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With pets living longer than ever, cancer has become a diagnosis that we see more commonly in older dogs.

The American Veterinary Medical Association (AVMA) reports that one in four dogs will develop cancer at some time in their life and that 50% of pets over the age of 10 will develop cancer.

While there are treatments and methods for achieving remission or even curing cancer in dogs, each case is different, and the quality of life of the dog needs to be paramount.

However, once treatment is no longer an option, it is time to start discussing end-of-life care with your veterinarian. But how do you know when it’s time?

Here’s an explanation of the stages of cancer and how to evaluate your dog’s quality of life so that you can work with your veterinarian to make the best decisions for your dog.

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

If your veterinarian has diagnosed your dog with cancer, they will likely try to determine both the type of cancer and the stage.

These are important for veterinarians to know, as some forms of cancer will have a good prognosis and respond to treatment while others may not.

The Stages of Dog Cancer

Staging of cancer helps your veterinarian identify if the cancer has spread to other locations in the body, which can change both the prognosis and appropriate treatment plan.

A variety of staging systems exist depending on the type of cancer, so you can’t really define each stage in general. However, many cancers are staged using the TNM system.

The TNM system was adapted for dogs from the World Health Organization (WHO) cancer-staging system used for people. 

Each subcategory of the TNM system helps identify the aggressiveness of the cancer:

  • T: Tumor size. How big is the tumor, and is it invading other vital structures in the immediate vicinity of the tumor?

  • N: Lymph Nodes. Identifies whether the cancer is also in the body’s lymphatic system. Is it in just the local lymph nodes or has it spread to lymph nodes further away? The further the spread, the worse the prognosis.

  • M: Metastasis. Identifies if the cancer has spread to other organs in the body. Any spread to new organs worsens the prognosis.

In general, once cancer has spread to other parts of the body, it can be more difficult to treat effectively with chemotherapy or radiation therapy. Therefore, cancers that have spread from the original tumor to lymph nodes or other parts of the body are ranked higher in staging system, which means a worse prognosis.

End stages or final stages of cancer in dogs occur once the cancer has infiltrated organs to the point that they are unable to maintain normal body functions or reasonable quality of life.

How Do I Know When to Euthanize a Dog With Cancer?


Both early- and late-stage cancers require diligent monitoring. Pay close attention to changes in your dog’s behavior and routine.

Dogs can’t tell us how they are feeling, so these sometimes subtle changes can help you evaluate your pet’s pain and overall well-being.

The Importance of Quality of Life

The most important factor in deciding when to euthanize a dog with cancer will be deciding if your dog has a good quality of life.

A good quality of life will be unique to each dog and their lifestyle, so your and your veterinarian’s assessments on changes in behavior or medical health are essential.

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

How to Evaluate Quality of Life in a Dog With Cancer

To help determine if it is time to euthanize a dog with cancer, you can take the following steps to evaluate and discuss their quality of life with your veterinarian  

Take an at-home quality of life test.

The Quality of Life Scale (Also known as the HHHHHMM scale) was created by Dr. Alice Villalobos and is a short test for owners to take to help determine if a pet has a good quality of life. 

This test can be taken as often as you suspect it is necessary throughout your pet’s life. But you need your veterinarian’s input after you’ve made your own assessment.

Make an appointment with your veterinarian to discuss your pet’s quality of life.

Your veterinarian is a critical part of your pet’s care and can help provide information and insight into your pet’s condition and quality of life in ways that you may not have noticed or realized.

They cannot make the decision of euthanasia for you, but they can be an instrumental resource in your pet’s specific health care plan.

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

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

  • Labored breathing: Difficulty catching their breath; short, shallow breaths; or wide and deep breaths that appear to be labored

  • Inappetence and lethargy

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

  • Restlessness, inability to sleep

  • Unusual or unexplained vocalization or moaning

  • Antisocial behavior, like hiding or unexplained aggression

Use a calendar to mark each good day and bad day.

Often pets will 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 an overall bad day.

Once the number of bad days outweighs the good days in a week, it’s time to discuss humane euthanasia with your veterinarian.

Discuss with family and friends who know both you and your pet.

Sometimes having a second opinion about your dog and their quality of life from someone who knows them can give perspective on your pet’s condition and help in the decision-making process.

Allowing family and friends to know you are facing this dilemma can allow them to be a support system for you and help keep the focus on making the right decision for your beloved pet.

Your Veterinarian Is There to Help

If you have done the above steps and are still unsure if you should euthanize, understand that this is normal.

Make an appointment with your veterinarian to discuss your concerns and thoughts with them. They can help support you during this difficult decision.

One of the nicest things we can do for our beloved companions is to allow them to pass in peace and with dignity by limiting the suffering they might experience in their final moments or days.

It is never an easy decision, but ultimately it is a humane one.

By: Dr. Monica Tarantino, DVM

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