Anal Gland Cancer
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Article Written by Dr. Daniel A. Degner, Board-certified Veterinary Surgeon (DACVS)

Key Points

Anal sacs are glands that produce territorial marking secretions which are expelled in small quantities with each bowel movement

Anal sac adenocarcinomas can be identified via rectal palpation

The treatment of choice for anal sac adenocarcinoma is complete surgical excision

In general, dogs which have early, complete excision of the tumor are likely to have the best outcome



Anal sacs lie just inside the anus of most carnivorous species. They are paired structures (one sac on each side of the anus), which are lined by many glands. These glands produce secretions that are expelled in small quantities with each bowel movement as a form of territorial marking. In skunks the anal sacs are the scent glands which are released as a form of self-defense…we are all familiar with that smell.

Anal sac tumors arise from the glands of the anal sac, and may be benign (anal sac adenomas) or malignant (anal sac adenocarcinomas)—most anal sac tumors are of the malignant type. These anal sac adenocarcinomas make up approximately 2% of all skin tumors seen in dogs, and of these dogs, the majority are older females. There are no obvious breed predilections and this type of tumor occurs in both intact and neutered animals. Anal sac adenocarcinoma is very rare in cats, but has been reported.

The tumor itself is usually unilateral (affecting only one of the anal sacs), however bilateral tumors have been recognized, so both anal sacs should be carefully examined. The mass may be discrete or infiltrative, and can be very small (less than 1 cm in diameter) or quite large (up to 10 cm or more in diameter). It frequently produces a hormone which causes blood calcium levels to rise above normal levels. This is known as hypercalcemia of malignancy, and can cause problems with other organs such as the kidneys. In addition, anal sac adenocarcinomas have often metastasized (spread) by the time they are initially diagnosed. They may spread first to regional lymph nodes, such as the sublumbar lymph nodes, and later to the lumbar spine or more distant sites such as the liver, spleen, or lungs.


Clinical signs

Common clinical signs of affected animals include difficult or painful bowel movements, straining to have a bowel movement, ribbon-like stools, or swelling of the area around the anus. If hypercalcemia is present, other signs such as increased thirst, increased urination, decreased appetite, weight loss, vomiting, muscle weakness, and low heart rate may be noted. In the event that the tumor has spread to the sublumbar lymph nodes or lumbar spine, lower back pain or stilted gait may be present.



anal sac tumor fig 2, photo by Dan Degner, DVManal sac tumor fig 1, photo by Dan Degner, DVMAnal sac adenocarcinomas are usually identified during rectal palpation (Fig 1 and 2 show a large anal sac tumor), although these tumors are not always obvious when the anal sacs are palpated. During the rectal examination, it may also be possible to palpate enlarged sublumbar lymph nodes (possibly indicating metastasis).

If a tumor of the anal sac is palpated, complete blood count (CBC), serum chemistry profile, and urinalysis should be performed to identify possible hypercalcemia, evaluate systemic health, and help identify any other abnormalities. About 50% of these patients will have high blood calcium levels.

cytology of anal sac tumor, photo by Dan Degner, DVMIn addition, abdominal radiographs (X-rays) and abdominal ultrasound should be performed to evaluate internal organs and look for evidence of metastatic disease. Chest X-rays may also be needed to check the lungs for evidence of tumor spread.

Aspiration of some cells from the tumor or sublumbar lymph nodes may be performed so that they can be examined under the microscope; fig 3 shows malignant cells from the tumor. CT scans have also been used when further testing needs to be pursued.

The definitive diagnosis of anal sac adenocarcinoma, however, must be made by surgically removing the tumor or by taking a biopsy of the tumor and sending in a sample for analysis of the tissue by a pathologist using a microscope (called histopathology).


Treatment options

anal sac tumor after being removed, photo by Dan Degner, DVManal sac tumor being removed, photo by Dan Degner, DVMThe treatment of choice for anal sac adenocarcinoma is complete surgical excision (fig 4 shows the tumor being removed and fig 5 shows the tumor after it has been removed). If the sublumbar lymph nodes are enlarged, they should be removed as well because enlargement frequently indicates spread of the tumor to that site. If the lymph nodes are normal size on ultrasound imaging, they still should be removed as cancer cells are frequently found in these nodes. Hypercalcemia, if present, will usually resolve on its own within 24-48 hours of surgical excision of the tumor. In addition to surgery, chemotherapy is usually recommended to kill any remaining cancer cells. While the efficacy of chemotherapy has not yet been established, therapy with drugs such as a combination protocol of doxorubicin/cyclophosphamide may provide promising results for some patients. Another protocol involves the administration of actinomycin D or doxorubicin and 5-fluorouracil. We have seen many dogs go into remission for years following surgery and chemotherapy. Some of these cases also had spread to the sublumbar lymph nodes (which were also removed at the time of anal sac tumor excision)

Radiation therapy is another treatment option, which may be explored as adjuvant therapy. Cancer surgeons are seemingly going away from routine radiation of the anus, due to potential radiation-related side effects, but this treatment may be needed in some cases.


