Pet Health Library

Background

Dogs have two anal glands (sacs), one on either side of the anus. While it isn’t common, a tumor of the anal sac can form in one or, rarely, both glands. Biopsy may show the tumor is an anal gland adenocarcinoma (AGASACA), anal sac carcinoma, or an apocrine gland carcinoma. All of these tumors have the same prognosis and are treated with the same therapy. These tumors have the potential to spread to other body parts, especially the lymph nodes, liver, and lungs. In addition, this cancer can elevate the calcium in the dog’s body, which can eventually lead to kidney damage.

Signs

Your dog may not exhibit any clinical signs or may show some or all of the following:

• Problems defecating
• A change in the stool shape
• Increased thirst or urination
• Issues with the anal sacs such as licking the area, swelling, or redness
• Lethargy, weight loss, decreased appetite
• Discomfort in the rear end or in the spine and hind legs

Diagnosis

It is important a thorough evaluation is performed to ensure that all the tumor is identified and can be treated. The evaluation will include blood work, chest x-rays, an abdominal ultrasound, and a biopsy or aspiration cytology of the anal mass and any abnormalities (such as sampling of the lymph nodes). A CT scan may be recommended.

Treatment

Surgery is often the mainstay of treatment. This is frequently combined with chemotherapy.

Radiation can be used for anal gland tumors in place of surgery, for tumors that are too large to remove, or following surgery if surgery cannot completely remove all tumor cells in the area. Radiation can also target internal lymph nodes if the tumor has spread to this region. Concurrent chemotherapy may be recommended.

Radiation therapy can be performed in 3, 6, 10, or 18 treatments, depending on the amount of cancer present, any other present medical conditions, and the goals of therapy. Treatment is typically given 3-5 times per week though at times it can be done once a week for 6 weeks. For each treatment, your pet will need to be anesthetized to ensure the utmost accuracy of treating the tumor site.

Radiation Side Effects
It is the goal of the radiation therapy team to minimize the side effects as much as possible. Unfortunately, there is always a risk of side effects with any medical treatment. Side effects occur only in the area that is receiving radiation.

• Acute Effects – these typically occur within the first few weeks of treatment up to a few weeks after radiation has been completed. Signs can include redness and soreness of the anal region, straining to defecate due to inflammation and irritation, pink/red or moist skin, and diarrhea (if the intestines receive radiation). Acute side effects typically resolve within weeks after radiation has been completed.
• Late Effects – these can occur months to years after radiation and though uncommon, can include narrowing and scarring of the anal sphincter and/or intestine, no fur in the RT area, white fur regrowth, skin discoloration, and dry/thin skin. While many patients will experience changes to their fur, they rarely will experience other late effects.

Every attempt will be taken to minimize side effects. Should they occur, your radiation oncologist will prescribe medications and possibly a diet change to help.

Prognosis

Prognosis will depend on the extent of the tumor, the goal of radiation therapy, and the presence of other diseases. Some dogs only do well for months, others can do week for a couple of years.