Squamous cell carcinoma in situ of the skin

by Jason Wasserman MD PhD FRCPC
November 2, 2022


What is squamous cell carcinoma in situ?

Squamous cell carcinoma (SCC) in situ is a type of non-invasive skin cancer. The tumour starts from the cells normally found in a part of the skin called the epidermis. Another name for SCC in situ in the skin is Bowen’s disease. If left untreated, most tumours will eventually turn into a type of cancer called invasive squamous cell carcinoma.

What causes squamous cell carcinoma in situ?

Most tumours that occur in older adults develop as a result of the cells in the epidermis being damaged by UV light from the sun. Long-term exposure to UV radiation from tanning beds can cause similar damage. People who have immunosuppression due to organ transplantation or HIV infection are also at increased risk of developing SCC in situ.

Why is squamous cell carcinoma in situ of the skin called a precancerous disease?

SCC in situ is called a precancerous disease because it can turn into a type of cancer called squamous cell carcinoma over time.

Can the tumour cells in squamous cell carcinoma in situ spread to other parts of the body?

No. SCC in situ is a non-invasive type of cancer which means the tumour cells are unable to spread to other parts of the body.

How is this diagnosis made?

The diagnosis is usually made after a small tissue sample is removed in a procedure called a biopsy. The diagnosis can also be made after the entire tumour is removed in a procedure called an excision. If the diagnosis is made after a biopsy, your doctor will probably recommend a second surgical procedure to remove the rest of the tumour.

What does squamous cell carcinoma in situ look like under a microscope?

When examined under the microscope, the tumour cells in SCC in situ are larger and darker than the squamous cells normally found in the epidermis of the skin. Pathologists often describe these abnormal-looking squamous cells as atypical or pleomorphic. In order to make the diagnosis of SCC in situ, the tumour cells should only be seen in the epidermis. In contrast, in squamous cell carcinoma, the tumour cells have broken through the basement membrane and spread into the dermis below.

squamous cell carcinoma and in situ

What is a margin?

In pathology, a margin is the edge of a tissue that is cut when removing a tumour from the body. The margins described in a pathology report are very important because they tell you if the entire tumour was removed or if some of the tumour was left behind. The margin status will determine what (if any) additional treatment you may require.

Most pathology reports only describe margins after a surgical procedure called an excision or resection has been performed for the purpose of removing the entire tumour. For this reason, margins are not usually described after a procedure called a biopsy is performed for the purpose of removing only part of the tumour. The number of margins described in a pathology report depends on the types of tissues removed and the location of the tumour. The size of the margin (the amount of normal tissue between the tumour and the cut edge) depends on the type of tumour being removed and the location of the tumour.

Pathologists carefully examine the margins to look for tumour cells at the cut edge of the tissue. If tumour cells are seen at the cut edge of the tissue, the margin will be described as positive. If no tumour cells are seen at the cut edge of the tissue, a margin will be described as negative. Even if all of the margins are negative, some pathology reports will also provide a measurement of the closest tumour cells to the cut edge of the tissue.

A positive (or very close) margin is important because it means that tumour cells may have been left behind in your body when the tumour was surgically removed. For this reason, patients who have a positive margin may be offered another surgery to remove the rest of the tumour or radiation therapy to the area of the body with the positive margin.

Margin

What does it mean if my report says the tumour was incompletely excised?

Incompletely excised means that only part of the tumour was removed from the body. Pathologists describe a tumour as being incompletely excised when tumour cells are seen at the edge of the tissue. In pathology, the cut edge of the tissue is also called the margin. It is normal for a tumour to be incompletely excised after a small procedure such as a biopsy because these procedures are usually not performed to remove the entire tumour. However, larger procedures such as excisions and resections are usually performed to remove the entire tumour. If a tumour is incompletely excised, your doctor may recommend another procedure to remove the rest of the tumour.

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