Anal Gland Cancer in Dogs

If your dog is drinking and urinating far more than normal...

Marked increases in thirst and urination alongside an anal mass can indicate high blood calcium, which damages the kidneys if it persists. Add weakness, vomiting, or loss of appetite and this needs attention within days rather than weeks.

High calcium is treatable, and treating the tumor usually resolves it.

Anal Sac Adenocarcinoma

Dogs have two small scent glands, one on each side of the anus, which empty through tiny ducts. Anal sac adenocarcinoma arises from the tissue lining these glands.

Two features define how it behaves.

It spreads early to lymph nodes inside the abdomen. By the time it is diagnosed, a substantial proportion of dogs, commonly estimated at around half, already have involvement of the sublumbar lymph nodes deep in the pelvis. These nodes can grow large enough to press on the rectum and cause difficulty passing stool. Later spread reaches the liver, spleen, and lungs.

It frequently produces a hormone-like substance that raises blood calcium. Roughly a quarter to a half of affected dogs develop high calcium, which causes increased thirst and urination, weakness, reduced appetite, vomiting, and, if sustained, kidney damage. This is often what brings a dog to the veterinarian, sometimes before anyone has noticed a lump.

Which dogs are affected

Older dogs, typically around ten. Cocker Spaniels, English Cocker Spaniels, Springer Spaniels, Dachshunds, German Shepherds, and Alaskan Malamutes appear more often than average.

Both sexes are affected. Older reports suggested a strong female predisposition; more recent data indicate the sexes are affected in broadly similar numbers.

Signs to look for

Many of these tumors are found before any signs appear, during a routine rectal examination. That is worth knowing, because it is one of the few cancers in this library that regular examination genuinely catches early.

When signs do appear:

• A firm lump beside or below the anus, which may be small
• Scooting, licking, or biting at the rear
• Straining to defecate
• Ribbon-shaped or flattened stool
• Discomfort when defecating
• Swelling on one side of the anal area
• Blood or discharge from the anal area

From high blood calcium:

• Markedly increased thirst and urination
• Weakness and lethargy
• Reduced appetite
• Vomiting
• Muscle tremors in more severe cases

Scooting is worth taking seriously in an older dog. It is usually caused by ordinary anal gland problems, which are common and benign. But scooting that persists, or occurs in a dog who has not had gland trouble before, is a reason to ask for a rectal examination rather than assuming.

How it is diagnosed

Rectal examination is the key step and identifies most of these tumors. It takes seconds. If your dog has any of the signs above, this examination is what should happen.

Fine needle aspiration of the mass usually gives a diagnosis, as these tumors have a recognizable appearance on cytology.

Bloodwork including ionized calcium is essential. Total calcium on a standard panel can be misleading, so ionized calcium is the more accurate measure. Kidney values are checked at the same time, since sustained high calcium damages them.

Abdominal imaging: Ultrasound or, better, CT, assesses the sublumbar lymph nodes. This is not optional. These nodes sit deep in the pelvis, cannot be felt externally, and their status changes the treatment plan. CT is more accurate than ultrasound for this and is worth asking about.

Chest imaging checks for spread to the lungs.

Treatment

Surgery to remove the affected anal sac is the primary treatment. The tumor and the gland are removed together.

The main risk is damage to the nerves controlling the anal sphincter, which can result in fecal incontinence. In experienced hands this is uncommon, and it is a reason to have this surgery done by a surgeon who performs it regularly.

Removal of enlarged lymph nodes is frequently recommended alongside, and this matters more than families often expect. Removing involved sublumbar nodes relieves the pressure causing difficulty defecating and is associated with longer survival. It is a more demanding operation, performed deep in the abdomen.

Radiation is used for lymph nodes that cannot be removed, for incomplete margins, or to relieve symptoms. It achieves good local control.

Chemotherapy is commonly recommended given the high rate of spread. Carboplatin and mitoxantrone are among the agents used. Evidence that it extends survival is mixed rather than definitive, and it is fair to ask your oncologist what they expect from it in your dog's case.

Toceranib, a targeted oral drug, has activity against this tumor and is used particularly for disease that has spread or recurred. It is given as tablets at home.

