Keratinizing squamous dysplasia of the oral cavity

What is keratinizing squamous dysplasia?

Keratinizing squamous dysplasia in the oral cavity is a pre-cancerous disease. Keratinizing squamous dysplasia starts from the specialized squamous cells that cover the inside of the oral cavity including the tongue, buccal mucosa, floor of mouth, hard palate, and gingiva (see picture below).

Keratinizing squamous dysplasia is considered a pre-cancerous disease because over time turn into a type of cancer called squamous cell carcinoma. Keratinizing 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 keratinizing 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).

The oral cavity

The oral cavity is the beginning of the aerodigestive tract. The oral cavity starts at the lips and ends where the mouth meets the throat. The oral cavity is made up of multiple parts including the lips, tongue, floor of mouth, gingiva, buccal mucosa, hard palate, and retromolar trigone.

Oral cavity

The inner surface of the oral cavity is covered by specialized squamous cells. that form a barrier called the epithelium. The tissue below the epithelium is called the stroma. Pathologists use the word mucosa to describe tissue that includes both the epithelium and the stroma.

Oral Cavity Normal

What causes keratinizing squamous dysplasia in the oral cavity?

The most common cause of keratinizing squamous dysplasia in the oral cavity is smoking. Other causes include excessive alcohol consumption, immune suppression, and prior radiation to the head and neck.

How do pathologists make this diagnosis?

The diagnosis of keratinizing squamous 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.

The diagnosis of keratinizing 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 usually larger and darker. 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. These squamous cells also undergo an abnormal pattern of development which results in a process called keratinization.

The abnormal cells in keratinizing 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 keratinizing squamous dysplasia.

squamous dysplasia oral cavity


Pathologists use the word grade to describe the difference between the abnormal cells in an area of keratinizing squamous dysplasia and the normal, healthy 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, squamous 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.

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 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 area of squamous dysplasia 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 abnormal area of tissue has been removed.

A negative margin means that dysplasia was not seen at any of the cut edges of tissue. A margin is called positive when there is moderate or severe keratinizing squamous dysplasia at the very edge of the cut tissue. A positive margin is associated with a higher risk that squamous dysplasia will come back at the same site after treatment.


by Jason Wasserman MD PhD FRCPC (updated July 21, 2021)
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