Potential complications

Even though rare, anesthetic death can occur. With the use of modern anesthetic protocols and extensive monitoring devices (blood pressure, EKG, pulse oxymetry, inspiratory and expiratory carbon dioxide levels, and respiration rate), the risk of problems with anesthesia is minimal.

Infection is also an unusual complication as strict sterile technique is used during the surgery and antibiotics are administered. A slight increase in the infection rate following anal sac carcinoma may be expected as this site is close to the anus (dirty).

Tumor-invaded lymph nodes are often closely associated with blood vessels, thus if sublumbar lymph nodes are removed there is a risk of bleeding during the procedure.

These lymph nodes are very close to nerves as well (especially those innervating the bladder), and removal may cause nerve damage leading to temporary or in some cases permanent post-operative urinary incontinence.

Fecal incontinence can follow surgery in a small percentage of animals.

Rectal prolapse can occur if the pet strains a lot and if the anal sphincter has poor function.

Anal stricture, an uncommon complication, will result difficulty passing stool.

Chronic fistula (a hole that develops between the rectum and skin around the anus) may develop if a portion of the rectum needs to be removed during the resective cancer surgery and the rectal incision fails to heal. This problem may require a temporary colostomy to divert feces from the area.


Postoperative evaluations

A biopsy of the tumor will be sent to a pathologist for analysis. This allows a definitive diagnosis to be made, based on the cell types present in the tumor.

At this time, other forms of treatment such as chemotherapy and/or radiation therapy may be recommended.

Even if surgery is the only treatment advised, periodic reevaluation is very important to help ensure that the anal sac adenocarcinoma has not recurred or spread to other areas of the body. The following may be recommended:

    Blood tests including calcium levels are often a good indicator of this, as levels will usually rise again if the tumor returns.

    Rectal examination

    Chest x-rays

    Abdominal ultrasound

The oncologist may also recommend ongoing low-dose chemotherapy, called metronomic therapy, to keep the cancer in check.



In general, dogs which have early, complete excision of the tumor are likely to have the best outcome. It is also important to note that many of these patients can be successfully managed, and continue to have a good quality of life for a number of years.

One report of five cases, in which only surgical excision of lymph node metastasis and the primary anal sac tumor resulted in a median survival time of 20.6 months. One dog had repeated removal of lymph nodes affected by metastasis and this dog survived 54 months.

Another series of 15 cases, the anal sac tumors were removed, however the metastatic lymph nodes were removed in only 4/7 cases. Radiation therapy was administered to the lymph nodes and mitoxantrone was administered (5 treatments). Median survival time was 31 months. Acute side effects of radiation were considered moderate to severe in 13/15 cases with signs of pain and perineal irritation being the most common. Four of 15 dogs had long-term straining during bowel movements due to radiation therapy.

In another study, which included 14 dogs with anal sac carcinoma, about 50% of these had metastasis to regional lymph nodes. In these cases, the anal sac tumor along with affected lymph nodes were removed and mephalan chemotherapy was administered. The median survival for dogs that had concurrent lymph node metastasis was 20 months and for the remaining dogs that had only the anal sac tumor (with no lymph node metastasis), the median survival time was 29.3 months.

The largest study, which included 113 dogs, showed that those treated with surgery and another treatment modality (radiation and/or chemotherapy) had a median survival time of 18.3 months versus 13.4 months with surgery alone. Dogs that had high level of calcium in the blood had a median survival time of 8.5 months versus dogs that had a normal blood calcium level had a median survival time of 19.5 months. Size also seems to matter: dogs with large tumors (>10 cm2) had shorter survival times.



  1. Hobson HP, et al. Surgery of metastatic anal sac adenocarcioma in five dogs. Vet Surgery 2006;35:267-270.
  2. Turek MM, et al. Postoperative radiotherapy and mitoxantrone or anal sac adenocarcinomas in the dog: 15 cases (1991-2001). Vet Comp Oncology 2003;1, 2:94-104.
  3. Anal sac tumours of the dog and their response to cytoreductive surgery and chemotherapy. Aust Vet J 2005 Jun;83(6):340-3.
  4. Williams LE, Gliatto JM, Dodge RK, et al. Carcinoma of the apocrine glands of the anal sac in dogs: 113 cases (1985-1995). J Am Vet Med Assoc 2003 15;223(6):825-31.

