Sinonasal undifferentiated carcinoma (SNUC)

by Jason Wasserman MD PhD FRCPC
June 5, 2022


What is sinonasal undifferentiated carcinoma?

Sinonasal undifferentiated carcinoma (SNUC) is a type of cancer that starts from cells normally found on the inside of the nasal cavity and paranasal sinuses. This area of the body is called the sinonasal tract. Sinonasal undifferentiated carcinoma is an aggressive disease with a poor prognosis. The tumour cells in sinonasal undifferentiated carcinoma commonly spread outside of the sinonasal tract into the bones of the jaw, the orbit, and the base of the skull. The tumour cells also commonly travel to lymph nodes and other more distant parts of the body.

What causes sinonasal undifferentiated carcinoma?

Compared to other cancers of the head and neck, very little is known about what causes sinonasal undifferentiated carcinoma although some patients may have received radiation therapy in the past for a different cancer in the same area of the body.

How is the diagnosis of sinonasal undifferentiated carcinoma made?

The diagnosis of sinonasal undifferentiated carcinoma is usually made after a small sample of tissue is removed from your body in a procedure called a biopsy. The tissue is then sent to a pathologist who examines it under a microscope.

Most patients with sinonasal undifferentiated carcinoma will be treated with radiation although you may be offered surgery first to remove the tumour. If the tumour is removed, 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 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.

What does sinonasal undifferentiated carcinoma look like under the microscope?

When examined under the microscope, the cells in sinonasal undifferentiated carcinoma do not look like any of the cells normally found in the epithelium. Pathologists use the word undifferentiated to describe cancer cells that do not look anything like normal, healthy cells.

sinonasal undifferentiated carcinoma

Immunohistochemistry

Your pathologist may perform a test called immunohistochemistry on tissue from the tumour before they make the diagnosis of sinonasal undifferentiated carcinoma. The tumour cells in sinonasal undifferentiated carcinoma are usually positive (reactive) for proteins called keratins including pan-cytokeratin, low molecular weight keratin, and cytokeratin 8/18 (CK8/18).

The tumour cells are usually negative (non-reactive) for cytokeratin 5 (CK5), p40, synaptophysin, and chromogranin although any of these may be described as focally positive. Your report may also describe the cancer cells as being negative for p16, EBER, S100, and CD45.

Perineural invasion

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.

perineural invasion

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 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.

lymphovascular invasion

Margins

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.

The types of margins described in your report will depend on the parts of the sinonasal tract involved and the type of surgery performed. Margins are usually only described in your report after the entire tumour has been removed.

A negative margin means that no tumour cells were seen at any of the cut edges of tissue. A margin is called positive when there are tumour cells at the very edge of the cut tissue. A positive margin is associated with a higher risk that the tumour will recur in the same site after treatment.

Because sinonasal undifferentiated carcinoma is often removed in multiple pieces, your pathologist may not be able to reliably assess the margins of the tumour. For that reason, most pathology reports for sinonasal undifferentiated carcinoma do not have information about margins.

Margin

Lymph nodes

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.

 

Lymph node

Tumour deposit

A group of tumour 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).

Pathologic stage (pTNM) for sinonasal undifferentiated carcinoma

​The pathologic stage for sinonasal undifferentiated 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 (pT), lymph nodes (pN), and distant metastatic disease (pM)  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 tumours that start in the nasal cavity or ethmoid sinus

These tumours are given a tumour stage between 1 and 4. The tumour stage is based on how far the tumour has spread outside of the nasal cavity or ethmoid sinus.

  • T1 – The tumour is limited to the nasal cavity or ethmoid sinus. It has not extended into the surrounding bones.
  • T2 – The tumour has spread out of the nasal cavity or ethmoid sinus.
  • T3 – The tumour has spread into the wall or floor of the orbit (the cavity that holds the eye), maxillary sinus, palate (the roof of the mouth), or cribriform plate (an area at the top of the nasal cavity).
  • T4 – The tumour has spread to the eye, skin of the nose or cheek, cranial cavity (the space that holds the brain), pterygoid plates (bones at the bottom of the cranial cavity), sphenoid or frontal sinuses.
Tumour stage (pT) for tumours that start in the maxillary sinus

These tumours are given a tumour stage between 1 and 4. The tumour stage is based on how far the tumour has spread outside of the maxillary sinus.

  • T1 – The tumour is limited to the maxillary sinus. It has not extended into the surrounding bones.
  • T2 – The tumour has spread out of the nasal cavity or ethmoid sinus.
  • T3 – The tumour has spread into the bone at the back of the maxillary sinus, subcutaneous tissues, floor or wall of the orbit (the cavity that holds the eye), pterygoid fossa, or ethmoid sinuses.
  • T4 – The tumour has spread to the eye, skin of the nose or cheek, cranial cavity (the space that holds the brain), pterygoid plates (bones at the bottom of the cranial cavity), sphenoid or frontal sinuses.
Nodal stage (pN) for tumours that start in the nasal cavity or paranasal sinuses

These tumours are given a nodal stage between 0 and 3 based on the following three features:

  1. The number of lymph nodes that contain cancer cells.
  2. The size of the tumour deposit.
  3. Whether the lymph nodes with cancer cells are on the same side (ipsilateral) or the opposite side (contralateral) of the tumour.

The nodal stage will be higher if any of the tumour deposits are larger than 3 cm, more than one lymph node contains cancer cells, cancer cells are found in lymph nodes on both sides of the neck, and if any of the lymph nodes show extranodal extension.

If no cancer cells are found in any of the lymph nodes examined, the nodal stage is N0.

If no lymph nodes are submitted for pathological examination, the nodal cannot be determined and the stage is listed as NX.

Metastatic stage (pM) for sinonasal undifferentiated carcinoma

Sinonasal undifferentiated carcinoma is given a metastasis stage (pM) of 0 or 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 submitted for pathological examination. Because this tissue is rarely present, the metastasis stage cannot be determined and is listed as MX.

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