Cat Sunbathing
Good owners are always looking for ways to prevent, avoid or minimize illness in their pets, and cancer would be at the top of any list of potential concerns. What causes cancer in pets? What risks can be avoided?

The American Cancer Society estimates that 10 to 15 percent of all human cancers are caused by viruses. It estimates that hereditary cancers occur even less often. But how do these statistics translate over to the veterinary world? What do we know about the causes of the many manifestations of this disease in pets? 

The truth is, our knowledge about cancer in pets lags behind the body of knowledge that exists about cancer in humans. This is due in part to the lack of requirements for pet cancers to be logged into a centralized cancer registry as there is in human medicine. Without a similar animal cancer registry in veterinary oncology, we cannot know how many cases of cancer actually occur in dogs and cats, what types and where. In my state, New York, for example, all human cancer diagnoses are reported to the New York State Health Department, and data on demographics and death rates are available for review study.

Even without an animal cancer registry, however, we veterinary oncologists do know the causes of at least some cancers in animals. Let’s take a brief look at our known list of culprits.

Is Cancer an Infection?

A recent publication in Emerging Infectious Diseases linked brain tumors in California raccoons to infection with a newly discovered polyoma virus. Cancer is rare in raccoons, and when wildlife biologists identified several similarly affected raccoons, they began to investigate the cause. 

Viruses are well known to cause cancer. Cervical cancer in women is a prime example of a viral cancer. A sexually transmitted papilloma virus is known to be the cause, and now a vaccine administered to adolescents can prevent infection with the virus and the resulting cancer. The equine papilloma virus has recently been implicated as the cause of genital cancer in horses.

Prior to the introduction of a vaccine against feline leukemia virus, lymphoma was a common and fatal diagnosis in young cats. Feline leukemia virus turns on genes that cause unregulated cellular growth, which is simply another name for cancer. Reportedly, Kim Kardashian’s Persian kitten died of this terrible disease. A similar virus, bovine leukemia virus, is found in cattle and causes lymphoma in this species as well.

Sadly, the Tasmanian devil, which is only found in the Tasmanian state of Australia, is currently threatened with extinction by a contagious cancer. Devil facial tumor disease spreads as a result of the aggressive biting behavior of devils, and no vaccine has yet been developed to protect these carnivorous marsupials.

Solar-Induced Skin Cancers

We wear sunscreen, hats with wide brims and protective clothing when we enjoy the outdoors. We are protecting ourselves against wrinkles in our old age and, more important, skin cancer. Sunbathing dogs, outdoor cats with white ears and noses, and horses with pink skin on their face and head are all at risk for sun-induced tumors.

If you have one of these at-risk pets, keep them out of the sun and provide sun protection by keeping them indoors or using protective gear. Any red, ulcerated or scabby skin should be examined and biopsied by your veterinarian.

The Risk Is in Their Genes

Although hereditary cancer is uncommon in humans, some mutations leading to cancer are well known, such as those in the BRCA 1 and 2 genes linked to breast and ovarian cancer.

Using the cloned canine genome, veterinary researchers are ferreting out the genetics of certain canine cancers.

The close genetic relationship between members of certain dog breeds seems to be a predisposing cause of some types of cancer. According to the Golden Retriever health survey, the major cause of death in this breed is cancer, predominantly lymphoma and hemangiosarcoma.

Lymphoma in dogs carries similar genetic abnormalities to that of lymphoma in humans, and determining the genetic makeup of lymphoma in dogs can help predict the subgroup of lymphoma and thus the prognosis for individual dogs.

Environmental Carcinogens

Human behavior affects our risk of developing cancer. Tobacco use, alcohol consumption, lack of exercise and a poor diet are risk factors for developing cancer. We take better care of our pets than we do of ourselves, and these are not typically risk factors for animal cancers. The exception, however, is exposure to environmental tobacco smoke, which has been associated with oral squamous cell carcinoma and lymphoma.

Additionally, increased exposure to environmental dusts is also associated with an increased risk of lung cancer in dogs, and an increased incidence of lymphoma has been associated with environmental contamination with toxic waste.

Finally, when your lawn is treated to prevent unsightly weeds, it may cause a problem in your dog. Preliminary research has shown that Scottish Terriers, a breed at risk for bladder cancer, may have a greater risk of developing this deadly tumor when exposed to herbicides applied to your lawn. To be safe, it’s best to keep everyone off the lawn for the time recommended by your lawn specialist.

Knowing the Cause Allows Prevention

The bottom line is that you can impact your pet’s cancer risk by adopting a few simple strategies.

  1. Keep your pet out of the sun, especially between the hours of 10 a.m. and 2 p.m.
  2. Prevent infection with feline leukemia virus by keeping your cat indoors and by administering the feline leukemia vaccine.
  3. Don’t smoke. This is good for you and your pets.
  4. If you live in an area of high environmental pollution, keep your windows closed, use air purifiers and filter your water.
  5. Research your breed before getting a new pet.
Cancer is an unpredictable disease, but it can’t hurt to try and minimize risk wherever you can.

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