This article was last reviewed and updated on June 23, 2019.
by Jason Wasserman, MD PhD FRCPC
Nasopharyngeal carcinoma is a cancer that starts from the tissue that lines the back of the nose and throat.
Another name for nasopharyngeal carcinoma is non-keratinizing squamous cell carcinoma.
Most cases of nasopharyngeal carcinoma are caused by a virus called Epstein-Barr virus (EBV).
The nasopharynx is part of an area of the body called the upper aerodigestive tract. The nasopharynx is located where the inside of the nose (the nasal cavity) meets the back of the throat (the pharynx).
The nasopharynx is lined by cells called squamous cells. These cells form a barrier on the surface of the nasopharynx called the epithelium. The tissue below the epithelium is called stroma. Pathologists use the word mucosa to describe tissue that includes both the epithelium and the stroma.
Nasopharyngeal carcinoma is a type of cancer (a malignant tumour) that develops from the squamous cells in the epithelium. This tumour is also called non-keratinizing squamous cell carcinoma because unlike squamous cells in other parts of the body, the cancer cells do not produce large amount of a protein called keratin.
Most cases of nasopharyngeal carcinoma are associated with a virus known as Epstein-Barr virus (EBV) which infects the squamous cells and causes them to change into cancer cells.
The diagnosis of nasopharyngeal carcinoma is usually made after a small sample of tissue is removed from your body in a procedure called a biopsy. Most patients with non-keratinizing squamous cell carcinoma will be treated with radiation although you may be offered surgery first to remove the tumour.
If you had surgery to remove the tumour from your body, your pathologist will attempt to measure the tumour and this measurement will be included in your report. For example, if the tumour measures 5 cm x 3 cm x 1 cm, the report may describe the tumour size as 5 cm in greatest dimension.
Tumours in the nasopharynx are often removed in multiple pieces. As a result, your pathologist may not be able to accurately measure the tumour size. In this case, an approximate tumour size may be described.
Tumour size will only be described in your report after the entire tumour has been removed.
Nerves are like long wires made up of groups of cells called neurons. Nerves transmit information (such as temperature, pressure, and pain) between your brain and your body. Perineural invasion is a term pathologists use to describe cancer cells 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. For this reason, perineural invasion is associated with a higher risk that the tumour will come back in the same area of the body (local recurrence) after treatment.
Lymphatics and blood vessels are long tubes that allow fluid (lymph and blood, respectively) and cells to travel around the body. When cancer cells enter a lymphatic or blood vessel it is called lymphovascular invasion and is associated with a higher risk that cancer cells will travel (metastasize) to a lymph node or a distant site such as 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.
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 margin is considered positive when there are cancer 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.
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 say how far the closest cancer cells were to a margin. The distance is usually described in millimeters.
Margins will only be described in your report after the entire tumour has been removed.
Cells infected by Epstein-Barr virus produce a chemical called Epstein-Barr virus-encoded small RNA or EBER for short. Pathologists use a special test called in situ hybridization (ISH) to look for cells that are producing EBER.
Most nasopharyngeal carcinomas produce EBER. Your report will describe the tumour as ‘positive’ if EBER is seen inside the cancer cells and ‘negative’ if no EBER is seen.
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 a metastasis.
Your pathologist will carefully examine all lymph nodes for cancer cells. Most reports include the total number of lymph nodes examined and the number, if any, that contain 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.
Lymph nodes on the same side as the tumour are called ipsilateral while those on the opposite side of the tumour are called contralateral.
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.
A tumour deposit is a group of cancer cells found inside a lymph node. If cancer cells are found in a lymph node, your pathologist will measure the size of the tumour deposit and this measurement will be included in your report.
Pathologic stage (pTMN)
The pathologic stage for nasopharyngeal 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 worse prognosis.
Tumour stage (pT) for nasopharyngeal carcinoma
This tumour is given a tumour stage between 1 and 4. The tumour stage is based on how far the tumour has spread outside of the nasopharynx.
T1 - The tumour is only seen in the nasopharynx OR it has only spread to the oropharynx or nasal cavity.
T2 – The tumour has spread outside of the nasopharynx into the soft tissues or muscles that surround the nasopharynx.
T3 - The tumour has spread into the bones of the skull, the sinuses, or the bones of spine.
T4 - The tumour has spread to the eyes, the large nerves of the head known as the cranial nerves, the parotid gland, or beyond the skull into the cranial cavity (the cavity that holds the brain).
Nodal stage (pN) for nasopharyngeal carcinoma
This tumour is given a nodal stage between 0 and 3 based on the following two features:
The size of the tumour deposit (see Lymph nodes above).
Whether the lymph nodes with cancer cells are on the same side (ipsilateral) or the opposite side (contralateral) of the tumour.
If no cancer cells are found in any of the lymph nodes examined, the nodal stage is pN0.
If no lymph nodes are sent for pathological examination, the nodal stage cannot be determined and the nodal stage is listed as pNX.
Metastatic stage (pM) for nasopharyngeal carcinoma
Nasopharyngeal carcinoma is given an metastatic stage 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 assigned if tissue from a distant site is sent for pathological examination. Because this tissue is rarely present, the metastatic stage cannot be determined and is listed as MX.