Symptoms Of Cancer in Dogs

When we discuss symptoms of illness in dogs, we use the term signs, which is more accurate. Many of the signs of cancer in dogs are shared with other illnesses. Seeking care promptly is key.

Key Takeaways

  • Cancer can develop anywhere in your dog’s body.
  • Cancer can develop in dogs of all ages. It is more common in older dogs.
  • With appropriate testing performed it is very uncommon to mistake other illnesses for cancer.
  • Physical examination and annual wellness screening are the initial ways that vets monitor for cancer. Additionally, x-rays, biopsy and other testing may be necessary.
  • There is no one breed of dog that is most prone to cancer.
  • Sometimes blood tests can identify certain cancers. However, there is no blood test that can be performed to screen for all cancer types.

Symptoms of Cancer in Dogs

When we veterinarians talk about symptoms of cancer in dogs, we often call them signs of cancer, instead. That’s because symptoms are medical issues that are experienced by a person.1

  • A symptom is a manifestation of disease apparent to the patient himself. But dogs can’t report their own symptoms to us, so in veterinary medicine we don’t use the word symptoms.
  • A sign is a manifestation of a disease that the veterinarian perceives, so your veterinarian may discuss the “signs” your dog displays.

Understanding why your veterinarian discusses signs, not symptoms, is helpful and a reminder of how challenging the assessment of dogs with cancer can be in comparison to people. Our patients do not speak. They cannot offer their assessment of what is wrong, such as being able to say, “it hurts here.”

That’s why we veterinarians have to rely on other methods of diagnosis. We rely on our examination, clinical observations, and collecting a detailed history of your dog from you.

Nonspecific Signs of Cancer in Dogs

Nonspecific signs of cancer are signs that we might see with other illnesses, as well.

Examples of nonspecific signs that could occur in cancer, but also in many other diseases, are:

  • Weight loss
  • Lethargy
  • Vomiting/diarrhea
  • Lameness
  • Abnormal discharge from the nose, mouth, rectum or vulva
  • Halitosis (foul odor from the mouth)
  • Changes in behavior

This is only a partial list of the nonspecific signs of cancer in dogs.

Early Signs That May Indicate Cancer in Dogs

Many of the nonspecific signs listed above can also be considered early signs of cancer in your dog.

Additionally, masses, swellings or bumps that develop quickly or change in appearance and wounds that will not heal could be more specific indicators of cancer.

Recognizing an Emergency

Seek emergency care whenever there is an abrupt change in your dog’s condition.

Rapid onset weakness, difficulty breathing, disorientation, seizure, pallor (light colored gums), severe vomiting or diarrhea, inability to urinate, bleeding, and acute pain are all signs that your dog may be having a life-threatening emergency.

When to Seek Veterinary Care

Signs are much harder to recognize in dogs than symptoms are in humans. For example, it might take a long time for you to notice your dog’s weight loss because you see your dog each day and changes over time can be difficult to see.

Once you recognize signs of possible illness pursue your concerns. Whenever you notice that there has been a change in your dog’s condition you should schedule a visit with your vet.

Remember, nonspecific signs can be signs of a variety of other illnesses that can be very serious. It is much better to have your dog evaluated promptly if you have concerns.

Trust Your Gut

You are the most astute and valuable observer of your dog. If your dog’s normal behavior, appetite, or energy level change, or masses develop, seek veterinary care. If your dog’s condition abruptly changes, they become weak, unresponsive, have seizures, collapse or develop other rapid and dramatic signs, seek emergency veterinary care.

  1. NCI Dictionary of Cancer terms: Symptoms. National Cancer Institute. Accessed April 28, 2023.
  2. King L. Signs and Symptoms. (1968) JAMA.206(5):1063–1065. doi:10.1001/jama.1968.03150050051011.


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