What is this tumor?
This tumor 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 tumors are benign and can be permanently cured by total surgical removal. Many are multiple. Malignant tumors, 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 that come together for the unfortunate individual.
We do not know precisely what causes these tumors but there is a genetic predisposition in some breeds of dog. Induction of cancer is a multi-step process called tumor progression. The majority of sebaceous gland tumors 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 tumors (adenomas and epitheliomas) grade into each other.
Is this a common tumor?
These are common tumors in dogs, mainly in middle aged to older animals with a mean age of occurrence of 10 years. The tumors frequently occur at multiple sites on the same animal. Tumors are most frequently found on the head. They are often mistaken for "warts". There is a breed predilection that includes Cocker Spaniels.
Many tumors are on the eyelids where they originate from the Meibomian sebaceous-type glands. These are classified as a separate group although the tumors are identical in type and behaviour to those in other areas.
How will this tumor affect my dog?
The tumors 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 tumor diagnosed?
Clinically, tumors 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 (histopathology). This is done at a specialized 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 tumor has been fully removed. Histopathology rules out other more serious cancers.
What treatment is available?
Treatment is surgical removal of the lump.
Can this tumor 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 tumor to regress.
How can I nurse my dog?
Preventing your pet from rubbing, scratching, licking or biting the tumor 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 or significant swelling or bleeding should be reported to your veterinarian. If you require additional advice on post-surgical care, please ask.
How will I know if the tumor is permanently cured?
’Cured’ has to be a guarded term in dealing with any tumor.
Histopathology will give your veterinarian the diagnosis that helps to indicate how the tumor is likely to behave. The veterinary pathologist usually adds a prognosis that describes the probability of local recurrence or metastasis (distant spread) of the tumor.
Sebaceous gland hyperplasia and sebaceous gland adenoma are benign tumors. They do not recur following excision although some animals can have multiple tumors, so further tumors 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.
Based on material written by Joan Rest, BVSc, PhD, MRCPath, MRCVS. and modified with permission from Lifelearn Inc.
© Copyright 2004 Lifelearn Inc.
