Sebaceous carcinoma

What is sebaceous carcinoma?

Sebaceous carcinoma is a type of skin cancer. Sebaceous carcinoma develops from specialized cells called sebocytes in the dermis and subcutaneous tissue of the skin. One of the most common locations for sebaceous carcinoma is in the skin around the eye. The cancer cells produce a fatty substance called sebum which often makes the tumour look yellow.

Skin

The outside of our body is covered in skin. The surface of the skin is called the epidermis. The epidermis produces a material called keratin. The epidermis is waterproof and protects us from toxins and injuries. The tissue beneath the epidermis is called the dermis, it contains blood vessels and connective tissue.

Below the dermis is a layer of subcutaneous fat. The epidermis is separated from the dermis and subcutaneous fat by a very thin layer of tissue called the basement membrane. Located within the dermis and subcutaneous tissue are small structures called adnexa. The adnexa in the skin include follicles that make hair and glands that produce sweat to keep us cool and oil to help keep our skin waterproof.

Sebaceous glands

Sebaceous glands are a type of gland found in the skin adnexa.  Sebaceous glands make and secrete a material called sebum which looks and feels like fat. Too much sebum can make our skin and hair feel greasy.

Sebaceous glands can be found all over the body although the greatest number are found on the face and scalp. There are no sebaceous glands found on the palms of our hands or soles of our feet. Sebaceous glands are made up of cells called sebocytes. Under the microscope, sebocytes can be seen producing the fat that is used to make sebum.

What causes sebaceous cell carcinoma?

Sebaceous carcinoma is an uncommon type of skin cancer and doctors still do not know what causes most tumours. However, for some patients, previous radiation has been shown to increase the risk for sebaceous carcinoma in the exposed area of the body.

Muir Torre syndrome

People with Muir Torre syndrome are at an increased risk of developing sebaceous carcinoma. These people tend to develop multiple sebaceous carcinomas and the tumours are larger than in a patient without the syndrome. People with Muir Torre syndrome also have an increased risk of developing colon cancer. If you have been diagnosed with multiple sebaceous carcinomas, your doctor may suggest a genetic test to see if you have Muir Torre syndrome.

How do pathologists make this diagnosis?

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.

Margins

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 cancer cells are to the edge of the cut tissue. Margins will only be described in your report after the entire tumour has been removed.

A negative margin means there were no cancer cells at the very edge of the cut tissue. If all the margins are negative, most pathology reports will say how far the closest cancer cells were to a margin. The distance is usually described in millimetres.

A margin is considered positive when there are cancer cells at the very edge of the cut tissue. A positive margin is associated with a higher risk that the tumour will recur in the same site after treatment.

by Allison Osmond, MD FRCPC (updated August 19, 2021)