Basosquamous carcinoma of the skin

by Jason Wasserman MD PhD FRCPC
May 27, 2022


What is basosquamous carcinoma?

Basosquamous carcinoma is a type of skin cancer. It is a more aggressive variant of basal cell carcinoma. In addition to the typical features of basal cell carcinoma, basosquamous carcinoma also shows features of another type of skin cancer called squamous cell carcinoma. The tumour starts from specialized basal cells found near the surface of the skin.

What causes basosquamous carcinoma?

Prolonged and excessive exposure to UV radiation from the sun is the most common cause of basosquamous carcinoma. Because they are constantly dividing, basal cells are more sensitive to DNA damage caused by long-term exposure to UV radiation from the sun.

How do pathologists make the diagnosis of basosquamous carcinoma?

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 the depth of invasion mean and why is it important?

Basosquamous carcinoma starts in a layer of the skin called the epidermis. The layers below the epidermis are called the dermis and subcutaneous tissue. Pathologists use the term depth of invasion to describe how far the tumour cells have spread from the epidermis into the layers of tissue below (the dermis and subcutaneous tissue). For skin tumours, the depth of invasion is measured from the surface of the skin to the deepest point of invasion. Some pathology reports describe the depth of invasion as tumour thickness. Tumours that grow deeper into the dermis are more likely to spread to a lymph node or to grow back after treatment. The depth of invasion is usually only reported after the entire tumour has been removed.

Perineural invasion

Nerves are like long wires made up of groups of cells called neurons. Nerves are found all over the body and they are responsible for sending information (such as temperature, pressure, and pain) between your body and your brain. Perineural invasion is a term pathologists use to describe tumour cells attached to a nerve. Perineural invasion is important because tumour cells that have become attached to a nerve can grow along the nerve and into surrounding tissues. This increases the risk that the tumour will re-grow after treatment.

perineural invasion

Lymphovascular invasion

Blood moves around the body through long thin tubes called blood vessels. Another type of fluid called lymph which contains waste and immune cells moves around the body through lymphatic channels. The term lymphovascular invasion is used to describe tumour cells that are found inside a blood vessel or lymphatic channel. Lymphovascular invasion is important because once the tumour cells are inside a blood vessel or lymphatic channel they are able to metastasize (spread) to other parts of the body such as lymph nodes or the lungs.

lymphovascular invasion

What is a margin?

A margin is a rim of normal tissue that surrounds a tumour and is removed with the tumour at the time of surgery. The margins are usually only described in a pathology report after an excision has been performed to remove the tumour. Margins are often not described after a biopsy.

When examining a basosquamous carcinoma under the microscope, a margin is considered positive when there is no distance between the tumour cells and the cut edge of the tissue. A margin is called negative when there are no tumour cells at the cut edge of the tissue. A positive margin is associated with a higher risk that the tumour will re-grow in the same site after treatment.

 

Margin

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