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If your dog has ever scooted their rear end across your carpet, they were probably trying to empty their anal sacs. Humans don’t have anal sacs that are similar to our pets, but dogs and cats, along with many other animals do.  A few pets may develop issues with these sacs, so, what are they?

Anal sacs, also called anal glands, are small balloon-like structures filled with a brown liquid known for its repulsively metallic, fishy smell. Dogs have two anal glands that sit just inside their anus at the 4 and 8 o’clock positions. When the dog defecates, some of the stinky fluid in these sacs is squeezed out with the feces. This liquid may play a role in territorial marking and communication among dogs.

What Are Anal Sac Tumors?

Many problems can affect a dog’s anal sacs, including tumors. Some cancerous anal sac tumors, known as Anal sac adenocarcinomas or apocrine gland anal sac adenocarcinomas are abnormal, malignant growths of the anal sac. They are uncommon but serious and can affect any dog but older dogs. Certain breeds such as Spaniels, German Shepherds, and dachshunds are at higher risk.

There are also benign forms of anal sac tumors (not malignant) called perianal gland adenomas.

Overall, anal sac tumors can bring illness, discomfort, and a decreased quality of life to your dog. Thus, it is essential to catch these tumors early, determine what type of tumor they are, and treat them as soon as possible.

What Causes Anal Sac Tumors?

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

Although we can’t pinpoint a cause, we do have some understanding of what’s happening at a microscopic level. Cells in the anal sac start dividing and multiplying in an uncontrolled manner. This cell division creates a mass that makes the anal sac larger, but this alone usually doesn’t cause issues, at least until the mass gets quite large.

The larger concern (with adenocarcinomas) is when cancer cells break away and travel to other parts of the body to make new tumors.  These malignant cells often spread to lymph nodes, which are small lumps of immune tissue scattered throughout the body. They can also spread to essential organs, such as the lungs, liver, and kidneys.

Another problem with anal sac tumors is that they sometimes increase the amount of calcium in the blood. High calcium levels can damage the kidneys, which are the organs that filter blood and make urine. High calcium levels can also disrupt the function of the nervous system, intestines, and heart. 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 if and to 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 stools and some swelling in the back legs. If 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:

• Swelling at the rear end
• Licking the rear end more than usual
• Bleeding around the anus
• Bloody stool

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. If they feel or see a growth, they might do a fine needle aspiration of the mass. This means they will poke the mass with a needle, suck out some of the cells, put them on a glass slide, and send it to a lab for evaluation. This information will help narrow down what the mass is. If these results are suspicious of cancer, your veterinarian will likely surgically remove 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 may do blood and urine tests, to check for high blood calcium and kidney damage, as well as 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. They may also refer you to a veterinary surgeon more well-versed in treating these serious tumors.

Surgery

If it is possible, surgical removal of the mass and any enlarged lymph nodes in the area is the main way to treat anal gland adenocarcinomas (malignant). Surgery has been shown to lengthen the survival time of dogs with anal sac adenocarcinomas. However, tumors may eventually reappear if cancer cells are left behind and the cancer cells may have already spread to other sites at the time of removal.

With perianal gland adenomas (benign), surgery usually cures the disease, but regrowth can occur in some dogs over time.

After surgery, some dogs won’t be able to control their bowel movements for a while and there is an infection risk at the surgical site, especially it is near the route feces take out of the body.

Chemotherapy and Radiation

Because anal sac tumors have such a high risk of spread, chemotherapy is often recommended after surgery. It involves giving medications, often via the mouth or blood, to kill or inhibit cancer cells throughout the body.

Radiation therapy may also be recommended after or instead of surgery if surgery isn’t possible. It involves using radiation to destroy cancer cells. It is only offered at certain facilities, such as veterinary schools and some specialty practices, due to the expense of the equipment. Some people travel significant distances to get radiation services.

Both chemotherapy and radiation therapy can have serious side effects that your veterinarian will discuss with you.

What is the Prognosis (Outlook)?

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 the prognosis depends on many factors such as: 

• The size of the tumor
• Spread throughout the body
• Blood calcium levels
• Type of treatment

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. Sometimes anal sac tumors are an incidental finding during a seemingly healthy pet’s physical exam. Maintaining a regular exam schedule as recommended by your veterinarian can help screen for anal sac and other abnormalities, hopefully keeping your dog as healthy and happy as possible.