Pathology dictionary

What is squamous cell carcinoma?

Squamous cell carcinoma (SCC) is a type of cancer made up of specialized cells called squamous cells. It can start anywhere that squamous cells are normally found including the skin, mouth, lungs, and cervix.

What are squamous cells?

Squamous cells are a specialized type of cell that are normally found on the surface of a tissue. The squamous cells create a barrier which protects the tissue below the surface from infections and injuries. Squamous cell can be found on the outer surface of a tissue such as the skin or the inner surface of a tissue such as the esophagus. The barrier created is called the epithelium.

Squamous cell carcinoma

SCC is a very common type of cancer. One of the reasons it is so common is because it can start anywhere squamous cells are normally found. When examined under the microscope, the tumour looks similar regardless of where in the body it started.

Some common locations for SCC include:

What causes squamous cell carcinoma?

The cause depends on the location in the body where the tumour starts. Chemicals, especially those found in cigarette smoke, are associated with the development of SCC in the tongue, esophagus, larynx, and lungs.

A virus called human papillomavirus infects cells in the tonsils and cervix and is the cause for almost all cases of SCC in these locations.

Ultraviolet light from the sun causes most cases of SCC in the skin.

Some tumours start from a pre-cancerous disease called squamous carcinoma in situ. This pre-cancerous tumour may be present for months or years before changing into a type of cancer.

Tumour grade

Pathologists use the word grade to describe the difference between the tumour cells in SCC and normal, healthy squamous cells. The grade is then usually divided into three levels – mildly, moderately, and poorly differentiated. Using this system, mildly differentiated tumour cells look the most like normal squamous cells. In contrast, poorly differentiated tumour cells look the least like normal squamous cells.

Keratinizing and non-keratinizing tumours

Squamous cell carcinoma can also be described as keratinizing if the tumour produces a special type of protein called keratin which is normally found on the surface of the skin. Tumours that do not produce keratin are called non-keratinizing squamous cell carcinoma.

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