Frequently Asked Questions After Surgery

When should my dog have the first bowel movement after surgery?

  • Many dogs will not have a bowel movement for the first 4 to 5 days after surgery
  • Reasons that a dog will not have regular bowel movements after surgery include:
    • The dog has been fasted prior to surgery
    • Dogs do not eat well during the hospital stay
    • They frequently do not eat well when they go home
    • They are fed highly digestible food that produces little stool
    • Pain medication that contain narcotics (such as morphine, fentanyl patches, and tramadol) can be constipating
  • If a pet does not have a bowel movement on the 5th day of being home, a stool softener such as metamucil can be fed
    • Dose of metamucil is 1 tsp per 25 Kg mixed in with each meal (canned dog food); feed immediately after mixing, as the metamucil will gel the food and may make it less palatable

My pet had surgery and will not eat.  What can be done?

  • Dogs
    • Most pets will not eat their regular dog food after surgery, especially if it is kibble.
    • Offer a cooked diet having a 1:1 ratio of a protein source and carbohydrate source.  The protein source can be any meat (example: chicken breast, turkey breast, lean hamburger) that is low in fat and should be cooked (drain off all fat after the meat has been cooked).   The carbohydrate can be pasta, potato or white rice.
    • Try canned dog food; to enhance the flavor sprinkle a very small amount of garlic powder or chicken or beef broth (Chicken-in-a- MugTM or Beef-in-a-MugTM products)
    • Try Gerber strained meats for babies such as the chicken, beef, turkey, or veal
    • Try Hill's A/D diet available at most veterinary hospitals
    • Hand feeding: place a small amount of food in the mouth so that your dog gets the flavor
    • Warm the food slightly in a microwave, as the food will be more aromatic; stir the food before feeding and test the temperature on the bottom side of your wrist; it should only be luke warm.
    • Remember that most pets will not eat the first day or two after they get home from surgery
  • Cats
    • Offer smelly foods that contain fish such as tuna or smelly cat foods
    • Try Gerber strained meats for babies such as the chicken, beef, turkey or veal
    • Hand feeding:  with your finger place a small amount of food on the roof of your cat's mouth; use a syringe to get soft food into the mouth
    • Warm the food slightly in a microwave as the food will be more aromatic; remember to stir the food before feeding and test the temperature; it should be only luke-warm
    • Some cats will only eat dry food, try kibble if your cat normally has been fed that food
    • Petting and stroking your cat frequently will help to stimulate appetite
    • Remember that most pets will not eat the first day or two after they get home from surgery
    • Appetite stimulants such as cyproheptadine may be helpful
    • If your cat refuses to eat anything for 7 days a stomach tube or nasogastric tube should be placed to provide nutrition so that a serious liver problem (hepatic lipidosis) does not develop

My pet is vomiting.  What can be done?

  • The first thing for you to discern is whether your pet is vomiting or regurgitating.  Both will result in fluid or food being brought up.  Vomiting always will have heaving or retching of the abdomen prior to expulsion of the vomitus.  Regurgitation is not associated with heaving and the pet usually just opens the mouth and fluid or food will be expelled.  Usually the regurgited material will be clear or brown colored fluid. 
  • Next is to identify the cause of the vomiting or regurgitation.
  • Causes and treatment of vomiting after surgery
    • When some pets return home after a stay in the hospital they may drink excessive amounts of water at one time and then vomit; if this appears to be the case, the water should be limited to frequent smaller amounts.
    • Medications such as antibiotics, narcotics or nonsteroidal anti-inflammatory medication commonly cause vomiting after surgery.  In order to see which medication is causing the problem, the administration of each drug should be separated 2 hours apart.  Usually the pet will vomit or appear nauseated (drooling and sick look) within 1 hour of administration of the medication that they are sensitive to.  The antibiotic in some cases may be changed to a different one, or may be discontinued. 
    • Stomach upset from anesthesia is a potential cause of vomiting and will pass within a couple of days. 
    • An uncommon cause of vomiting after surgery is internal organ failure.  Blood testing will confirm this problem. For this reason vomiting should not be ignored if it persists for more than 24 hours.
    • If your pet had surgery of the bowels or stomach, vomiting is always a concern, as it may indicate that infection of the abdominal cavity, called peritonitis, is present.  Do not ignore this sign.
    • Symptomatic treatment of vomiting involves withholding food for 12 to 24 hours, then introducing small amounts of bland food such as rice and lean cooked hamburger, if your pet does not vomit after that then gradually wean him/her back onto the regular diet after 3 days.  In order to decrease the acidity of the stomach, Pepcid AC 0.5 mg/kg can be given by mouth twice daily for 5 days.  Metoclopramide and Cerenia are good anti-vomiting medications for dogs and cats.  You should always consult a veterinary healthcare professional before administering medication.
  • Causes and treatment of regurgitation after surgery
    • The most common cause of regurgitation is reflux of acid from the stomach into the esophagus while your pet is under anesthesia.  Acidic fluid from the stomach can cause a chemical burn of the esophagus and result in a bad case of heart burn, called esophagitis.  This results in poor motility of the esophagus, therefore water and food will accumulate in this structure.  In most cases, esphagitis is self-eliminating and will resolve within two or three days. 
    • If the esophagitis is severe the esophagus may develop one or more strictures.  A stricture is a narrowing or stenosis of the esophagus and does not allow passage of food down the esophagus, in regurgitation that lasts longer than one week.  This problem should be brought to the attention of your pet's doctor within the first two weeks so that it can be treated by ballooning the stricture (minimally invasive procedure, as it is done with the aide of an endoscope).  If an esophageal stricture is chronic surgery is needed.
    • Symptomatic treatment of regurgitation caused by esophagitis includes feeding bland food, and administering a coating agent (sucralfate) and an acid blocker (omeprazole or other).  Consult a veterinary health care professional if the regurgitation continues for more than a couple of days.

