Lip, mouth, and tongue -

Squamous carcinoma in situ

This article was last reviewed and updated on February 25, 2019.
by Jason Wasserman, MD PhD FRCPC

Quick facts:

  • Squamous carcinoma in situ (CIS) is a type of non-invasive cancer that can involve the lips, mouth, and tongue. 

  • It is called non-invasive because after careful examination of your tissue sample under the microscope, your pathologist only saw cancer cells on the outer surface of the tissue.

  • Without treatment, patients with squamous carcinoma in situ are at high risk for developing a type of invasive cancer called squamous carcinoma.

The oral cavity

The lips, mouth, and tongue form an area of the body called the oral cavity. The oral cavity also includes the gums (gingiva), inner cheeks (buccal mucosa), and palate (the roof of the mouth).

The surface of the lips, mouth, and tongue are lined by cells called squamous cells. that create a barrier on the outside of the tissue 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 can lead to a disease called squamous carcinoma in situ. 

What is squamous carcinoma in situ (CIS)?

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


Squamous cells in carcinoma in situ is called a non-invasive disease because the abnormal cells are seen only in the epithelium. The spread of abnormal cells from the epithelium into the stroma is called invasion. A diagnosis of squamous carcinoma in situ means that your pathologist did not seen any abnormal cells in the stroma.

The first diagnosis of squamous carcinoma in situ is usually made after a small sample of tissue is removed in a procedure called a biopsy. A surgical procedure is then performed to remove the abnormal tissue and to look for invasion.

Tumour size

This is the size of the tumour measured in centimeters. 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.


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 margin is considered positive when there are tumour cells at the very edge of the cut tissue. 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 millimeters.

Why is this important? A positive margin is associated with a higher risk that the tumour will come back (recur) in the same site after treatment.

Lymph nodes

Lymph nodes are small immune organs located throughout the body. Tumour cells can travel from the tumour to a lymph node through lymphatic channels located in and around the tumour. The movement of tumour cells from the tumour to a lymph node is called a metastasis.


Lymph nodes are not always removed for squamous carcinoma in situ. When lymph nodes are removed at the same time as the tumour, they are usually fro the neck and the procedure is 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 tumour cells. Lymph nodes that contain tumour cells are often called positive while those that do not contain any tumour cells are called negative. Most reports include the total number of lymph nodes examined and the number, if any, that contain tumour cells.

Why is this important? Because squamous carcinoma in situ is a non-invasive disease, it is very unlikely that cancer cells will be found in any of the lymph nodes examined.

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