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Predicting Life Expectancy For Dogs With Cancer

Trying to predict the life expectancy for a dog with cancer is extremely difficult for vets, particularly considering that few pets with cancer will die naturally. When symptoms become severe many pet parents opt to euthanize their dog as a way to prevent suffering. Meaning that, for many dogs with cancer it is the pet owner that ultimately decides how long their dog lives following a cancer diagnosis.

With that in mind, if we look at an example of two dogs diagnosed with the same cancer. One dog may receive the very best treatment available for that particular cancer and go on to live a good quality of life for a year or more, whereas the other may belong to a family unable to pay for such treatment and may need to be euthanized soon after diagnosis.

It is also the case that some cancers are relatively easy to remove surgically if diagnosed early, whereas for other cancers surgery is not an option. For some chemotherapy may be effective, whereas other cancers may not respond to chemo at all.

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.

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:

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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