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As a pet parent, one of the most devastating things you’ll hear from your veterinarian is when your beloved dog or cat is diagnosed with cancer. Even though it’s one of the most common diseases for pets over the age of 10, it’s not something pet parents really prepare for or even expect in their pets’ lifetime. We ask ourselves, “Why did this happen? Is there something I could have done to prevent it?”

How do pets get cancer? Statistics show that one in four dogs and one in six cats will develop cancer during their lifetime. Unfortunately, the direct cause for the most common cancer in pets is still unknown. This is because in nearly all cases, cancer is typically caused by long-term accumulation and combination of genetic and environmental factors.


Here are 5 of the most common factors that have a strong link between cancer and pets:


  1. Genetics play a role in cancer development, particularly in dogs.

Cancer can affect all pets, however, some dog breeds are more prone to developing cancer than others just because of their genetic makeup.

According to the Morris Animal Foundation, the dog breeds that are at high risk of cancer are:

  • Bernese mountain dog
  • Boxer
  • Chow Chow
  • Cocker spaniel
  • Collie
  • Golden retriever
  • Labrador retriever
  • Pug
  • Rottweiler
  • Scottish terrier
  • Shar-Pei


  1. Environmental pollutants and harmful chemicals have been linked to cancer in both dogs and cats.


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Many studies have shown an increase in the accumulation of known carcinogens from second-hand cigarette smoke in our pets’ bodily tissues. In dogs, second-hand smoke has been linked to tumor formation in the lungs and an increase in nasal adenocarcinoma, particularly in long-nosed breeds.

The carcinogens present in cigarette smoke may be passively deposited on the fur of the cats, and when cats groom themselves, they inadvertently ingest these chemicals, which can initiate an inflammatory response that can predispose cancer.

Second-hand smoke is not the only environmental toxin with the potential to cause pet cancer. A recent study found a strong link between exposure to harmful chemical herbicides and insecticides and the development of cancer in dogs.

Pet parents should strive to minimize their pets’ exposure to these harmful chemicals and discuss any concerns they may have with their veterinarian.


  1. Viruses can induce tumorigenesis, or the creation of cancer.

There is a link between Feline leukemia virus (FeLV) and Feline immunodeficiency virus (FIV) and development of lymphoma in cats.


According to PetMd: FeLV and FIV are retroviruses that affect cats and can cause a variety of clinical signs in infected animals. Many cats that test positive for either virus as kittens may not show any clinical signs for several years. Cats that test positive for FeLV are 60 times more likely to develop lymphoma than cats that test negative for this virus, and cats that are FIV positive are five times more likely to develop lymphoma. Cats that test positive for both viruses concurrently are 80 times more likely to develop lymphoma.


Dogs can develop papillomas or oral skin tumors, after being infected with a papilloma virus, which is contagious from other dogs. Fortunately, this occurs mainly in young dogs and frequently resolves without treatment.


  1. Sex hormones also play a role in the development of pet cancer.

Studies show that there is an increased risk of mammary cancer in un-spayed female dogs and cats. Hormones that are released during heat cycles cause mutations within the mammary tissue, leading to the development of tumors.


According to PetMD: Dogs spayed before their first heat cycle have a 0.5% chance of developing mammary cancer during their lifetime. This increases to 8% if they are spayed after they have experienced one heat cycle, and 26% if spayed after they have experienced two heat cycles.


Cats spayed before six months of age are seven times less likely to develop mammary tumors than cats spayed after six months of age.


  1. Solar radiation (i.e. sun bathing) increases the risk of skin cancer in pets.

Pets can get skin cancer just like humans. Prolonged sun exposure causes sun damage and increase risks of skin cancer. Your dog or cat’s fur acts as a natural barrier against harmful UV rays. However, in very sunny places or for pets that love to be outside, their fur may not be enough. Pets can develop skin cancer on exposed areas of their body like their stomachs, tips of ears, and on the face. Skin cancer is pets is commonly seen in pets with a white- or light-colored coat. For pets that love to be outside, use and all-natural pet sunscreen to keep them protected.

It is often difficult to prove "cause and effect" when it comes to cancer. There are so many potential interactions between genes and environment influences that could lead to the development of a tumor, and ultimately, we may never be able to know exactly what caused the cancer in the first place.


How to cope when your pet has cancer?

It is important to keep in mind that pet cancer does not equate to a death sentence. Although it is true that cancer is one of the most common disease-related death in senior dogs and cats, it is also one of the most treatable diseases. Thankfully, continuous development of new treatments to fight cancer are all possible due to advancements in both human and veterinary medicine.


Are some types of cancers more treatable than others? 
All cancers are different and some are more treatable than others. The type of cancer, location, size, stage and response to treatment will affect the diagnosis and treatment. With many cancers, the earlier the treatment is started, the better the prognosis, and ultimately, the longer the survival times. That's why it is so important to bring your pet to the veterinarian for examinations at least once a year. 

Always consult your veterinarian when it comes to your pet’s health. Your veterinarian can more accurately assess your pet’s health by completing a physical exam, reviewing the medical history, and having an in-depth conversation with you about any changes in behavior, diet, exercise, and other factors.