (pharynx and larynx). The tumour is made up of abnormal melanocytes.

What are the symptoms of mucosal melanoma?

The symptoms of mucosal melanoma vary depending on the area of the head and neck involved. Tumours that start in the nose (nasal cavity) or one of the paranasal sinuses can cause symptoms such as nasal congestion, runny nose, or frequent nose bleeds. Tumours that start in the mouth (oral cavity) frequently do not cause any symptoms although some patients may experience pain later in the disease. Tumours that start in the throat can cause voice changes such as hoarseness or difficulty breathing.

What causes mucosal melanoma?

Doctors do not know what causes most mucosal melanomas. However, people with a non-cancerous condition called mucosal melanosis appear to be at a higher risk of developing this type of cancer at some point in their lives. Unlike melanoma in the skin, mucosal melanoma in the head and neck is not caused by excessive exposure to UV light (such as the sun).

How common is mucosal melanoma?

Mucosal melanoma in the head and neck is a very rare disease that accounts for approximately 1% of all cases of melanoma. Most melanomas start in the skin.

How is the diagnosis of mucosal melanoma made?

The diagnosis is usually made after a small sample is the tumour is removed in a procedure called a biopsy. The tissue is then sent to a pathologist who examines it under the microscope. A second surgical procedure is then usually performed to remove the entire tumour.

What does mucosal melanoma look like under the microscope?

Mucosal melanoma is made up of abnormal melanocytes. Melanocytes are a specialized type of cell that can be found throughout the body. Melanocytes make a brown pigment called melanin and this pigment may be seen in the tumour. The cancer cells in the tumour may be described as epithelioid (round), spindled (long and thin), rhabdoid (similar to muscle cells), plasmacytoid (similar to immune cells called plasma cells), or clear (the cytoplasm, or body of the cell, looks clear). A type of cell death called necrosis and mitotic figures (cancer cells dividing to create new cancer cells) are also typically seen.

Mucosal melanoma of the head and neck
Mucosal melanoma of the head and neck. This picture shows a tumour in the oral cavity.

What other tests may be performed to confirm the diagnosis of mucosal melanoma?

Your pathologist may perform a test called immunohistochemistry to confirm the diagnosis. This test allows your pathologist to see specialized chemicals called proteins inside the cancer cells. The cancer cells in the tumour make the same proteins found in normal melanocytes. These proteins include S100, SOX-10, Melan-A, and HMB-45.

What is lymphovascular invasion and why is it important?

Lymphovascular invasion means that cancer cells were seen inside of a blood vessel or lymphatic vessel. Blood vessels are long thin tubes that carry blood around the body. Lymphatic vessels are similar to small blood vessels except that they carry a fluid called lymph instead of blood. The lymphatic vessels connect with small immune organs called lymph nodes that are found throughout the body. Lymphovascular invasion is important because cancer cells can use blood vessels or lymphatic vessels to spread to other parts of the body such as lymph nodes or the lungs.

Lymphovascular invasion
Lymphovascular invasion

What is perineural invasion and why is it important?

Perineural invasion is a term pathologists use to describe cancer cells attached to or inside a nerve. A similar term, intraneural invasion, is used to describe cancer cells inside a nerve. 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 important because the cancer cells can use the nerve to spread into surrounding organs and tissues. This increases the risk that the tumour will regrow after surgery.

Perineural invasion
Perineural invasion

Were lymph nodes examined and did any contain cancer cells?

Lymph nodes are small immune organs found throughout the body. Cancer cells can spread from a tumour to lymph nodes through small vessels called lymphatics. For this reason, lymph nodes are commonly removed and examined under a microscope to look for cancer cells. The movement of cancer cells from the tumour to another part of the body such as a lymph node is called a metastasis.

Cancer cells typically spread first to lymph nodes close to the tumour although lymph nodes far away from the tumour can also be involved. For this reason, the first lymph nodes removed are usually close to the tumour. Lymph nodes further away from the tumour are only typically removed if they are enlarged and there a high clinical suspicion that there may be cancer cells in the lymph node.

