Anal gland cancer in dogs (apocrine gland anal sac adenocarcinoma) is a malignant tumor of one of the two small scent sacs beside the anus. It makes up about 2% of skin tumors and usually affects dogs around 10 years old.1,2,3 It is easy to miss at home: many dogs have no signs at first, and the tumor is often found only on a rectal exam, so ask for one at senior checkups.2,4,5 About 1 in 4 affected dogs has high blood calcium, which causes thirst and frequent urination.1,6,4 About half have already spread to lymph nodes inside the belly, even when the tumor is small.1,7,6 Surgery is the main treatment, and many dogs live 1.5 to 3 years afterward.8,1 For other anal sac problems, see anal gland problems in dogs.
See your vet promptly if your dog has:
- A lump or swelling beside the anus1,9
- Straining, constipation or thin, ribbon-like stools9,1
- Increased thirst and urination, vomiting, poor appetite or tiredness, which can be signs of high calcium1,2
- Scooting or licking that keeps coming back, especially in an older dog9,10
Severe high calcium is an emergency, so a dog that is very weak or vomiting repeatedly needs care the same day.11,1
What the Research Says
- Even small tumors spread. In 116 dogs, 20% of tumors under 2 cm had spread to lymph nodes, compared with 63% of larger tumors.7
- Early tumors do very well with surgery. In 34 dogs with small tumors and no spread, median survival after surgery alone was 1,237 days (over 3 years).11
- Treatment still helps after spread. In a 2021 UK study of 81 dogs, dogs with spread that had surgery or radiation lived far longer than those given no treatment or medicines alone.6
- Radiation may beat surgery for very large nodes. In a European study of 28 dogs with very large lymph nodes (stage 3b), radiation gave a median survival of 447 days compared with 182 days after surgery.11,4
What Are the Anal Glands?
The anal sacs are two small pouches on each side of the anus, lined with glands that make a foul-smelling secretion. They are related to a skunk's scent glands, and the secretion is normally squeezed out when your dog passes stool.12,9 Most anal sac problems, such as impaction and infection, are not cancer, but the signs can overlap, which is why a rectal exam matters.9,13
Signs of Anal Gland Cancer
Between 20% and 57% of dogs have no signs when the tumor is found.5 The tumor itself is "usually nonpainful," and the main growth can be too small to feel even when the lymph nodes inside the pelvis are very large.13,11 When signs appear, they include:
- A swelling beside the anus, scooting or licking9,10
- Straining, constipation, ribbon-like stools or blood in the stool, often because enlarged lymph nodes press on the bowel1,9,11
- Thirst, frequent urination, weakness, vomiting and poor appetite from high calcium1,2
- Hind leg weakness or swelling if the lymph nodes are very large2
High calcium
The tumor can make a hormone-like protein that raises blood calcium.11,14 Estimates range widely, but about 1 in 4 dogs is affected.1,6,5 High calcium can damage the kidneys, and severe high calcium is an emergency. It is treated with fluids and other medicines, and it usually falls after the tumor is removed.1,11,10 See why is my dog drinking so much water.
Benign Perianal Adenoma vs Anal Sac Cancer
| Perianal adenoma | Anal sac cancer | |
|---|---|---|
| Where it grows | Skin glands around the anus, tail base or prepuce15 | Inside the anal sac, beside the anus1,9 |
| Who gets it | Mostly older unneutered males15,12 | Males and females at about the same rate, usually neutered or spayed1,13,10 |
| Behavior | Benign and slow-growing15 | Malignant; often spreads to lymph nodes1,11 |
| Treatment | Neutering plus removal; small ones often shrink after neutering15,12 | Surgery, sometimes with radiation1,8 |
High calcium points toward anal sac cancer rather than a perianal gland tumor. A needle sample or biopsy tells them apart.1,9
Which Dogs Get It?
Spaniels are at higher risk. English Cocker Spaniels were about 7 times more likely to be affected in a UK study, and English Springer Spaniels, Cavalier King Charles Spaniels, German Shepherds, Dachshunds, Alaskan Malamutes and Golden Retrievers are also listed.16,2,3 Most studies find no strong difference between male and female dogs, though two recent reports found about two-thirds were male, and the tumor doesn't seem to depend on hormones.11,13,1
Diagnosis and Staging
- Rectal exam: your vet feels the anal sacs and the lymph nodes inside the pelvis.11,1
- Needle sample or biopsy of the lump confirms the diagnosis.1,9
- Blood tests check calcium and kidney function.1,8
- Abdominal ultrasound and chest X-rays look for spread. CT is better at finding lymph nodes hidden by the pelvic bones.8,11,14
Tumors are staged by the size of the main tumor (about 2.5 cm is the cutoff), the size of any affected lymph nodes and whether the cancer has spread further. This system comes from a UK study.14,11 Newer lymph node mapping with CT is being studied in the US to find hidden spread.17
Treatment
Surgery
Removing the anal sac tumor is the main treatment.1,11 When lymph nodes inside the belly are enlarged, removing them through a separate belly incision is usually recommended and is linked to longer survival in most studies. It is a bigger operation with risks of bleeding and nerve injury, so it is often done by a specialist surgeon.14,2,11 Dogs with high calcium may need fluids before surgery.1
Some dogs leak stool for a while afterward, especially after removal of a large tumor. It is usually temporary and partial.1,11 Complications occur in roughly 1 in 10 dogs.11,2,3
Radiation
Radiation can be given before or after surgery, or instead of surgery when the tumor or nodes can't be removed safely.11,18 In one study of dogs with advanced disease, 63% of dogs with signs saw them improve or resolve.11 Side effects can include inflammation of the rectum and, later, narrowing of the rectum or incontinence.11,10
Medicines
Chemotherapy or a targeted kinase-inhibitor tablet may slow the disease or shrink tumors that can't be removed, but neither has been proven to lengthen life after surgery.8,11,19 Comfort care can include NSAID-class pain relievers, a stool softener and avoiding high-fiber diets.2,9 See dog cancer treatment for side effects and approximate costs.
