Warning Signs of Cancer in Dogs

Veterinarian Examining Dog
Kerkez / Getty Images

A diagnosis of cancer in a beloved dog can be heartbreaking for any owner. This devastating disease is a leading cause of death in dogs, but if your vet can diagnose cancer early, your dog might have a better chance of survival with treatment. Learn the warning signs of cancer now so you will know what to do if your beloved canine companion becomes sick.

Many dogs with cancer will show no signs, at least initially. In other dogs, signs may be vague. Once a dog becomes sick enough, signs can be quite severe and seem to have a sudden onset. Routine wellness visits and health screening tests can help your vet detect illness early. This includes various common health issues ​and other more serious canine diseases, including cancer.

The following list is certainly not a complete list of cancer signs. In addition, these may be signs of other diseases. It's important not to ignore them. Contact your vet if you notice these or other signs of illness. Your vet will examine your dog and probably run tests to determine the problem. That being said, some signs of cancer in dogs may include the following.

  • 01 of 10

    Lethargy or Depression

    Sad dog
    Martin Rogers/Getty Images

    When dogs are lethargic, depressed or just "not right," it usually means something is wrong with their health. If it resolves on its own, then this is something to make a mental note of. However, if changes in activity level, mood and/or behavior persist for a few days or are combined with other symptoms, you should contact the vet.

  • 02 of 10

    Weight Loss

    Skinny dog in winter

    Ivan Bandura/Flickr CC 2.0 

    There are a variety of health problems that can cause a dog to lose weight. Sometimes dogs with normal appetites even lose weight. Talk to your vet if your dog seems to be losing weight (without trying). It might be cancer or another disease.

  • 03 of 10

    Appetite Changes

    Dog sitting in front of food bowls

    Les Chatfield/Flickr CC 2.0 

    A decrease in appetite often goes along with weight loss. However, some dogs might still eat fairly well and maintain weight but seem less enthusiastic about food or simply picky. Trouble eating or swallowing is also something to act upon. Contact your vet if your dog's eating habits change, especially if it occurs in conjunction with other signs.

  • 04 of 10

    Vomiting or Diarrhea

    Dog squatting to poop, man watching

    Ann Cutting/Getty Images

    Vomiting and diarrhea may occur for a number of reasons. While not always associated with cancer, they are things to address regardless of cause. If vomiting or diarrhea persist and treatments for common causes don't work, your vet may recommend additional diagnostic tests to look for cancer.

    Similarly, difficulty urinating and/or constipation should be noted and reported to the vet.

    Continue to 5 of 10 below.
  • 05 of 10

    Lumps and Bumps

    Skin growth on dog's side

    bobby_j_99/Flickr CC 2.0 

    Lumps, bumps, growths, masses, or tumors can appear just about anywhere on or in the body. Many lumps and bumps are benign growths. Some may come with age or genetics. Your vet should be the one to decide which growths are concerning.

    See your vet if your dog develops new lumps/bumps. In addition, visit the vet if existing lumps/bumps change in shape or size, rupture, develop a discharge or if they begin bothering your dog. Your vet will run tests to pinpoint the type of lump and determine if treatment is necessary.

  • 06 of 10

    Persistent Lameness or Pain

    Limping dog

    Fred Rockwood/Flickr CC 2.0 

    A mild limp can be related to an injury, but, if rest and medications do not make the problem go away, be sure to let your vet perform X-rays and other tests as indicated. Sudden, severe pain accompanied by a limp is always a cause for concern. Bone cancer, can cause either persistent or acute lameness, but diagnostic testing is needed to differentiate it from other chronic conditions, like arthritis.

    Pain in the abdomen and other areas of the body can also be caused by a number of things, and cancer is one of them.

  • 07 of 10

    Distended Abdomen

    Relaxed Dachshund All Stretched out for a Belly Rub

    Leslie/Flickr CC 2.0 

    If your dog's abdomen looks enlarged or bloated, you should go to the vet as soon as possible. There are a few conditions that can cause the abdomen to become distended. A tumor in the abdomen may lead to fluid buildup, enlarging the abdomen even if the tumor itself is still relatively small. Anther potential cause is a deadly condition called GDV or "bloat."

  • 08 of 10

    Abnormal Discharge or Bleeding

    Closeup of a Dog's Eyes

    Cogdogblog/Flickr CC 2.0 

    Blood or drainage from the skin, nose, mouth, eyes, ears, anus, or genitals are all reasons to see the vet right away. Potential causes of this can range from minor infection to major illness. Even if the reason is not cancer, it's an issue that needs attention.

    Continue to 9 of 10 below.
  • 09 of 10

    Strong Odor From Mouth

    Gingival Growth

    Life Lenses Photography/Flickr CC 2.0 

    Your dog's breath might be bad due to dental disease, and this alone is reason enough to see the vet. However, strong odors, especially when they come on suddenly and/or no dental disease is present, can also be seen with tumors within the mouth. Additional signs to look for include swelling in the face and apparent shifting of the teeth.

  • 10 of 10

    Abnormal Gum Color

    Lab with normal pink gums and tongue

    Steven Jackson/Flickr CC 2.0 

    A healthy dog's mucous membranes (gums, cheeks, insides of eyelids) and tongue should be nice and pink (black color from pigment is also normal). Pale, white, gray, or blue mucous membranes indicate a big problem.

    Additionally, a yellow tinge to the mucous membranes, whites of the eyes, and or skin is indicative of jaundice that is typically seen with liver disease or disorders affecting red blood cells.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.
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  1. Dog Cancer - Symptoms, Diagnosis & TreatmentThe Drake Center For Veterinary Care, 2020

  2. Cancer In PetsAmerican Veterinary Medical Association, 2020

  3. Stomach Cancer In Dogs | Bluepearl Pet HospitalBluepearl, 2020

  4. 10 Warning Signs Of CancerAnimal Cancer Foundation, 2020

  5. Normal Vital SignsNorth Mankato Animal Hospital