This article will help you read and understand your pathology report for nasopharyngeal carcinoma.
by Jason Wasserman MD PhD FRCPC, updated December 30, 2020
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 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 undergo a process called keratinization.
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. The tissue is then sent to a pathologist who examines it under a microscope.
Most patients with nasopharyngeal 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 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.
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.
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.
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.
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. Seeing 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.
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 called 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.
Tumours in the nasopharynx are often removed in multiple pieces. As a result, your pathologist may not be able to reliably assess the margins.
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.
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.
The number of lymph nodes that contain cancer cells and their location in the body is used to determine the nodal stage (see Pathologic stage below).
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 worse prognosis. The size of the largest tumour deposit is also used to determine the nodal stage (see Pathologic stage below).
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.
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.
This tumour is given a nodal stage between N0 and N3 based on the number of lymph nodes that contain cancer cells, the size of the largest tumour deposit, and the location of the lymph nodes with cancer cells.
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.