Anal Sac Tumors in Dogs and Cats

Although cancer can occur in many parts of the body, one type we see often is anal sac tumors. The anal sacs are small glands located adjacent to the rectum in dogs and cats. The sacs produce an odorous liquid that is typically expressed during bowel movements. However, the sacs may become obstructed, infected, or develop tumors within.

Signs of Anal Sac Tumors

The clinical signs associated with anal sac tumors may include excessive licking of the area, scooting, or bleeding/discharge from the sac. You may also notice a tumor due to a large swelling around the rectum. The size of this tumor may also lead to difficulty defecating or smaller, thinner, ribbon-like stools. Dogs may develop excessive thirst and urination secondary to elevated calcium with an anal gland tumor. Your veterinarian will perform a physical exam to determine the cause of these sign. If a tumor is noted, it indicates the need for further testing.

Diagnosing Your Pet

The primary diagnostic test is a fine needle aspirate (FNA). This is a safe procedure but may require a light sedative for your pet’s comfort. During the procedure, a small needle is used to remove a sample of cells from the tumor. If an anal sac tumor is confirmed, your veterinarian may recommend additional testing. This is because unfortunately, anal sac tumors have a high likelihood of metastasis, meaning the cancer spreads to other areas.

The most common location for metastasis is within the lymph nodes which may be located within the pelvis or abdomen. The specific staging tests for anal sac tumors will include lab work, X-rays, abdominal ultrasound, and/or CT (CAT) scan. The lab work will not provide specific information regarding the diagnosis or stage of the cancer but will be useful in assessing your pet’s overall health and in identifying whether calcium levels are affected. Collectively, this informs our treatment recommendations and overall prognosis.

Treating Anal Sac Tumors

The primary treatment recommendation for anal sac tumors is surgery. Surgery may include removal of the primary tumor and/or removal of metastatic lymph nodes. This may be a staged procedure or completed all at once. If surgery is not an option, radiation therapy may be considered, and your pet’s oncologist will discuss the specific radiation protocol depending on the goals of treatment.

In addition, chemotherapy may be included as part of the treatment regimen after surgery or radiation. If surgery or radiation is not recommended or pursued, your veterinarian may recommend an oral chemotherapy called Palladia (toceranib). This has been shown to improve clinical signs secondary to anal sac tumors and extend the prognosis in pets that are unable to go through the primary treatment recommendations.

The Prognosis for Your Pet

The prognosis for dogs with anal sac tumors depends on the size of the tumor, presence of metastasis, and treatment pursued. Your MedVet oncology team will work together with you and your family veterinarian to provide the best treatment recommendations to facilitate the highest quality of life while aiding in extending your pet’s life despite their cancer diagnosis.