Squamous carcinoma in situ of the oral cavity

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

by Jason Wasserman, MD PhD FRCPC, updated March 18, 2021

Quick facts:

• Squamous carcinoma in situ (CIS) is a type of non-invasive cancer that starts in the oral cavity.
• The oral cavity includes the lip, tongue, floor of mouth, inner cheeks, and gums.
• Without treatment, patients with squamous carcinoma in situ are at high risk for developing a type of invasive oral cavity cancer called squamous carcinoma.

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 (see picture below).

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.

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 the stroma. Pathologists use the word mucosa to describe tissue that includes both the epithelium and the stroma.

What is squamous carcinoma in situ (CIS)?

Squamous carcinoma in situ is a type of non-invasive cancer. The tumour starts from the squamous cells on the inner surface of the oral cavity. Another name for squamous carcinoma in situ is severe squamous dysplasia.

If left untreated, squamous carcinoma in situ almost always turns into a type of invasive cancer called squamous cell carcinoma. Squamous carcinoma in situ can start in any part of the oral cavity although the most common location is the lateral border of the tongue.

What is the difference between squamous carcinoma in situ and squamous cell carcinoma?

The abnormal cells in squamous carcinoma in situ 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 carcinoma in situ.

What causes squamous carcinoma in situ in the oral cavity?

The most common cause of squamous carcinoma in situ 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 squamous carcinoma in situ 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 squamous carcinoma in situ 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 carcinoma in situ 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 commonly undergo an abnormal pattern of development which results in a process called keratinization.

What to look for in your report after the tumour is removed

Tumour size

This is the size of the tumour measured in centimetres. The tumour is usually measured in three dimensions but only the largest dimension is described in your report. For example, if the tumour measures 2.0 cm by 1.5 cm by 1.2 cm, your report will describe the tumour as being 2.0 cm.

Margins

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 tumour 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 negative margin means there were no tumour cells at the very edge of the cut tissue. If all the margins are negative, most pathology reports will say how far the closest tumour cells were to a margin. The distance is usually described in millimetres.

A margin is considered 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 come back (recur) in the same site after treatment.