Lips, mouth, and tongue -
Keratinizing squamous dysplasia
This article was last reviewed and updated on February 25, 2019.
by Jason Wasserman, MD PhD FRCPC
Keratinizing squamous dysplasia is a precancerous disease that can involve the lips, mouth, and tongue.
Keratinizing squamous dysplasia is divided into three levels - mild, moderate, and severe - and the risk of developing cancer is highest with severe dysplasia.
The oral cavity
The lips, mouth, and tongue form an area of the body called the oral cavity. The mouth also includes the gums (gingiva), inner cheeks (buccal mucosa), and palate (the roof of the mouth).
The surface of the oral cavity is lined 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.
Some toxins such as cigarette smoke can cause the squamous cells in the epithelium to change in both look and behavior. Over time these changes lead to an abnormal pattern of growth called dysplasia. The abnormal growth often causes the cells to produce a protein called keratin and pathologists describe the tissue as showing keratinization. Together, these changes are called keratinizing squamous dysplasia.
What is keratinizing squamous dysplasia?
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).
When examined under a microscope, the abnormal cells in squamous dysplasia are only found in the epithelium on the surface of the oral cavity. In order to become squamous cell carcinoma, the cancer cells have to move from the epithelium into the stroma below. The movement of cancer cells from the epithelium into the stroma below is called invasion.
A diagnosis of squamous dysplasia means that after careful examination under the microscope, abnormal squamous cells were only found in the epithelium.
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.
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 - mild, moderate, or severe
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, moderate, or severe:
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. There is no evidence of invasion.
Pathologists often group moderate and severe dysplasia together and call them both high grade dysplasia while 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.
To emphasize the non-invasive nature of this disease, your pathology report may say that there was "no evidence of invasion" or that the tumour was "negative for invasive carcinoma".
A margin is any tissue that was cut by the surgeon in order to remove the abnormal tissue from your body. Whenever possible, surgeons will try to cut tissue outside of the abnormal area to reduce the risk that any abnormal cells will be left behind after the tissue is removed.
Your pathologist will carefully examine all the margins in your tissue sample to see how close the abnormal cells are to the edge of the cut tissue.
A margin is considered positive when there are abnormal cells at the very edge of the cut tissue. A positive margin is associated with a higher risk that the disease will come back in the same site after treatment. Most pathologists only consider moderate or severe dysplasia (high grade dysplasia) at the cut edge of the tissue to be a positive margin.
A negative margin means there were no abnormal cells at the very edge of the cut tissue. If all the margins are negative, most pathology reports will say how far the closest abnormal cells were to a margin. The distance is usually described in millimeters.
Margins will only be described in your report after the entire area of abnormal tissue has been removed.