Are There Signs That a Dog is Dying From Cancer?

Monica Tarantino, DVM
By Monica Tarantino, DVM. Reviewed by Katie Grzyb, DVM on Sep. 23, 2022
Are There Signs That a Dog is Dying From Cancer?

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

The American Veterinary Medical Association 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. The quality of life of the dog is the most important consideration.

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 you can work with your veterinarian to make the best decision 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 pet parents to know, as some forms of cancer have a good prognosis and respond to treatment, while others may not.

Some of the most common types of dog cancers include:

  1. Lymphoma: Cancer of the lymphatic system, including the lymph nodes. Some forms of this cancer respond well to chemotherapy that can put the cancer into remission for long periods of time. 

  2. Anal gland (sac) cancer: Cancer in the scent glands of the anus. This type of cancer tends to metastasize (spread) quickly to other organs in the body, although it can respond to chemotherapy.

  3. Bladder cancer: The most common type is transitional cell carcinoma, which develops in the walls of the bladder. Chemotherapy can be used to help treat this type of cancer, but unfortunately, it usually results in short survival times.

  4. Mammary gland (breast) cancer: This type of cancer develops in mammary gland tissue.  About half of canine breast tumors are malignant, half benign. A biopsy is necessary to determine malignancy. If caught early, the tissue can be removed. Your vet will start your dog on chemo, and lengthy survival times are possible.

  5. Hemangiosarcoma: This type of cancer is within blood vessels and is most commonly found in the spleen, liver, heart, or skin. Unfortunately, this is a fast-growing, quickly spreading cancer that responds poorly to chemotherapy. 

  6. Liver cancer: There are many types of cancer that can grow in or spread to the liver.  Some are aggressive, while others, such as hepatocellular carcinoma, are often localized and do not spread. Surgery to remove this type of tumor with or without chemotherapy can often allow for long survival times.

  7. Mast cell tumors: This type of cancer usually affects the skin. It can be benign and easily removed with surgery alone. Sometimes, however, the tumors spread to other organs.

  8. Soft tissue sarcoma: This type of cancer affects the connective tissue of the body—muscles, cartilage, and fat. If the cancer is diagnosed early and removed during surgery, dogs can live a long life. Sometimes surgery, including amputation, is needed to completely remove the cancer.

  9. Melanoma: This type of cancer is found in a dog’s skin or mouth. Skin melanoma can be treated with surgery, chemotherapy, and a melanoma vaccination. Oral melanoma tends to be locally invasive and often requires aggressive surgery for removal, followed by chemotherapy.

The Stages of Dog Cancer

Staging of cancer helps your veterinarian identify if the cancer has spread o 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 it is 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 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 solely in localized lymph nodes or has it spread to lymph nodes farther away? The farther 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 the 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 That Has 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. If you notice the following signs, you need to talk with your veterinarian about your dog’s quality of life and whether it’s time to put them down.

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

  1. Lymphoma: End-stage disease can cause dogs to act very 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).  

  2. 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. This type of cancer often spreads to the lungs, so your dog may be coughing or have trouble breathing. 

  3. Bladder cancer: Your 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. 

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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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. 

The Importance of Quality of Life

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

A good quality of life is unique to each dog and their lifestyle, so your veterinarian’s assessments, along with your own, are essential when discussing changes in behavior or medical health. 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 a veterinary oncologist, Dr. Alice Villalobos, and is a short test for owners to help determine if a pet has a good quality of life.

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

HHHHHMM includes:

  • 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. You can go over these criteria with your veterinarian to make an informed decision about what’s best for your pet.

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

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 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
  • 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 aggression

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

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 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.

Lap of Love’s calendar: Quality of Life Daily Assessment Calendar

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 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.

Featured Image:

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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