by Jason Wasserman MD PhD FRCPC
March 6, 2023

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 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.

Depth of invasion

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

Perineural invasion means that cancer cells were seen attached to a nerve. 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 important because cancer cells that have become attached to a nerve can spread into surrounding tissues by growing along the nerve. This increases the risk that the tumour will regrow after treatment.

Lymphovascular invasion

Lymphovascular invasion means that cancer cells were seen inside a blood vessel or lymphatic vessel. Blood vessels are long thin tubes that carry blood around the body. Lymphatic vessels are similar to small blood vessels except that they carry a fluid called lymph instead of blood. Lymphovascular invasion is important because cancer cells can use blood vessels or lymphatic vessels to spread to other parts of the body such as lymph nodes or the lungs.

Margins

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.