Treating high calcium happens alongside and sometimes before cancer treatment. Intravenous fluids are the mainstay, with additional medications where needed. Removing the tumor usually normalizes calcium, and a calcium level that rises again afterward is often the first sign the disease has returned.

Outlook

These are medians across many dogs. Half lived less, half lived longer.

With surgery, and where appropriate radiation and chemotherapy, reported median survival commonly falls between roughly one and two years.

Dogs with small tumors, no lymph node involvement, and normal calcium do considerably better, some series report well over two years. Dogs with distant spread at diagnosis or persistently high calcium do less well.

Local recurrence is common, and the disease is generally controlled rather than eliminated. That said, this is a cancer where active treatment makes a substantial difference, and many dogs have a good year or more of normal life.

Perianal Tumors 

These arise from specialized glands in the skin around the anus, and they are a different situation entirely.

Perianal adenoma is benign and common. It occurs overwhelmingly in unneutered male dogs, because these glands are stimulated by testosterone. Tumors appear as one or more firm nodules around the anus, sometimes ulcerating.

Treatment is removal combined with neutering. Neutering removes the hormonal drive, and the combination usually resolves the problem permanently. Neutering alone sometimes causes existing tumors to shrink. Cocker Spaniels, Beagles, Samoyeds, and Siberian Huskies are affected more often.

Perianal adenocarcinoma is the malignant counterpart and is much less common. It is not hormone-dependent, occurs in both sexes and in neutered dogs, and can spread to lymph nodes. It requires wider surgical removal and staging.

The two cannot be distinguished by appearance. Any perianal mass should be examined and biopsied rather than assumed benign, particularly in a female or neutered dog, where the benign hormone-driven form is unlikely.

What treatment is actually like for your dog

Anal sac removal is generally well tolerated. Most dogs go home within a day or two. The area is uncomfortable for several days, and defecation is often difficult at first; stool softeners are commonly prescribed. Most dogs are comfortable within a week or two.

Some dogs experience temporary reduced control over defecation in the first days after surgery, which usually resolves. Permanent incontinence is uncommon but is the risk worth discussing with your surgeon beforehand.

Lymph node removal involves abdominal surgery, with two to three days in hospital typically and about two weeks of restricted activity.

Radiation to this area causes soreness and inflammation of the skin and rectal lining, which can make defecation uncomfortable for a period. This is managed with pain relief and stool softeners and settles over several weeks.

Chemotherapy for dogs is dosed for quality of life rather than for eliminating the disease at any cost. Most dogs experience no significant side effects and most do not lose their coat. 

Toceranib tablets are given at home with periodic bloodwork. Digestive upset is the most common side effect and dose adjustments are routine.

Integrative and supportive care

Stool consistency is the practical daily issue. Firm stool is painful to pass through a surgical site or an irritated rectum, and straining is uncomfortable and can affect healing. Ask your veterinary team about stool softeners and appropriate fiber, and follow their guidance rather than adjusting on your own, this is one area where getting it right matters day to day.

Keep the area clean and dry, and check it while it heals.

Where high calcium is present, adequate water intake matters considerably. Make sure fresh water is always available and easy to reach.

Be cautious with supplements. Anything affecting clotting is relevant around surgery, and products affecting the digestive tract can worsen stool problems. Tell your veterinary team about everything your dog receives.

No supplement, herb, or diet has been shown to treat anal sac adenocarcinoma. 

Comfort care alone

For an older dog with other serious conditions, or where disease is advanced, comfort-focused care centres on managing defecation, pain relief, and controlling calcium.

Calcium management matters particularly here, because high calcium makes dogs feel genuinely unwell: Thirsty, weak, nauseated, and treating it improves quality of life even when the tumor is not being treated. Ask your veterinarian about this specifically.

The complication to plan for is obstruction. Enlarged lymph nodes or a growing tumor can eventually make defecation very difficult. Discuss in advance what you would want to do if that develops.

What It Costs

Costs vary by region and practice type. Ask for a written estimate.