How do I know that my dog is in pain following surgery?

  • Signs of pain include
    • crying
    • biting if you get near the surgical site
    • grimacing (lips are pulled back and the the dog looks anxious)
    • tragic facial expression
    • panting
    • restlessness and unable to sleep; pacing
    • if abdominal surgery was done the pet will not lie down on the incision, or will continually sit up in spite of appearing very tired
    • the worst pain will be for the first 2 to 3 days after surgery

What can I do to control my dog's pain?

  • Narcotic medications that control pain: tramadol, butorphanol, Duragesic (fentanyl patch)
  • Anti-inflammatories used to control pain: Deramaxx, Rimadyl, Previcox, or Etogesic
  • If an orthopedic surgery has been done cold packing the surgical site may be helpful
    • A cold pack may be a pack of frozen peas, crushed ice in a Ziploc bag, or a cold gel pack; place a thin barrier between the skin and the cold pack.  An alternative to a cold pack is to freeze water in a styrofoam cup; after frozen cut the bottom of the styrofoam cup out. Cool the surgical site around the incision by rubbing the exposed ice directly on the skin in a circular pattern.  Cooling the surgical site helps to numb the area.

How do I know that my cat is in pain following surgery?

  • Pain is more difficult to assess in cats versus dogs, as signs can be more subtle and they usually do not vocalize when in pain
  • Signs of pain in a cat include the following:
    • biting if you get near the surgical site
    • growling or deep cry
    • not wanting to eat
    • hiding and not wanting to be near owner (remember that this could also be caused by the cat just being upset about leaving home and coming back)

What can be done for pain at home for my cat?

  • Pain medication such as buprenorphine or a Duragesic (fentanyl) patch
  • Tylenol will kill a cat as they lack abundant glutathione enzyme in the liver
  • Anti-inflammatories can be used, but the dose is much less than dogs

Is it okay for my pet to lick the incision?

  • If a dog licks the incision, the healing process may be delayed.
  • Licking can remove stitches and cause the incision to open
  • Licking can become a severe habit that is difficult to break
  • Licking can cause infection as the mouth has many bacteria
  • Dogs will frequently lick the incision when the owner is not watching such as at night time; if the skin looks red or excoriated the most common cause is from licking.
  • To stop your pet from licking the following can be tried:
    • Elizabethan collar can be placed on the neck; this will not help stop your pet from scratching at the region
    • Cervical collar (bite not collar) is a less awkward device and can be effective at stopping a pet from licking the surgical site
    • A tee shirt can be used to cover an incision on the chest or front part of the abdomen; gather the waist of the shirt up over the dog's back and wrap an elastic band around this part of the shirt.
    • A bandage or sock can be used to cover an incision on a limb; fasten the top of the sock to the dog's limb with tape.
    • Bitter apple can be applied around the incision; many dogs will continue to lick  after application of this topical
    • Bitter Apple and Liquid HeetTM (obtain this from a is used for sore muscles) mixed in a 2:1 ratio can be applied around the skin incision
    • Antipsychotic medication in some cases is needed

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What does it mean?

  • Four years of advanced training in surgery beyond the Doctor of Veterinary Medicine Degree

  • Experience in the development of new surgical treatments

  • Rigorous examination by the American College of Veterinary Surgeons to ensure competency in advanced surgical techniques

  • Assurance that a veterinarian is a surgical specialist

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