Squamous dysplasia - Oral cavity -

This article will help you read and understand your pathology report for squamous dysplasia of the oral cavity.

by Jason Wasserman, MD PhD FRCPC, reviewed on March 6, 2020

Quick facts:
  • Squamous dysplasia is a pre-cancerous disease that starts in the oral cavity.
  • The oral cavity includes the lips, mouth, tongue, gums, and inner cheeks.
  • It is called a pre-cancerous disease because overtime it can turn into a type of cancer called squamous cell carcinoma.
  • Squamous dysplasia is divided into mild, moderate, and severe, and the risk of developing cancer is highest with severe dysplasia.
The anatomy of the oral cavity

The oral cavity is the beginning of the aerodigestive tract. It is used for both breathing and taking in food. The oral cavity is a complex area of the body that is made up of many parts.

The oral cavity includes:

  • Lips – The soft inner surface of the lips are part of the oral cavity. The outer surface of the lips are covered by skin and are not considered part of the oral cavity.
  • Tongue – The part of the tongue that you can see when you look in your mouth is part of the oral cavity. The very back of the tongue (the part you can’t see) is part of another area of the body called the oropharynx.
  • Floor of mouth – The floor of mouth is the soft tissue underneath your tongue.
  • Cheeks – The inner surface of the cheeks are part of the oral cavity. The inner cheeks are also called the buccal mucosa.
  • Gums – The gums are the tissue that surround and hold the teeth. The gums are also called gingiva.
  • Roof of mouth – This is the top of your mouth. Only the hard part of the roof is part of the oral cavity. The soft part of the roof at the very back of your mouth near your throat is called the soft palate and it is part of another area of the body called the oropharynx.
  • Retromolar trigone – This is a small triangle shaped area of tissue behind the last tooth on the bottom of your mouth.

Oral cavity

The inner surface of the oral cavity is covered by cells called squamous cells. that form a barrier 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.

normal squamous mucosa

What is squamous dysplasia?

Squamous dysplasia in the oral cavity is a pre-cancerous disease.  It is called pre-cancerous because it can over time turn into a type of cancer called squamous cell carcinoma. Squamous dysplasia can start in any part of the oral cavity although the most common location is the lateral border of the tongue.

The risk associated with squamous dysplasia turning into cancer depends on how abnormal the squamous cells look under the microscope. The risk of cancer is highest when your pathologist describes the changes as severe (see Grade below).

What causes squamous dysplasia in the oral cavity?

The most common cause of squamous dysplasia in the oral cavity is smoking. Other causes include excessive alcohol consumption, immune suppression, and prior irradiation. Smoking in particular causes the squamous cells to undergo an abnormal pattern of development which results in a process called keratinization. Because of this, some pathology reports will describe this condition as “keratinizing squamous dysplasia”.

How do pathologists make this diagnosis?

The diagnosis of squamous dysplasia can only be made after a tissue sample is examined under the microscope. Compared to normal, healthy squamous cells, the abnormal cells in an area of squamous dysplasia are larger, darker, and disorganized. Pathologists use the word hyperchromatic to describe cells that look darker than normal cells. Large clumps of genetic material called nucleoli may also be seen in the nucleus of the abnormal cells.

The abnormal cells in squamous dysplasia are only seen in the epithelium. This is different from squamous cell carcinoma where the abnormal cells are also seen in the stroma below the epithelium. The movement of abnormal cells from the epithelium into the stroma is called invasion. Your pathologist will carefully examine your tissue sample to make sure there is no evidence of invasion before making the diagnosis of squamous dysplasia.

The diagnosis of dysplasia is usually made after a small sample of tissue is removed in a procedure called a biopsy. The biopsy is usually performed because you or your doctor saw an abnormal looking area of tissue within your oral cavity. Your pathology report will probably say what part of the oral cavity was sampled in the biopsy.

Depending on the grade of the disease (see Grade below), your doctor may recommend surgery to remove all of the abnormal tissue or close clinical follow-up.


Grade is a word pathologists use to describe how different the abnormal cells in an area of dysplasia look compared to the normal squamous cells that are usually found in the oral cavity.

Pathologists use the size, colour, and shape of the cell to determine the grade. Using these features, dysplasia in the oral cavity is usually divided into three levels:

  • Mild dysplasia – The abnormal squamous look very similar to normal squamous cells.
  • Moderate dysplasia – The abnormal squamous cells are darker and larger than normal squamous cells and the normal organization of the epithelium may be disrupted.
  • Severe dysplasia – The abnormal squamous cells look similar to cancer cells but they are still only seen in the epithelium. Another name for severe dysplasia is squamous carcinoma in situ.

Oral cavity dysplasia carcinoma in situ

Some pathology reports will group moderate and severe dysplasia together and call them both high grade dysplasia. Mild dysplasia is called low grade dysplasia.

The grade is very important because it is related to the risk of developing an invasive cancer in the future. Mild (low grade) dysplasia has a very low risk of turning into cancer and is often left untreated. Moderate and severe (high grade) dysplasia is associated with a much higher risk of becoming cancer and patients with this condition are usually offered treatment to remove the diseased tissue.


A margin is any tissue that was cut by the surgeon in order to remove the tumour from your body. The types of margins described in your report will depend on the organ involved and the type of surgery performed. Margins will only be described in your report after the entire tumour has been removed.

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. A negative margin means that no tumour cells were seen at any of the cut edges of tissue.

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