• Examination, aspiration, and bloodwork with ionized calcium: approximately $400 to $800
• Abdominal ultrasound: approximately $400 to $600
• CT for staging: approximately $1,500 to $3,000
• Anal sac removal: approximately $2,000 to $4,000
• Combined with lymph node removal: approximately $4,000 to $7,000
• Radiation: approximately $4,000 to $8,000
• Chemotherapy: approximately $2,000 to $5,000
• Toceranib: typically several hundred dollars per month
• Perianal adenoma removal with neutering: approximately $800 to $2,000

Living With It Day-to-Day

Watch defecation. Straining, ribbon-shaped stool, or difficulty passing stool can indicate enlarged lymph nodes and should be reported.

Watch water intake. A return of excessive thirst after treatment often signals rising calcium and may be the earliest indication the disease is active again. This is genuinely useful monitoring you can do at home.

Ask for regular rechecks including rectal examination and ionized calcium. Recurrence is common enough that scheduled monitoring matters, typically every two to three months at first, and it is usually caught on examination before it becomes obvious.

Report to your veterinary team: increased thirst or urination, straining or difficulty defecating, scooting or licking at the rear, a new lump in the area, reduced appetite, weakness, or vomiting.

Questions Worth Asking Your Oncologist

• Is this an anal sac tumor or a perianal tumor?
• What is my dog's ionized calcium, and are the kidneys affected?
• Have the sublumbar lymph nodes been assessed, and by ultrasound or CT?
• Should enlarged lymph nodes be removed, and what does that add?
• What is the risk of incontinence with this surgery, and how often do you perform it?
• What would chemotherapy or toceranib realistically add here?
• How often should we recheck, and will that include calcium?
• What should I watch for at home that would suggest it is returning?

Thinking About Quality of Life

The quality-of-life issues here are specific: comfort while defecating, and how high calcium makes a dog feel.

Both are treatable, which makes them worth raising promptly rather than accepting. A dog straining painfully to defecate, or one drinking constantly and feeling nauseated from high calcium, can often be made considerably more comfortable.

Track your dog weekly across a few consistent dimensions — comfort, appetite, energy, ease of defecating, thirst, engagement with the family, and whether good days still outnumber bad. Written notes over months are more reliable than memory.

Ask your veterinary team what the likely course looks like and what to expect if defecation becomes obstructed, so that decision can be considered in advance rather than in a crisis.

Common Questions

My dog has been scooting. Should I be worried? Usually it is ordinary anal gland trouble, which is common and benign. But scooting that persists, or begins in an older dog with no history of it, is a reason to ask for a rectal examination. That examination takes seconds and is how many of these tumors are found.

Why is my dog drinking so much? Anal sac adenocarcinoma frequently produces a substance that raises blood calcium, which causes marked thirst and urination. It is treatable, and removing the tumor usually normalizes it, but sustained high calcium damages the kidneys — so it warrants prompt attention.

Can anal gland cancer be eliminated for good? It is generally controlled rather than eliminated. Local recurrence is common. That said, with surgery and appropriate additional treatment, many dogs have a good year or more, and dogs with small tumors, clear lymph nodes, and normal calcium can do considerably better.

Will my dog be incontinent after surgery? Some temporary reduction in control is common in the first days. Permanent incontinence is uncommon when the surgery is performed by an experienced surgeon, and it is a fair question to ask about how often yours does this procedure.

Do the lymph nodes really need to come out? Where they are involved, removing them relieves pressure on the rectum and is associated with longer survival. It is a more demanding operation, so discuss with your surgeon whether it is appropriate for your dog.

My dog has a lump near the anus but is neutered and female. What could it be? Not the common benign perianal adenoma, which occurs almost exclusively in unneutered males. Any perianal mass in a female or neutered dog should be examined and biopsied rather than assumed benign.

How would this be caught earlier? By rectal examination, which is why it is worth including in senior wellness checks and worth requesting if your dog is scooting, straining, or drinking more than usual. Many of these tumors are found this way before any signs appear.

This page is for education and does not replace advice from your own veterinarian, who knows your dog. Increased thirst and urination alongside an anal mass warrants prompt veterinary attention.