Anal Gland Tumors

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”. Your veterinarian may suggest certain tests to help confirm or eliminate 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 for tumors in animals is improving all the time.

We understand that this can be a very worrying time. If you have any questions please do not hesitate to ask us.

What are the anal glands and anal sacs?

Dogs and cats have a pair of anal sacs, one located on each side of the anus between the external and internal anal sphincter muscles. The sacs are lined with modified sweat glands called anal glands. The anal glands normally produce foul-smelling, grey-brown, granular secretions, which are stored in the anal sacs.

What is an anal gland tumor?

This tumor is a disordered and purposeless overgrowth of cells originating from the modified sweat glands of an anal sac. The tumor is usually rapidly growing, almost always malignant (spreading), and extends deep into surrounding tissues. The malignant tumor (anal gland carcinoma) may also spread to other parts of the body (metastasize), but such metastasis is usually slow to occur.

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 the culmination of a series of circumstances that come together for the unfortunate individual. We do not know what causes an anal gland tumor.

Is this a common tumor?

“The malignant form of the tumor (carcinoma) is uncommon in dogs and rare in cats.”

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

How will this cancer affect my pet?

You may first notice this tumor as a lump beside the anus. Since growth is often inwards, the lump may not appear as large as the actual tumor. Anal sac size and the color and consistency of its secretions are highly variable, so give no indication of the problem. The first signs may be straining and difficulty in passing feces, caused by physical effects on the surrounding structures.

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

How is an anal gland tumor diagnosed?

Clinically, this tumor 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 drawn from the tumor using a needle and syringe) is sometimes helpful as a rapid or preliminary test. However, histopathology (the microscopic examination of specially prepared and stained tissue sections made from actual pieces of the tumor) is needed for an accurate diagnosis. Your veterinarian will send samples of the tumor tissue to a specialized laboratory, where a veterinary pathologist will perform a histopathology examination. The histopathology report will include information on the type and grade of tumor (the type of cells and their degree of resemblance to normal cells), how it is likely to behave (the prognosis) and whether, if the sample represented an excision biopsy, the cancer has been fully removed.

What treatment is available?

Local treatment is surgical removal of as much of the cancer as possible, given that it tends to be so invasive of surrounding tissues. However, surgery may need to be repeated. Drug treatment (chemotherapy) or radiation may also be considered in some situations as a means of slowing recurrence or spread of the cancer.

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 tumor will reduce itching, inflammation, ulceration, infection and bleeding. Any ulcerated area needs to be kept clean.

After surgery, you need to keep the operation site clean and dry and your pet should not be allowed to interfere with the site. Report any loss of sutures or significant swelling or bleeding to your veterinarian.

You may be asked to check that your pet can pass urine and feces 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?

‘Cured’ 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 tumor is likely to behave. The veterinary pathologist usually adds a prognosis that indicates the probability of local recurrence or metastasis (distant spread). Other diagnostic tests such as radiographs of the chest and abdomen, and/or ultrasound of the abdomen may help determine if the cancer has already spread.

“Anal gland tumors are almost always malignant and may already have spread.”

Anal gland tumors are almost always malignant and may already have spread to regional lymph nodes and then to various internal organs by the time of the initial diagnosis. Even if the tumor has spread at the time of diagnosis and surgery, a permanent cure is rare, and the tumor can recur. Another problem is hypercalcemia (high blood calcium), which is related to the abnormal hormone production and which often persists. Hypercalcemia may cause kidney failure as a possible sequel.

“hypercalcemia (high blood calcium) often persists.”

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 tumor and it is not transmitted from pet to pet or from pets to people.