Cat & Dog - Sebaceous Gland Tumours

These notes are provided to help you understand the diagnosis or possible diagnosis of cancer in your pet. For general information on cancer in pets ask for our handout What is cancer.  If not already performed your veterinary surgeon may suggest certain tests to help confirm or eliminate the diagnosis, and to help assess treatment options and likely outcomes. Because individual situations and responses vary, and because cancers often behave unpredictably, science can only give us a guide. However information and understanding of tumours in animals is improving all the time.

We understand that this can be a very worrying time and we apologise for the need to use some technical language. If you do not understand anything, please do not hesitate to ask.

What is this tumour?

This tumour is a disordered and purposeless overgrowth of sebaceous gland cells. These glands are attached to the hair follicles where their function is to lubricate the hairs and skin. Almost all sebaceous gland tumours are benign and can be permanently cured by total surgical removal. Many are multiple. Malignant tumours, which have the potential to spread to other parts of the body, are extremely rare.

What do we know about the cause?

The reason why a particular pet may develop this, or any cancer, is not straightforward. Cancer is often seemingly the culmination of a series of circumstances which come together for the unfortunate individual.

We do not know precisely what causes these tumours but there is a genetic predisposition in some breeds of dog. Induction of cancer is a multi-step process called tumour progression. The majority of sebaceous gland tumours never progress past the first stages and are technically hyperplasias (overgrowths) rather than true, out-of-control cancers. Nodular sebaceous hyperplasia (the first phase) and benign sebaceous tumours (adenomas and epitheliomas) grade into each other.

Is this a common tumour?

These tumours are rare in cats but common in dogs, mainly in middle aged to older animals with an average age occurrence of 10 years. The tumours frequently occur at multiple sites on the same animal. Tumours are most frequently found on the head. They are often mistaken for 'warts'. There is a breed predilection that includes Cocker Spaniels.

Many tumours are on the eyelids where they originate from the Meibomian sebaceous-type glands. These are classified as a separate group although the tumours are identical in type and behaviour to those in other areas.

How will this cancer affect my animal?

The tumours are typically polyp-like (i.e a protruding mass on a narrower base). They are frequently multiple and 2-5 mm in diameter. They often itch, become inflamed and ulcerated and may be secondarily infected.

How is the tumour diagnosed?

Clinically, tumours have a fairly typical appearance but accurate diagnosis relies upon microscopic examination of tissue. Cytology (the microscopic examination of aspirated cell samples) is used for rapid or preliminary tests. More accurate diagnosis and prediction of behaviour (prognosis) usually relies upon microscopic examination of tissue samples (histopathology). This is done at a specialised laboratory by a veterinary pathologist. The piece of tissue may be a small part of the mass (biopsy) or the whole lump. The information from the whole lump will also indicate whether the tumour has been fully removed. Histopathology rules out other more serious cancers.

What treatment is available?

Treatment is surgical removal of the lump.

Can this cancer disappear without treatment?

Cancer very rarely disappears without treatment. Very occasionally, spontaneous loss of blood supply to the cancer can make it die but the dead tissue will still need surgical removal. The body's immune system is not effective in causing this type of tumour to regress.

How can I nurse my pet?

Preventing your pet from rubbing, scratching, licking or biting the tumour will reduce itching, inflammation, ulceration, infection and bleeding. Any ulcerated area needs to be kept clean.

After surgery, the operation site similarly needs to be kept clean and your pet should not be allowed to interfere with the site. Any loss of sutures (stitches) or significant swelling or bleeding should be reported to your veterinary surgeon. If you require additional advice on post-surgical care, please ask.

How will I know if the cancer is permanently cured?

Histopathology will give your veterinary surgeon the diagnosis that helps to indicate how the tumour is likely to behave. The veterinary pathologist usually adds a prognosis that describes the probability of local recurrence or metastasis (distant spread) of the tumour.

Sebaceous gland hyperplasia and sebaceous gland adenoma are benign tumours. They do not recur following excision (removal) although some animals can have multiple tumours, so further tumours may develop at different sites. Sebaceous epitheliomas occasionally recur locally.

The rare sebaceous carcinomas infiltrate the surrounding tissue but can still be cured surgically. Metastasis is very rare.

Are there any risks to my family or other pets?

No, these are not infectious and are not transmitted from pet to pet or from pets to people.