Life Expectancy
| Situation | Typical median survival |
|---|---|
| Small tumor, no spread, surgery | About 3 years or more; some dogs are cured11,8 |
| All dogs, across studies (most had surgery) | About 1 to 2.5 years (386 to 960 days, from a UK review)14,3,6 |
| Spread to lymph nodes, surgery with or without chemotherapy | About 1 to 2 years (404 to 713 days)11 |
| Spread to lungs or other organs | Usually under 1 year8,3 |
Larger tumors and spread beyond the lymph nodes predict shorter survival. High calcium has been linked to shorter survival in several studies, though not all.11,3,6 The tumor can regrow, so regular rechecks are important.2,11 Your vet or oncologist can estimate your dog's outlook.
Frequently Asked Questions
What are the first signs of anal gland cancer in dogs?
Often none. When signs appear, they include a lump beside the anus, straining, ribbon-like stools, and thirst from high calcium.
Is anal gland cancer in dogs painful?
The tumor itself is usually not painful, but constipation and straining can be uncomfortable.
Is anal gland cancer the same as an impacted anal gland?
No. Impaction and infection are common and aren't cancer, but the signs can look alike. A sac that is firm, enlarged and can't be emptied should be checked for a tumor.
How long can a dog live with anal gland cancer?
After surgery, many dogs live 1.5 to 3 years, and some are cured. Dogs with widespread disease usually live less than a year.
Can anal gland cancer be prevented?
There is no known prevention. A rectal exam at each senior checkup is the best way to find it early.
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Sources and further reading
This article was rewritten and fact-checked on October 29, 2026 against current veterinary references and specialist guidelines:
- American College of Veterinary Surgeons. Anal sac tumors in dogs, June 2025.
- Cornell Richard P. Riney Canine Health Center. Anal sac adenocarcinoma. Cornell University College of Veterinary Medicine, undated (accessed October 2026).
- Veterinary Society of Surgical Oncology. Anal sac tumors.
- Mehler SJ. Anal sac anal gland adenocarcinoma: how combination therapy impacts outcome. IVC Journal, October 9, 2019.
- Cino M, Martano M. Is there anything new in canine apocrine gland anal sac adenocarcinoma? Veterinary Sciences, 2024.
- Wong H, Byrne S, Rasotto R, Drees R, Taylor A, Priestnall SL, Leo C. A retrospective study of clinical and histopathological features of 81 cases of canine apocrine gland adenocarcinoma of the anal sac: independent clinical and histopathological risk factors associated with outcome. Animals 2021;11(11):3327.
- Jones AE, Wustefeld-Janssens BG. Frequency of metastasis by tumor size in dogs with apocrine gland anal sac adenocarcinoma. Veterinary and Comparative Oncology, 2023. Summarized in Clinician's Brief.
- American Animal Hospital Association. Table 1.1: Common cancers of dogs. 2026 AAHA Oncology Guidelines for Dogs and Cats, 2026.
- Barnes C, Weir M, Pinard C. Anal sac tumors. VCA Animal Hospitals, updated May 26, 2025.
- Gauthier M, Barber LG, Burgess KE. Identifying and treating anal sac adenocarcinoma in dogs. dvm360, February 1, 2009.
- Findji L. Anal sac adenocarcinomas: what we have learned in the last 15 years. ECVS Annual Scientific Meeting, 2019. Conference proceedings hosted by IVIS (full text requires free IVIS login).
- Rubin SI. Disorders of the rectum and anus in dogs. Merck Veterinary Manual (pet owner version), September 2024.
- Gallagher A. Anal sac disease in dogs and cats. Merck Veterinary Manual, August 2025.
- (Author not shown on fetched page.) Diagnosis and management of canine anal sac adenocarcinomas. Veterinary Practice (UK), undated (accessed October 2026).
- Weir M, Stoewen D. Hepatoid Gland Tumors. VCA Animal Hospitals, updated March 2025.
- Science for Animal Welfare (UFAW). Cocker Spaniel: anal sac adenocarcinoma. April 2026.
- Griffin MA, Flesner BK, Worley DR, Holt DE, Gill N, Ghanian A, Talone M, Reetz J. Incorporation of pre- and intra-operative sentinel lymph node mapping techniques in dogs with apocrine gland anal sac adenocarcinoma. Veterinary Oncology 2024;1:5.
- American Animal Hospital Association. Table 5.6: Considerations for radiation therapy and treatment goals. 2026 AAHA Oncology Guidelines for Dogs and Cats, 2026.
- Heaton CM, Fernandes AFA, Jark PC, Pan X. Evaluation of [a kinase-inhibitor drug] for treatment of apocrine gland anal sac adenocarcinoma in dogs. Journal of Veterinary Internal Medicine 2020;34(2):873-881.
About this article
Last updated : new page written using the 2026 AAHA Oncology Guidelines, the American College of Veterinary Surgeons, Cornell University, the Merck Veterinary Manual, the Veterinary Society of Surgical Oncology, studies published 2020 to 2024 and IVIS-hosted proceedings; includes the research summary, signs, high calcium, adenoma comparison, staging, treatment, life expectancy table, key takeaways and FAQ.
This page is for general information and is not a substitute for an exam by your veterinarian.
