If your dog has ever scooted their rear end across your carpet, they were probably trying to empty their anal sacs. Anal glands (or sacs) are just that, glands located just inside the rectum and secrete fluid. Sometimes the glands get clogged and fill up with fluid causing your dog to scoot.

To be more specific, think of the glands as small balloons (see image below) filled with a brown liquid notorious for its repulsively metallic, fishy smell. Dogs have two anal glands that sit just inside their anus at the 4-5 and 7-8 o’clock positions. When the dog defecates, normally fluid in these sacs is squeezed out with the feces. This liquid may play a role in territorial marking and communication amongst dogs.

dog with anal gland tumors

Besides the glands getting clogged, other problems can affect a dog’s anal sacs, including tumors. Anal sac tumors are abnormal cancerous growths in the anal sac. They are uncommon but serious and left untreated are generally fatal. They can affect any dog but older dogs and certain breeds such as spaniels, German Shepherds, and dachshunds are at higher risk.

These tumors cause problems as they spread locally and to distant sites of the body in a process called metastasis. They can bring illness, discomfort and a decreased quality of life to your dog. Thus, it is essential to catch these tumors early and to treat them as soon as possible.

What causes anal sac tumors?

anal gland tumors on a dog

As with most cancers, a cause has not been identified. However, genetics and environmental factors probably play important roles.

Besides spreading to other organs, anal gland tumors can press on the rectum and make defecating difficult. Some of these tumors can also affect the absorption and metabolism of calcium leading to elevations in calcium. 

High calcium levels can damage the kidneys, change muscle function and the heart’s ability to contract normally. As you might imagine, this disruption can cause a range of symptoms and issues for your dog.

What are the signs of anal sac tumors?

It depends on the behavior of the tumor and where it has spread. Many dogs won’t show any signs. However, when the tumor spreads to nearby lymph nodes or the mass gets large, your dog may strain and struggle to defecate, or not even defecate at all.

They can also have ribbon-like stool and swollen back legs. When the tumor increases blood calcium levels, your dog may drink and pee more, eat less, vomit and seem weak and tired.

Other possible signs include:

Dogs with anal sac tumors may also scoot, meaning they sit and drag their rear end against the ground. However, scooting much more commonly indicates full or inflamed anal glands that need to be expressed (squeezed) by your veterinarian, rather than cancer.

How are anal sac tumors diagnosed?

Your veterinarian will talk to you about the history of your dog’s problem as well as perform a physical exam. As part of this, they may conduct a rectal exam to feel for the tumor.

During this procedure, they will stick a gloved finger through your dog’s anus into the rectum, which is the tube carrying feces out of the body. If they feel or see a growth, they might do a fine needle aspiration of the mass and send it to a lab to confirm it is cancer.

Your veterinarian will also do additional tests to figure out if and where the tumor has spread and if it has affected the body in other ways. For example, your veterinarian will do blood and urine tests to check for high blood calcium and kidney damage. They will also do chest x-rays and abdominal ultrasound to see if the tumor has spread to the lymph nodes and organs, such as the lungs, liver and kidneys.

How are anal sac tumors treated?

Until more serious treatment can be pursued, your veterinarian may recommend stool softeners to make it easier for your dog to defecate and give fluids and medications to lower blood calcium.

They may also refer you to a veterinary surgeon for removing these tumors. If it is possible, treatment generally involves surgical removal of the mass and any enlarged lymph nodes in the area. This may need to be combined with radiation and chemotherapy. 

What is the prognosis?

Survival times for dogs with anal sac tumors are variable but on average range from about 1-2 years. However, every dog’s situation is different because prognosis depends on many factors such as: 

Dogs who receive surgery or any type of treatment generally have a better prognosis whereas the outlook is often less promising for dogs with larger tumors, high blood calcium levels, and extensive spread of the tumor.

How can I prevent anal sac tumors?

There’s no proven way to prevent anal sac tumors from developing. Early detection is important and may be achieved through routine rectal exams performed by your veterinarian. In fact, sometimes anal sac tumors are an incidental finding during a seemingly healthy pet’s physical exam.

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