Tonsils, base of tongue, and soft palate -
Squamous cell carcinoma
This article was last reviewed and updated on August 19, 2019.
by Jason Wasserman, MD PhD FRCPC
The tonsils, base of tongue, and soft palate form an area called the oropharynx.
Squamous cell carcinoma is a type of throat cancer that starts in the oropharynx.
Most tumours in this area are caused by a virus called human papillomavirus (HPV).
Pathologists look HPV in cancer cells by performing a test for a protein called p16.
The tonsils, base of tongue, and soft palate form an area of the body called the oropharynx. The oropharynx includes special tissue that is designed to help protect us from infections that may try to enter our body through our mouth or nose.
The surface of the oropharynx is lined by squamous cells that form a barrier called the epithelium. The tissue below the epithelium is called stroma. The stroma in the oropharynx is made up mostly of immune cells which makes this tissue look very similar to a lymph node.
What is squamous cell carcinoma?
Squamous cell carcinoma is a type of throat cancer. The tumour develops from the squamous cells in the epithelium of the oropharynx.
Squamous cell carcinoma is the most common type of cancer in the oropharynx. Most of these tumours are called non-keratinizing squamous cell carcinoma because the tumour cells do not make a protein called keratin that is made by squamous cells in other parts of the body.
Most cases of squamous cell carcinoma in the oropharynx are caused by a virus called human papillomavirus (HPV). This virus infects the squamous cells and over time changes them into cancer cells.
Even through the tumour starts in the oropharynx, the cancer cells commonly spread to lymph nodes in the neck. The movement of cancer cells from the main tumour to a lymph node or other area of the body is called metastasis. When this happens, you may notice an abnormal lump or growth in your neck.
The diagnosis of squamous cell carcinoma is usually made after a small tissue sample is removed in a procedure called a biopsy. The biopsy may be taken from the oropharynx or it may be taken from the neck.
For some patients, surgery may be performed to remove the entire tumour. Other patients may receive radiation therapy with or without surgery to remove the tumour. Your doctor will discuss the treatment options with you and help you pick the option that is best for you.
This is the size of the tumour. Tumour size will only be described in your report after the entire tumour has been removed. The tumour is usually measured in three dimensions but only the largest dimension is described in your report. For example, if the tumour measures 4.0 cm by 2.0 cm by 1.5 cm, your report will describe the tumour as being 4.0 cm.
Why is this important? The tumour size is used to determine the tumour stage (see Pathologic stage below). Larger tumours are associated with worse prognosis.
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.
Why is this important? Cancer cells that have attached to a nerve can use the nerve to travel into tissue outside of the original tumour. This increases the risk that the tumour will come back in the same area of the body (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.
Why is this important? 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. Margins will only be described in your report after the entire tumour has been removed.
A margin is considered positive when there are cancer cells at the very 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 say how far the closest cancer cells were to a margin. The distance is usually described in millimeters.
Why is this important? A positive margin is associated with a higher risk that the tumour will grow back (recur) in the same site after treatment.
p16 is a protein that is produced by both normal and abnormal cells. Pathologists perform a special test called immunohistochemistry in order to be able to see the p16 protein inside cells.
Tumours made up of cells that produce extra p16 are described as positive (or reactive) while those that do not produce extra p16 are reported as negative (non-reactive).
Cancer cells that have been infected with human papillomavirus produce extra p16 which builds up inside the cancer cells. For this reason, most squamous cell carcinomas in the oropharynx are positive (reactive) for p16.
Why is this important? This test result will be used by your other doctors to guide your treatment because p16 positive tumours respond better to radiation compared to p16 negative tumours.
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.
Why is this important? The number of lymph nodes that contain cancer cells 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.
Why is this important? The size of the tumour deposit is only important for tumours not caused by HPV (p16 negative tumours). For these tumours, 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).
Extranodal extension (ENE)
All lymph nodes are surrounded by a capsule. Extranodal extension (ENE) means that cancer cells have broken through the capsule and into the tissue that surrounds the lymph node.
Why is this important? Extranodal extension is only important for tumours not caused by HPV (p16 negative tumours). For these tumours, extranodal extension is also associated with a higher risk of new tumours developing in the neck and is often used by your doctors to guide your treatment. Extranodal extension is also used to determine the nodal stage (see Pathologic stage below).
Pathologic stage (pTNM)
The pathologic stage for squamous cell 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.
The pathologic stage will only be included in your report after the entire tumour has been removed.
Tumour stage (pT) for squamous cell carcinoma
Squamous cell carcinoma of the oropharynx is given a tumour stage between 1 and 4. The tumour stage is based on the size of the tumour and whether the tumour has grown to include parts of the mouth or throat outside of the oropharynx.
T1 - The tumour is 2 cm or smaller.
T2 - The tumour is greater than 2 cm but not larger than 4 cm.
T3 - The tumour is larger than 4 cm but is still only located within the oropharynx.
T4 - The tumour has spread into tissues outside of the oropharynx such as the deep muscles of the tongue, the larynx, or the bone of the lower jaw (the mandible).
Nodal stage (pN) for squamous cell carcinoma
Tumours that are associated with HPV or that test positive for p16 are given an nodal stage between 0 and 2 based on the number of lymph nodes that contain cancer cells.
N0 - No cancer cells are found in any of the lymph nodes examined.
N1 - Cancer cells are found in 1 to 4 lymph nodes examined.
N2 - Cancer cells are found in more than 4 lymph nodes examined.
Metastatic stage (pM) for squamous cell carcinoma
These tumours are given a metastatic 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 assigned if tissue from a distant site is submitted for pathological examination. Because this tissue is rarely present, the metastatic stage cannot be determined and is listed as pMX.