If any lymph nodes were removed from your body, they will be examined under the microscope by a pathologist and the results of this examination will be described in your report. Most reports will include the total number of lymph nodes examined, where in the body the lymph nodes were found, and the number (if any) that contain cancer cells. If cancer cells were seen in a lymph node, the size of the largest group of cancer cells (often described as “focus” or “deposit”) will also be included.

The examination of lymph nodes is important for two reasons. First, this information is used to determine the pathologic nodal stage (pN). Second, finding cancer cells in a lymph node increases the risk that cancer cells will be found in other parts of the body in the future. As a result, your doctor will use this information when deciding if additional treatment such as chemotherapy, radiation therapy, or immunotherapy is required.

Lymph node

What does it mean if a lymph node is described as positive?

Pathologists often use the term “positive” to describe a lymph node that contains cancer cells. For example, a lymph node that contains cancer cells may be called “positive for malignancy” or “positive for metastatic carcinoma”.

What does it mean if a lymph node is described as negative?

Pathologists often use the term “negative” to describe a lymph node that does not contain any cancer cells. For example, a lymph node that does not contain cancer cells may be called “negative for malignancy” or “negative for metastatic carcinoma”.

What does extranodal extension mean?

All lymph nodes are surrounded by a thin layer of tissue called a capsule. Extranodal extension means that cancer cells within the lymph node have broken through the capsule and have spread into the tissue outside of the lymph node. Extranodal extension is important because it increases the risk that the tumour will regrow in the same location after surgery. For some types of cancer, extranodal extension is also a reason to consider additional treatment such as chemotherapy or radiation therapy.

extranodal extension

What is a margin?

In pathology, a margin is the edge of a tissue that is cut when removing a tumour from the body. The margins described in a pathology report are very important because they tell you if the entire tumour was removed or if some of the tumour was left behind. The margin status will determine what (if any) additional treatment you may require.

Most pathology reports only describe margins after a surgical procedure called an excision or resection has been performed for the purpose of removing the entire tumour. For this reason, margins are not usually described after a procedure called a biopsy is performed for the purpose of removing only part of the tumour. The number of margins described in a pathology report depends on the types of tissues removed and the location of the tumour. The size of the margin (the amount of normal tissue between the tumour and the cut edge) depends on the type of tumour being removed and the location of the tumour.

Pathologists carefully examine the margins to look for tumour cells at the cut edge of the tissue. If tumour cells are seen at the cut edge of the tissue, the margin will be described as positive. If no tumour cells are seen at the cut edge of the tissue, a margin will be described as negative. Even if all of the margins are negative, some pathology reports will also provide a measurement of the closest tumour cells to the cut edge of the tissue.

A positive (or very close) margin is important because it means that tumour cells may have been left behind in your body when the tumour was surgically removed. For this reason, patients who have a positive margin may be offered another surgery to remove the rest of the tumour or radiation therapy to the area of the body with the positive margin. The decision to offer additional treatment and the type of treatment options offered will depend on a variety of factors including the type of tumour removed and the area of the body involved. For example, additional treatment may not be necessary for a benign (non-cancerous) type of tumour but may be strongly advised for a malignant (cancerous) type of tumour.

Margin

How is mucosal melanoma staged?

Your pathologist can only determine the tumour stage after the entire tumour has been removed. By definition, all mucosal melanomas of the head and neck are given a tumour stage (pT) of pT3 or pT4. A tumour is considered pT3 when it only involves the mucosa in one area of the head and neck. A tumour that grows into surrounding tissues including bones, large nerves, blood vessels, or the skin is considered pT4. The nodal stage (pN) is based on the examination of lymph nodes to look for cancer cells. If no cancer cells are found in any of the lymph nodes examined, the nodal stage is pN0. If cancer cells are found in any of the lymph nodes examined, the nodal stage is pN1. In cases where no lymph nodes were sent for examination by the pathologist, the nodal stage cannot be determined as is called pNx. Higher-stage tumours (those that are pT4 or pN1) are associated with a worse prognosis.

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