Anal Gland Tumors In Dogs

Updated: May 2026

Dogs have two anal sacs, one on either side of the anus. These small, pouch-like sacs are located between the external and internal anal sphincter muscles and are lined with glands that produce a smelly, brownish-gray fluid. When a dog defecates, a small amount of this fluid is released. It is believed that this fluid is one of the ways dogs mark their territory.

Although anal gland tumors in dogs are not common, they can be serious. These tumors form in or near the anal sacs and are often aggressive. They may grow quickly, invade nearby tissue, or spread to lymph nodes or other areas of the body.

Canine anal gland tumors have several names, including anal sac adenocarcinoma, apocrine gland anal sac adenocarcinoma, AGASACA, anal gland carcinoma, anal gland adenocarcinoma, and anal sac carcinoma. These terms generally refer to the same type of cancer.

The symptoms of anal sac tumors in dogs may or may not be noticeable. You might see swelling or a growth in the perianal area. You might also notice your dog straining while trying to defecate, changes in stool shape, licking near the rectum, or increased thirst and urination. However, it is also possible that a tumor will not be found until a routine rectal examination performed by your veterinarian.

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Types Of Anal Gland Cancer In Dogs

Cancer of the anal sacs (also known as canine anal gland (or sac) adenocarcinoma or apocrine gland adenocarcinoma) is the most common malignant tumor found in a canine’s perianal region. Anal gland cancer, in fact, represents approximately 16.5%¹ of all malignant rectal tumors in dogs. These tumors typically occur in only one anal sac, but, on occasion, both sides may be affected.

Anal gland tumors tend to metastasize early and spread to surrounding body parts. Regional lymph nodes and the liver are most commonly affected, but anal gland tumors in dogs can also spread to the lungs. In addition, one of the side effects of anal gland adenocarcinoma in dogs is high blood calcium, which can damage the kidneys.

Some reports state that female dogs may be more likely to develop anal sac tumors, while other reports have concluded that both sexes are equally prone to developing this type of cancer. While anal sac tumors can occur in any breed, Cockers, Springers, German Shepherds, and Cavalier King Charles Spaniels may be at a higher risk of developing this type of cancer. Age is a clear factor, as these tumors are more likely to occur in older canines.

Signs & Symptoms Of Anal Gland Tumors In Dogs

Your canine may not exhibit any noticeable symptoms of anal gland cancer. However, the following are some of the typical signs and symptoms for which to watch:

• Problems with defecating: Including constipation, straining and painful bowel movements
• Changes in your dog’s stool: Stool may be flatter, thinner or appear ribbon-like
• Increased urination and thirst: You may notice your dog drinking and urinating more frequently due to increased calcium² levels caused by an anal sac tumor
• Issues with the anal sacs: Your dog may spend a lot of time licking this area, or you might notice a swelling or a growth in the perianal region. 

Diagnosis & Staging 

• Digital palpation: A thorough digital rectal examination of your canine can help your veterinarian or oncologist learn the size and extent of the tumor
• Aspiration cytology: A fine needle is inserted into the mass and the cells are examined to rule out other possible issues, such as infections or inflammation
• Biopsy: A biopsy is performed after the mass is removed to determine if it is malignant and to confirm the diagnosis
• Blood and urinalysis: These tests are performed to get a general assessment of your dog’s health and organ function and to check for infections, signs of disease, and other issues
• Three-view chest radiographs and abdominal ultrasound: These imaging studies are performed to determine whether the cancer has spread to other organs or to the lymph nodes

Treatment Options For Anal Gland Cancer

If the anal gland cancer has not spread, your veterinarian has several treatment options.

Surgery

A local treatment for anal sac tumors in dogs is surgery³. If the cancer has spread to other areas, such as the lymph nodes, those may also be removed.

Surgery With Chemotherapy

Chemotherapy may also be recommended after surgical excision if there is evidence that the cancer has spread.

Stereotactic Radiation Therapy (Concurrent With Chemotherapy)

PetCure Oncology’s stereotactic radiation therapy (SRT/SRS) delivers high doses of radiation with extreme precision to the cancerous tumor. In doing this form of radiation therapy, no surgery is needed. SRT/SRS results in less damage to the healthy tissue surrounding the tumor compared to other forms of RT. Recovery time with SRT is also fast, with few to no side effects.

Update: Stereotactic radiation (SRS/SRT) can now be delivered safely and effectively to cancer patients who have undergone surgery to remove a tumor but are still found to have residual cancer. This advancement was tested through a PetCure clinical trial conducted between May 2017 and March 2019, with findings published in the July 2023 edition of JAVMA, providing new hope for many dogs and cats that are in need of additional cancer care after undergoing tumor-removal surgery. This cutting-edge technology allows for the insertion of a liquid fiducial marker at the tumor site, either during or after surgery, providing a necessary target for planning radiation therapy. This innovative approach offers new hope for our furry companions in their fight against cancers like soft tissue sarcoma, mast cell tumors, and adenocarcinoma, like those found in anal sac adenocarcinoma.

If the cancer has spread: 

Your veterinarian may try to treat your dog with a combination of RT/chemo and possibly surgery. The prognosis with this treatment is still unknown.

If the mass is not treated, the tumor will grow larger, which will make it increasingly more difficult for your dog to push feces through his or her anus. If your dog is not a candidate for surgery, veterinarians recommend feeding your dog stool softeners and soft food, which should make it easier for him or her to have a bowel movement.

Life Expectancy, Survival & Prognosis

When it comes to anal gland cancer in dogs, life expectancy depends on several factors, including the type of treatment your pet receives:

• After surgery, if the margins of the tumor are not clean: The cancer often returns in six months
• After surgery and chemotherapy: Life expectancy is about 18 months
• After SRT, concurrent with chemotherapy: Life expectancy is about 18 months to two years
• Without treatment: Life expectancy is typically measured in months. Quality of life issues should be discussed.

Other factors can affect your dog’s life expectancy. For example, a dog with lung metastasis or high calcium levels will typically have a shorter life span.

Still have questions? Here are a few common questions families ask after a diagnosis.

Common Questions About Anal Gland Tumors in Dogs

Are anal gland tumors usually cancer?

They can be. One of the more concerning types is anal sac adenocarcinoma, also called AGASACA. This cancer can grow into nearby tissue and may spread, so veterinarians take it seriously when they find it.

What symptoms might I notice at home?

Some dogs strain to defecate and have stool that looks thinner than usual, they may scoot, lick near the rectum, or develop swelling near the anus. Some also drink or urinate more than normal. Other dogs do not show much at all, which is why these tumors are sometimes found during a rectal exam.

What treatment options are available?

Treatment depends on what is found during the exam and staging tests. A variety of treatment options may be offered for dogs with anal sac cancer including surgery, radiation therapy, chemotherapy, or a combination of those treatments. The goal may be to control the tumor, help keep your dog comfortable, or both.

What does this diagnosis mean for my dog?

It depends on the tumor, whether it has spread, and how your dog is feeling overall. Your veterinarian or veterinary oncologist can talk through what is realistic for your canine companion and help you understand the options.

For more information on anal sac tumors or treatment, please contact your local PetCure Oncology Center. We have understanding and caring team members who are ready to answer your questions.

RELATED: Information Sheet: Anal Sac Adenocarcinoma