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 mouth 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 (a non-invasive malignant tumour). 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 movement 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 (there was no evidence of invasion).

The diagnosis of squamous carcinoma in situ is usually made on a biopsy and an excision or resection is then performed to remove the abnormal tissue and to look for evidence of invasion.

Tumour size
These tumours are measured in three dimensions but only the largest dimension is typically included in the report. For example, if the tumour measures 3.0 cm by 1.0 cm by 0.2 cm, the report may describe the tumour size as 3.0 cm in greatest dimension.

Tumour size will only be described in your report after the entire tumour has been removed.

Squamous carcinoma in situ is a non-invasive form of cancer (a non-invasive malignant tumour). That means that after careful examination of your tissue sample under the microscope, your pathologist only saw cancer cells in the epithelium on the inner surface of the oral cavity.


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 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.

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.

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.

Margins will only be described in your report after the entire tumour has been removed.

Lymph nodes
Metastatic disease describes the process where tumour cells escape the main tumour and travel to another part of the body. Lymph nodes are small immune organs located throughout the body, are a common target for metastatic disease.


Many patients with a diagnosis of squamous carcinoma in situ will not have any lymph nodes removed and sent for pathological examination. However, some patients may undergo a procedure called a neck dissection where the surgeon removes lymph nodes normally found in the neck.


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 submitted for examination.


Most reports include the total number of lymph nodes examined and the number that contain tumour cells. A group of tumour cells inside a lymph node is called a tumour deposit. Your pathologist will measure each tumour deposit and the largest deposit at each neck level will be included in your report.

Laterality refers to whether the lymph node is on the same side as the tumour (ipsilateral) or the opposite side of the tumour (contralateral).


All lymph nodes are surrounded by a capsule. Extracapsular extension means that tumour cells have broken through the capsule and into the tissue that surrounds the lymph node. Extracapsular extension is also associated with a higher risk of new tumours developing in the neck and is often used by your doctors to guide your treatment.

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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