Comprehensive Guide to Canine Anal Sac Cancer (Apocrine Gland Adenocarcinoma): Causes, Symptoms, and Treatment

ImmunityDiseasesMeongsiljang Veterinary Advisory Board

We’ve put together a comprehensive guide on apocrine gland adenocarcinoma, a malignant tumor that develops in a dog’s anal sacs, covering its causes, early symptoms, diagnosis, surgical and chemotherapy treatments, and recurrence management.

What Is Apocrine Gland Anal Sac Adenocarcinoma?

A veterinarian gently examining a puppy's anal gland area.

Apocrine gland anal sac adenocarcinoma is a malignant tumor that develops in the apocrine glands within the anal sacs, which are located on either side of a dog’s anus. Early detection is crucial. Although this cancer often shows no obvious external signs in its early stages, it tends to metastasize to nearby lymph nodes—particularly those in the pelvic cavity and below the lumbar vertebrae—and invade surrounding tissues. Therefore, if you notice a combination of abnormal defecation, a lump around the anus, and excessive thirst, do not delay; seek veterinary care promptly for diagnostic testing.

Causes and Pathogenesis

The exact cause remains unknown. Veterinary textbooks state that the etiology of apocrine gland adenocarcinoma of the anal sacs is "unclear." While it is reported more frequently in older female dogs, it can also occur in males. The disease primarily affects senior dogs, with most reported cases occurring around 10 to 11 years of age. Based on current textbook evidence, there is no clear indication that specific breeds are more susceptible or that spaying/neutering status is directly linked to the disease. Therefore, regardless of breed, it is crucial not to become complacent as your dog enters its senior years; regular, thorough veterinary check-ups are the most important preventive measure.

Key Symptoms Not to Miss

In the early stages, symptoms are often minimal, so the condition is frequently discovered incidentally during routine check-ups. However, if you notice any of the following signs, seek veterinary evaluation promptly.

Lump near the anus: One anal gland feels firm to the touch.

Abnormal defecation: Stools become ribbon-like or flattened, or your pet strains significantly during bowel movements.

Excessive licking of the anal area: Repeated licking or dragging of the rear end (scooting).

Excessive thirst and increased urination: Hypercalcemia can cause increased water intake.

Difficulty defecating and straining: Enlarged lymph nodes in the pelvic cavity or below the lumbar spine can lead to constipation and painful defecation.

Lethargy, vomiting, and loss of appetite: If hypercalcemia is present, your pet may appear weak, vomit, or show reduced interest in food.

A caregiver gently palpating and examining their dog’s body at home

Seek Veterinary Care Within 24 Hours If These Signs Appear

If any of the following signs are present, seek veterinary care immediately: 1) a firm lump is palpable near the anus; 2) the pet is drinking significantly more water than usual and experiencing a sudden increase in urine output (a warning sign of hypercalcemia); 3) lethargy accompanied by vomiting and loss of appetite; 4) excessive straining during defecation. Hypercalcemia, in particular, is an emergency because it can lead to acute kidney failure.

How Is It Diagnosed?

Diagnosis involves a step-by-step series of tests. First, a digital rectal exam is performed to assess the size and firmness of the anal sacs, followed by fine-needle aspiration (FNA) cytology to identify the type of tumor cells. A definitive diagnosis is established through histopathological examination, such as FNA cytology or excisional biopsy. Determining whether metastasis has occurred is the most critical step; this is evaluated using abdominal ultrasound, thoracic radiographs, and CT scans to examine the pelvic cavity and lymph nodes below the lumbar vertebrae. Blood tests must always include a check of calcium levels, as approximately 50–90% of dogs with apocrine gland adenocarcinoma present with concurrent hypercalcemia.

How Is Treatment Conducted?

The cornerstone of treatment is surgical excision. If the tumor is small and there is no evidence of metastasis, a wide surgical excision alone often yields a favorable prognosis. In cases of lymph node metastasis, the pelvic and caudal lumbar lymph nodes are also removed. If there is a risk of recurrence or metastasis after surgery, chemotherapy may be administered concurrently; reported chemotherapeutic agents include cisplatin, carboplatin, doxorubicin, and mitoxantrone. If hypercalcemia is present, intravenous fluid therapy is used to normalize calcium levels before proceeding with surgery.

The veterinary medical team preparing for surgery in the operating room of an animal hospital.

How to Care for Your Pet at Home?

Keep the Elizabethan collar on for 7 to 14 days after surgery to protect the incision. Feed a high-fiber, low-fat prescription diet to keep stools soft and minimize straining during defecation. Limit exercise to two or three short walks per day, and prohibit running or jumping for two weeks. Daily monitoring of water intake and urine output can help detect hypercalcemia recurrence early. Do not discontinue prescribed medications without veterinary guidance.

Regular Check-up Schedule for Recurrence Prevention

Apocrine gland adenocarcinoma has a high rate of recurrence and metastasis even after surgery. Regular check-ups are recommended every three months in the first year, and every six months from the second year onward. At each check-up, rectal palpation, abdominal ultrasound, chest X-rays, and blood calcium levels should be monitored. At home, it’s also helpful to gently palpate the area around the anus once a month.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Is anal sac cancer hereditary?

It is not a direct genetic disease. The exact cause of the disease has not been clearly identified even in textbooks, and it is difficult to confirm the evidence that certain breeds are more prone to it. However, since it mainly occurs in older dogs (around 10 years old), it is a good idea to check the area around the anus as they age and to have more thorough regular check-ups.

Will surgery cure the condition?

If the tumor is small and hasn’t spread, surgery alone can lead to long-term survival. However, if it has already spread to the lymph nodes, even with surgery and chemotherapy, there’s a risk of recurrence, so lifelong monitoring is necessary.

How is it different from perianal gland inflammation?

Anal sacculitis is an inflammatory condition that typically improves with anal sac expression and flushing, along with antibiotics and anti-inflammatory medications. In contrast, apocrine gland adenocarcinoma is a malignant tumor that cannot be treated with medication alone; surgical excision is the treatment of choice. If a lump feels firm and does not decrease in size despite medication, a cytology test is essential.

Why is hypercalcemia dangerous?

Elevated blood calcium levels can strain the kidneys, potentially leading to irreversible kidney damage. If your pet exhibits excessive thirst, vomiting, or lethargy, seek veterinary care immediately. Treatment typically begins with intravenous fluid therapy to stabilize calcium levels before proceeding with surgery.

Will expressing the anal glands in advance help prevent problems?

Regularly expressing the anal glands can help manage gland impaction and anal gland inflammation, but it does not prevent apocrine gland adenocarcinoma. However, a secondary benefit is that lumps may be detected earlier during routine expression.

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References

[1] Kudnig S.T., Séguin B., Veterinary Surgical Oncology, 2nd Edition, Chapter: Alimentary Tract - Perianal and Anal Sac Tumors, Wiley-Blackwell, 2022

[2] Thrall D.E., The Veterinary Workbook of Small Animal Clinical Cases, Case 26: Perianal Masses, Wiley-Blackwell, 2018

[3] Withrow S.J., Vail D.M., Page R.L., Small Animal Clinical Oncology, 6th Edition, Chapter: Tumors of the Gastrointestinal Tract, Elsevier, 2019

[4] Heaton C.M., Fernandes A.F.A., Jark P.C., et al., Evaluation of toceranib for treatment of apocrine gland anal sac adenocarcinoma in dogs, J Vet Intern Med 34(2):873-881, 2020