Dog - Anal Sac 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 cells originating from the modified sweat glands of an anal sac. There are a pair of anal sacs, one each side of the anus between the external and internal anal sphincter. The glands normally produce bad-smelling grey-brown granular secretions. The tumour is usually rapidly growing, almost always malignant (spreading), and extends deep into surrounding tissues. There can be abnormal hormone production by the tumour cells and these hormones can cause widespread physiological effects in the animal. The malignant tumour (anal gland carcinoma) may also spread to other parts of the body (metastasise).

What do we know about the cause?

We do not know what causes this tumour. 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.

Is this a common tumour?

No. The malignant form of the tumour (carcinoma) is uncommon in dogs and rare in cats. Benign (non-invasive) forms of this tumour are almost unknown.

How will this cancer affect my animal?

The tumour may be noticed as a lump beside the anus but growth is often inwards so the lump may not appear as large as the actual tumour. Anal sac dimension and the colour and consistency of its content are highly variable so give no indication of the problem. The first signs may therefore be due to physical effects on the surrounding structures such as straining and difficulty in passing faeces.

A large number of dogs with an anal sac tumour develop other clinical signs that are not readily explained by the local or wider spread of the tumour. This is known as a 'paraneoplastic syndrome'. There is abnormal parathyroid hormone production by the cancer that induces increased drinking, increased urine production, muscle weakness, slow heart beat and increased calcium levels in the blood. Kidney failure is possible.

How is the tumour diagnosed?

Clinically, this tumour can be difficult to diagnose but the site is one indicator of the possible type. Accurate diagnosis relies upon microscopic examination of tissue. Cytology (the microscopic examination of cell samples sucked from the tumour using a special needle) is sometimes helpful as a rapid or preliminary test. But histopathology (the microscopic examination of specially prepared and stained tissue sections made from actual pieces of the tumour) is needed for full diagnosis. This is done at a specialised laboratory where the slides are examined by a veterinary pathologist. The information from histopathology is more detailed than cytology and will better indicate how the cancer will behave (the prognosis) and whether the cancer has been fully removed.

What treatment is available?

Treatment is surgical removal of as much of the cancer as possible given that it tends to be so invasive of surrounding tissues.

Can this cancer disappear without treatment?

Essentially, the answer is No.

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 veterinarian.

You may be asked to check that your pet can pass urine and faeces or to give treatment to facilitate this. If you require additional advice on post-surgical care, please ask.

How will I know if the cancer is permanently cured?

'Cure' has to be a guarded term in dealing with any cancer.

Histopathology will give your veterinarian the information that will help to indicate how the tumour is likely to behave. The veterinary pathologist usually adds a prognosis that indicates the probability of local recurrence or metastasis (distant spread).

Theses are almost always malignant and may already have spread to regional lymph nodes and then various internal organs by the time the initial diagnosis is made. Even those that have not yet spread are usually not permanently cured. Another problem is hypercalcaemia (high blood calcium), which often persists which often leads to kidney failure.

The post-surgical survival range is two weeks to thirty-nine months (average eight months). Early detection and radical surgical removal of the lump and surrounding tissue gives a better prognosis but spread (metastasis) may have already occurred.

Are there any risks to my family or other pets?

No, this is not an infectious tumour and it is not transmitted from pet to pet or from pets to people.