Signs a Dog Is Dying of Cancer

Monica Tarantino, DVM
By Monica Tarantino, DVM. Reviewed by Sandra C. Mitchell, DVM, DABVP on Jan. 30, 2024
A dog sleeps on the floor.

In This Article

Dog Cancer Stages

Cancer has become a common diagnosis in older dogs. There are various treatments and methods for achieving remission or even curing cancer in dogs.

However, each case is different, and your pup’s quality of life is the most important consideration to make as a pet parent. By looking at the world through the eyes of your pet, you will likely be able to decide if they have a good quality of life.

For example—does your dog still like to do all their favorite things, such as go for a walk, snuggle, enjoy treats, or sit in the sun? If so, their quality of life is good.

If treatment is no longer an option or quality of life can’t be obtained, it’s time to start discussing end-of-life care with your veterinarian. But how do you know when it’s time?

Let’s look at the stages of cancer in dogs, common signs of advanced cancer, and how to make the best decision for your pup.

Dog Cancer Stages

Staging of cancer helps your vet to understand if the cancer has spread to other locations in your dog’s body, which can change both the prognosis and appropriate treatment plan.

A variety of staging systems exist depending on the type of cancer, so it’s difficult to define each stage in general terms. However, many cancers are staged using the TNM system, which was adapted for dogs from the World Health Organization (WHO) cancer-staging system used for humans.

Each subcategory of the TNM system helps identify the aggressiveness of the cancer. They include:

  • T: Tumor size—How big is the tumor, and is it invading other vital structures in the immediate area around the tumor?

  • N: Lymph nodes—Identifies whether the cancer is also in the body’s lymphatic system. Is it solely in localized lymph nodes or has it spread to lymph nodes farther away? The greater the spread, the worse the prognosis.

  • M: Metastasis—The cancer has spread to other organs in the body. Any spread to new organs worsens a dog’s prognosis.

Once cancer has spread to other parts of a dog’s body, it can be more difficult to treat effectively with chemotherapy or radiation therapy. Because of this, cancers that have spread from the original tumor to lymph nodes or other parts of the body are ranked higher in the staging system.

End stages of cancer in dogs occur once the cancer has affected their organs and they are unable to maintain normal body functions or good quality of life.

Does a Certain Stage of Cancer Mean That a Dog Is Dying?

Knowing what stage your dog’s cancer is doesn’t necessarily tell you that your dog is dying. 

Never decide based on what disease your dog has “on paper” or just looking at the staging. Make your decisions based on how your pet is feeling, how well they tolerate treatment, what the potential outcomes are likely to be, and your vet’s advice.

Late-Stage Cancer Symptoms in Dogs

Both early- and late-stage cancers require near-constant monitoring.

Pay close attention to changes in your dog’s behavior and routine. Dogs can’t tell us how they are feeling, so these changes can help you evaluate your pet’s pain and overall well-being.

Here are some symptoms that you may see in the late stages of different types of cancers:

  • Lymphoma—End-stage disease can cause dogs to act lethargic, vomit, have diarrhea, eat less, or have no appetite, and lose weight.

    • If the lymph nodes are very large, they can affect breathing because they are blocking the throat. You may notice that your dog has trouble breathing or noisy inhalation (stertor).  

  • Anal gland (sac) cancer—You may notice wounds or large, invasive growths around the anus, and you may also see bleeding, infection, pain, and/or difficulty defecating and/or moving around.

  • Bladder cancerYour pet could have trouble urinating, with signs that include straining, frequent small puddles, blood in the urine, difficulty walking, back pain, and/or complete blockage if the tumor grows large enough to obstruct the flow of urine. 

  • Mammary gland (breast) cancer—Large, lump-like tumors that outgrow their blood supply can lead to bleeding, dying tissue, severe infection, and pain.

  • Hemangiosarcoma—Often, this cancer is not diagnosed until it has progressed. Rupture of tumors growing in the spleen, liver, or heart lead to bleeding and eventually death due to severe blood loss.

    • This type of cancer also spreads to the lungs, causing coughing and trouble breathing.

  • Liver cancer—End stages of certain liver cancers have signs such as vomiting, diarrhea, decreased/absent appetite, weight loss, bleeding into the abdomen, and/or liver failure.

  • Mast cell tumors—End stages of aggressive forms of mast cell tumors often affect body organs such as the liver and spleen, leading to lethargy, vomiting, diarrhea, weight loss, no appetite, and sometimes, anaphylactic reactions.

  • Soft tissue sarcoma—Left untreated, these masses can cause large, hard masses that cause pain, make it hard for your dog to get around, lead to wounds, and cause a general unwell feeling as well as weight loss.

  • Melanoma—The oral version of this type of cancer can lead to difficulty eating, chewing, or swallowing, leading to weight loss, pain, infection, and even trouble breathing if the growths are enlarged. 

If you notice any of these signs, speak with your vet about your dog’s quality of life and whether humane euthanasia is a good option for your pup.

Signs a Dog Is Dying of Cancer

If your dog is exhibiting any signs that are decreasing their quality of life and are not able to be soothed with medication, it’s a sign that cancer is winning the battle.

When to Humanely Euthanize a Dog With Cancer

Be aware of signs of pain, discomfort, and distress in your dog.

These signs are often dramatic and can be a clear indicator that humane euthanasia should be considered:

  • Labored breathing or difficulty catching their breath

  • Lack of appetite

  • Lethargy

  • Losing the ability to defecate or urinate, or urinating and defecating but not being strong enough to move away from it

  • Restlessness, inability to sleep

  • Unusual or unexplained vocalization or moaning

  • Antisocial behavior, such as hiding or unexplained reactivity

Pets will often have ups and downs during their final months. At the end of every day, make a mark on a calendar to note if you believe your pet had an overall good day or a bad day.

What Is the Quality-of-Life Scale for Dogs?

A good quality of life is unique to each dog and their lifestyle. Your veterinarian’s assessments, along with your own, are essential when discussing changes in your pup’s behavior and health.

When your dog no longer has a good quality of life, then it’s time to discuss humane euthanasia with your vet.

But how can you tell?

You can take an at-home test. The Quality-of-Life Scale (HHHHHMM scale) is a short test for pet parents to help determine if their dog has a good quality of life.

HHHHHMM means:

  • Hurt

  • Hunger

  • Hydration

  • Hygiene

  • Happiness

  • Mobility

  • More good days than bad

Each factor is scored from 1 to 10 to help you evaluate your pet’s quality of life.

Lap of Love, a nationwide network of veterinarians dedicated to end-of-life care, also has several resources that can help you determine your pet’s quality of life:

After taking an assessment at home, go over the results with your vet. They will help you to make an informed decision about what’s best for your dog.

If you are still unsure if humane euthanasia is the right decision, understand that this is normal. Speak with your vet to discuss your concerns and thoughts with them—they can help support you during this difficult decision.

Remember, one of the kindest things you can do for your beloved dog is to allow them to pass in peace and with dignity.

Featured Image: Chalabala/iStock / Getty Images Plus via Getty Images

Monica Tarantino, DVM


Monica Tarantino, DVM


Dr. Monica Tarantino is a small animal veterinarian and pet parent educator. She's on a mission to help senior cats and dogs around the...

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