Mammary Tumors
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Article Written by Dr. Daniel A. Degner, Board-certified Veterinary Surgeon (DACVS)

Key Points

If a dog is spayed before the first heat cycle there is about a 0.5% chance that this pet will develop mammary cancer

The larger the breast tumor the greater the risk that it has spread to the lymph nodes, lungs, or other parts of the body

When a breast tumor has been found, there is a 50% chance that it is malignant and a 50% chance that it is benign

Of the malignant breast tumors, 50% have already spread at the time of diagnosis



  • Dogs have 5 mammary glands on each side (total of 10 breasts)
  • Cats have 4 mammary glands on each side (total of 8 breasts)
  • The lymph nodes in the groin and arm pits drain the mammary glands


Risk Factors for breast or mammary cancer in dogs

  • If a dog is spayed before the first heat cycle there is about a 0% chance that this pet will develop mammary cancer
  • The risk of developing mammary tumors increases with each successive heat that a dog
    • one heat cycle = 0.5%
    • two heat cycles = 8%
    • three heat cycles = 26%
  • Spaying a dog after 2 years of age will not decrease the risk for developing mammary cancer
  • The larger the breast tumor the greater the risk that it has spread to the lymph nodes, lungs, or other parts of the body
  • When a breast tumor has been found, there is a 50% chance that it is malignant and a 50% chance that it is benign
  • Of the malignant breast tumors found 50% have already spread at the time of diagnosis
  • If your pet has multiple mammary tumors, some may be malignant and some may be benign
  • Size matters:  if the tumor is less than 3 cm in size the recurrence rate is relatively low, versus greater than 3 cm has a fairly high recurrence rate
  • If the biopsy report indicates that the breast tumor has spread to the lymph nodes, lymphatic channels, or blood vessels the prognosis is poor
  • If the biopsy report indicates that the tumor is surrounded by cells called lymphocytes, a better prognosis is expected
  • If chest radiographs (x-rays) indicate that there is signs of metastasis (spread of cancer) to the lungs, long-term survival is not expected


Diagnostic tests prior to surgery

  • Compete blood cell count
  • Chemistry profile and urinalysis to evaluate function of the internal organs
  • Chest x-rays to rule out evidence of spread to the chest
  • Abdominal ultrasound
  • Fine needle biopsy of enlarge lymph nodes and mammary masses



  • If a single gland is affected, then only that gland is removed
  • If multiple glands on one side are affected, then the entire 5 glands on that side are removed
  • If multiple glands have tumors on both sides then both mammary chains are removed (all 10 glands are removed)
  • If the lymph nodes are within the resection zone, then they also are removed (and especially if they are enlarged)
  • If the groin region is difficult to suture closed, a flap of skin from the flank may be needed to reconstruct the area
  • The photo right shows a large mass (labeled M) in the mammary gland



  • If the tumor is malignant or shows evidence of invasion into the lymph system or blood vessels, chemotherapy likely will be recommended.
  • Tamoxifen usually does not have a good effect if the dogs has a malignant mammary tumor, as these usually have very low numbers of estrogen receptors. Side effects of this medication can include pyometra, vulvar enlargement, vulvar discharge, urinary tract infection, incontinence, low white blood count, death. Tamoxifen, in general, is not a good treatment for mammary tumors in dogs.


Mammary tumors in cats

  • Spaying female cats before the first heat has a significant sparing effect on the development of mammary cancer.
  • Mammary tumors in male cats
  • About 80 to 90% of the mammary tumors are highly malignant in female cats
  • Size matters:  tumors less than 2 cm in size have a better prognosis than tumors greater than 3 cm in size
  • Radical removal of both mammary chains should be performed if a large or multiple masses are present
  • If only a single pea sized mass is present, lumpectomy (or mammectomy) is acceptable instead of radical surgery
  • Chemotherapy should be considered to help control metastatic disease


Potential complications

  • Anesthetic death - rare
  • Infection - rare
  • Break-down of the incision, which may require resuturing of the wound or leaving it to heal on its own
  • Spread of cancer to other regions of the body (lymph nodes, lungs, bones)
  • Recurrence of cancer


  • Overley B, Shofer FS, Godschmidt MH, et al. Association between ovarihysterectomy and feline mammary carcinoma. J Vet Intern Med 19:560-563; 2005.
  • Skorupski KA, Overley B, Shofer FS, et al. Clinical characteristics of mammary carcinoma in male cats. J Vet Intern Med 19:52-55;2005.
  • Sorenmo KU, Shofer FS, Goldschmidt MH. Effect on spaying and timing of spaying on survival of dogs with mammary carcinoma. J Vet Intern Med 14:266-270; 2000.
  • Mauldin GN, Matus RE, Patnaik AK, et al. Efficacy and toxicity of doxorubicin and cyclophosphamide used in the treatment of selected malignant tumors in 23 cats. J Vet Intern Med 2:60-65; 1988.
  • Nieto A, Pena L, Perx-Alenxa MD et al. Immunohistologic detection of estrogen receptor alpha in canine mammary tumors clinical and pathologic associations and prognostic significance. Vet Pathol 37:239-247; 2000.
  • Poirier VJ, Hershey AE, Burgess KE, et al. Efficacy and toxicity of paclitaxel Taxol for the treatment of canine malignant tumors. J Vet Intern Med 18:219-222;2004.
  • Perez-Alenza MD, Tabanera E, Pena L. Inflamatory mamary carcinoma in dogs 33 cases. J Am Vet Med Assoc 219:1110-1114; 2001.
  • Saba CF, Rogers KS, Newman SJ, et al. Mammary gland tumors in male dogs. J Vet Intern Med 21:1056-1059; 2007.
  • Stratmann N, Failing K, Richeter A, et al. Mammary Tumor recurrence in bitches after regional mastectomy. Vet Surgery 37:82-86, 2008.
  • Simon D, Schoenrock D, Baumgaertner W, et al. Postoperative adjuvant treatment of invasive malignant mammmary gland tumors in dogs with doxorubicin and docetaxel. J Vet Intern Med 20:1184-1190; 2006.
  • Chang SC, Chang CC, Chang TJ, et al. Prognostic factors associated with survival two years after surgery in dogs with malignant mammary tumors 79 cases. J Am Vet Med Assoc 227:1625-1629;2005.
  • Perez Alenza D, Rutteman GR, Pena L, et al. Relationship betwen habitual diet and canine mammary tumors in a case-control study. J Vet Intern Med 12:132-139; 1998.
  • Novosad CA, Bergman PJ, O'brien MG, et al. Retrospective evaluation of adjunctive doxorubicin for teh treatment of feline mammary gland adenocarcinoma 67 cases. 42:110-120; 2006.

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

Board-certification by the American College of Veterinary Surgeons

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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