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15 Warning Signs of Cancer in Dogs



Cancer is increasingly common in pet animals, and as pets age, the likelihood of contracting some form of the disease increases substantially.  In fact, cancer accounts for almost half of the deaths of pets over 10 years of age. 

In breeds like the golden retriever it is estimated that between 60 and 80% will contract a form of cancer. But cancer is not restricted to geriatric canines, dogs as young as 4 years old may be diagnosed with it.

While dogs in general contract cancer at approximately the same rate as humans; cats tend to get fewer cancers, perhaps owing to their nine lives. Some cancers such as Hemangiosarcom and Oesteosarcoma have a higher rate of occurrence within certain breeds, suggesting a genetic component is probably at work.

If your dog’s breed has a propensity for developing a specific type of cancer, it is a good idea to familiarize yourself with the early warning symptoms of the onset of the disease.  Awareness of the signs of cancer in dogs combined with early detection and quick action can significantly improve the outcome for your pet.

sleeping senior dog
By Darnyi Zsóka via Wikimedia Commons

Common Warning Signs of Cancer in Dogs

If you suspect a combination of the following symptoms in your pet, consult your veterinarian promptly; when it comes to the health of your pet, it is always better to be safe now than sorry later.

  1. Foul Odors from the Mouth or Other Orifices: Foul Odors from the Mouth: If you detect offensive odors emanating from your dog’s mouth, and there has been no change in diet, you should have it checked out. Halitosis combined with excessive drooling, difficulty eating or swallowing can be a sign of oral cancer.   Bloody saliva indicates a prompt visit to the vet is in order. Bad odors from the ears, anal area or any other part of your pet’s body, should be checked out as well.  While food allergies, mites, impacted anal glands, infections from bites or scrapes or yeast infections can cause foul odors, it is best to seek veterinary advice to clear up any of these conditions and check for the underlying cause of the odor.
  2. Nasal discharge. This can be a sign of allergies, or especially if discolored or bloody, a symptom of cancer of the nasal and sinus cavities.
  3. Excessive Drooling and Difficulty Eating or Swallowing.  Excessive drooling, especially combined with a strong halitosis merits further investigation.  Anytime a dog has difficulty eating or swallowing you should consult a veterinarian immediately.  
  4. Difficulty Breathing and Coughing. Dogs having difficulty breathing  should be examined immediately.  For both humans and dogs, shortness of breath is a critical symptom.  Heart disease, lung cancer and hemangiosarcoma are potential underlying causes of breathing difficulties.  Early detection of any of these diseases can improve your dog’s prognosis.
  5. Excessive Panting.  It is normal for dogs to pant following exercise (for 20-30 minutes) or in extremely warm conditions.  Prolonged panting however may be a symptom of a severe injury or chronic illness such as heart failure, Cushing's syndrome, pneumonia or lung tumors.  
  6. Loss of Appetite. Dogs usually do not stop eating without a cause.  If your dog suddenly loses his appetite and there has been no change in diet, you should consider a trip to the vet, particularly if it is combined with some of the other symptoms on this list.  While this may not be a symptom of cancer, it could be a symptom of another serious issue where early intervention is beneficial.
  7. Lethargy. Lack of stamina or fatigue developing over a relatively short time frame can be symptoms of cancer.  Beyond normal aging, a dog that over a period of weeks or months that exhibits a noticeable decrease in activity levels should be seen by your veterinarian.  Other possible causes of lethargy and lack of appetite can include parasites such as tapeworms, roundworms, hookworms and whipworms, conditions that you will also want to address quickly.
  8. Depression.  You can’t put your finger on it, but Rover just doesn't seem to be himself.  Depressed dogs don’t seem to take pleasure in their usual activities; they tend to lie down away from the family activities exhibiting a decreased interest in their surroundings.  This can be a symptom of a change in the family dynamic or environment, but if there have been no changes to the family routine, depression combined with a several other symptoms on this list should be noted when discussing your dog’s health with your veterinarian.
  9. Changes in Bathroom Habits.  A dog that is normally well house trained begins soiling the house (and there have been no changes in the household dynamics to upset him) or the consistency of the bowel movement is unusual.  This symptom combined with depression were our first clues that something was wrong with our dog Kebe, prior to her being diagnosed with a branching cancerous tumor. Additionally, difficulty using the bathroom, frequent bathroom use or blood in urine or stool are all symptoms indicating a prompt visit to your vet is in order.
  10. Abdominal Distention. If your dog’s abdomen becomes bloated or distended it could be a sign of an accumulation of abnormal discharge within the body. Accumulation of fluids can be indicative of congestive heart failure and cardiac hemangiosarcoma.
  11. Lameness or Difficulty Walking.  Sudden onset of lameness or pain during exercise, when the dog has not engaged in any extreme physical activities can be indicative of arthritis or bone cancer (osteosarcoma).
  12. Weight Loss:  Just as in humans, cancer can cause its victims to lose weight dramatically.  If your pet has experienced weight loss, and you have not adjusted caloric intake or increased activity levels of your pet, then a trip to the vet is indicated.  If you notice sudden weight loss in your dog, along with other signs from this list (especially weight loss combined with decreased activity levels), be sure to mention it to your veterinarian.
  13. Vomiting or Diarrhea.  Vomiting and/or excessive diarrhea that continue for more than a day should be checked out by a vet.  At the very least, the dog may become dehydrated, a condition easily remedied by administration of fluids.  Prolonged vomiting or the inablility to hold down fluids and solids can indicate pancreatitis, kidney disease or digestive cancer.
  14. Lumps That are Unresolved or Growing. Not all lumps on or under your dog’s skin will be cancerous, but they are a cause for concern.  If the lump is growing rapidly, is ulcerated or bleeding, warm or painful to the touch you should consult your veterinarian. While it may just be a cyst, your vet can perform a needle biopsy and a veterinary pathologist can determine if the cells are cancerous or not.
  15. Sores That Don’t Heal. If your pet has wounds or sores that are not healing, it could be a sign of infection, skin disease, diabetes or cancer.
While many items on this list, when exhibited individually, are not cause for concern, an accumulation of 3 or more of these symptoms is reason to visit your veterinarian.

As your pet ages, it is a good idea to routinely examine him by stroking and petting his entire body. Tummy rubs and scratching around the ears and neck can aid in detecting any unusually bumps, and your dog will enjoy it too.  An annual physical examination along with annual laboratory analysis (for elderly pets) can be useful in early detection of a variety of disorders including those that affect the kidney, liver, heart or bowel.

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