Cancer In Pets Outlined - CanadaVet

"I'm sorry, it's cancer."

Those four little words are among the most devastating a pet owner can ever hear. Many of us love our pets like children, and we don't want to see them suffer or live in pain. Unfortunately, the rates of cancer in dogs are similar to those in humans, and it has been estimated that between 800-900 out of every 100,000 dogs will develop cancer in their lifetime. The rate of cancer in cats is slightly less than this, but cancer is still responsible for 32% of all causes of death in cats.


This article aims to outline the most common types of cancer in dogs and cats, some of the symptoms of each and, others to be on the lookout for. It also explores treatment options, causes of cancer in pets, and things that you, as a pet owner, can do to reduce your pet's risk of developing cancer.



Common Types of Cancer in Dogs & their Symptoms

There are over 100 types of cancer in dogs, and it can affect every and any organ in their body. Some of the most common types of cancer in dogs include:


Mast Cell Tumours

Mast Cell Tumours are a form of skin cancer that often appears as a lump but can also affect the internal organs. Although it doesn't usually cause death; it is more likely to develop in certain breeds such as golden retrievers, Labrador retrievers, Boston terriers, boxers, and pitbulls, which typically affect middle-aged and older dogs.


Just like humans, dogs can get melanoma as well. It typically presents as a brown or dark spot in or around a dog's mouth but can also be pink or multi-colored. It is most commonly seen in dogs over ten years of age, and miniature poodles, cocker spaniels, chows, and golden retrievers are the most likely breeds affected by melanoma.


Lymphoma is white blood cell cancer commonly found in lymph nodes and other organs containing lymph tissue, such as the spleen, liver, gastrointestinal tract, and bone marrow. Over 30 types of lymphoma can be found in dogs, all with different symptoms depending on the location of cancer; some will cause the lymph nodes to become swollen, and others will cause vomiting and diarrhea.

Osteosarcoma (bone cancer)

Osteosarcoma is the most common type of bone tumor found in dogs and primarily affects the limbs but can also develop in the skull, spine, and ribs. Giant breeds of dogs such as Greyhounds, Great Dane, Mastiffs, Irish Wolfhounds, Dobermanns, and Rottweilers are particularly prone to developing osteosarcoma. As a result, they may develop tumors younger than other breeds. Swelling, lameness, a loss of appetite, and reduced levels of activity are all symptoms that a dog may exhibit if they have osteosarcoma. In addition, osteosarcomas can be very painful, so watch for signs your dog may be in pain, such as restlessness and other behavioral changes.


Hemangiosarcoma develops from the cells that create blood vessels and can affect the spleen, liver, heart, and skin. Sunlight can cause hemangiosarcoma on the belly skin, the inner thighs, and the eyelids of dogs with pale or pink skin and thin fur. Hemangiosarcoma typically affects middle-aged to older dogs, and German Shepherds, Golden Retrievers, and Labrador Retrievers are more susceptible than other breeds. Symptoms vary according to the location of the hemangiosarcoma. They can include the formation of a bump or swelling under the skin, unexplained weight loss, decreased appetite, belly swelling, lethargy, a cough, and pale gums.



Common Types of Cancer in Cats & their Symptoms

Cats are also susceptible to various cancers, and while cats continue to live longer and longer lives, cancer rates in cats will continue to climb. Some of the most common types of cancer in cats include:



Lymphoma is white blood cell cancer commonly found in lymph nodes and other organs containing lymph tissue, such as the spleen, liver, gastrointestinal tract, and kidneys. Cats between the ages of 2 and 6 are commonly affected by lymphoma, but it can affect cats of any age. Before the Feline Leukemia Virus (FeLV) vaccine was developed, FeLV was the leading cause of lymphoma in cats. Again, the symptoms of lymphoma can be varied but often include abnormal swelling, weight loss, and difficulty eating or swallowing.

Squamous Cell Carcinoma (skin cancer)

Squamous cell carcinoma often appears on a cat's nose, the tips of its ears, and the lids. It is commonly caused by excessive sun exposure, and cats with white fur or very light skin are at a greater risk of developing squamous cell carcinoma. SCCs can be painful and often appear as a raised, reddened area or look like a cauliflower-like growth or deep sore.


Fibrosarcoma is a cancer of the soft, fibrous, and connective tissues. It can occur anywhere on a cat but commonly affects the skin and presents as skin mass with no signs of pain or discomfort.

Mammary (breast) cancer

Mammary cancer is the third most common type of feline cancer, which affects the mammary glands and is most commonly found in cats over ten years of age. A small lump just beneath or next to a nipple is often the first sign of mammary cancer which can spread to other areas of the body such as the lymph nodes, liver, or kidneys. Siamese cats have twice the risk of mammary cancer than other cat breeds.

Other symptoms, such as pain, fever, anemia, drinking too much water, producing excessive urine, and ravenous appetite, may also be cancer in cats, depending on the tumor type and its effects on the body.



Causes of Cancer in Pets

Several known carcinogens may contribute to the development of cancer in pets, including ultraviolet radiation from excessive exposure to the sun; second-hand cigarette smoke; a variety of herbicides, insecticides, and pesticides used in agriculture; and air pollution and smog in urban areas. Other common substances identified as carcinogens include nickel, uranium, benzidine, benzene, radon, vinyl chloride, cadmium, and asbestos.

The female reproductive hormones estrogen and progesterone found in unspayed cats also triples a cat's risk of developing cancer (particularly mammary cancer).



Just as in humans, the type of cancer, the location and staging of the tumor, and your pet's prognosis all play a role in determining the kind of treatment your pet will receive.

Surgery remains one of the most common treatments to remove a lump or limb to prevent the spread of cancer cells to other parts of the body. Surgery is often combined with radiation therapy or chemotherapy to kill any remaining cells after removing the tumor. Dogs tolerate chemotherapy exceptionally well and don't lose their fur.

Other cancer treatments include immunotherapy, injecting your pet with an anti-cancer vaccine to strengthen their immune system, and stem cell transplants, common in pets with blood cancers (leukemia). Your vet may also suggest that your pet might be suitable to partake in a clinical trial of a new medication shown in earlier studies to help treat the type of cancer your pet has.


How Can I Reduce My Pets Chance of Developing Cancer?

While some risk factors, such as breed type and genetics, are unavoidable, there are several things you, as a pet owner, can do to reduce your pet's risk of developing cancer.

Female dogs and cats that have not been spayed before they first come on heat can be up to 200 times more likely to develop mammary cancer than those who are not spayed until they are 12 months or older. And neutering your male cat or dog eliminates their risk of developing testicular cancer.

Feeding your pet quality and nutritionally appropriate diet gives your pet's body the best chance at fighting off both cancer and other diseases.

Limiting the amount of time your dog spends in direct sunlight will also reduce its risk of developing skin cancers such as squamous cell carcinoma, and you should never smoke around your pets.

Regular vet visits that include a thorough physical examination are essential, especially for older dogs. The earlier a cancer is detected, the better the chance is that treatment will be able to eliminate the tumor successfully.


Final Tips

A cancer diagnosis isn't necessarily a death sentence anymore. Dogs share over 80% of their genome with humans meaning that human treatments for cancer are often successful for dogs. In addition, scientific advancements mean that more and more treatments successfully eliminate cancer. However, treatment for pets with a limited life expectancy may extend their life for several years and should be considered against your pet's quality of life. Your pet's veterinarian is the best person to discuss treatment options with. There are even specialist veterinary oncologists who exclusively treat pets with cancer that you may wish to seek to provide specialized care for your pet.