9 Misconceptions About Cancer in Pets

Joanne Lynn Intile, DVM, MS, DACVIM
Updated: February 11, 2021
Published: January 03, 2017
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Common Cancer Myths

By Dr. Joanne Intile, DVM, DACVIM

Owners of pets diagnosed with cancer often use the internet to research their animal’s disease, and distinguishing fact from fiction can be a formidable task. The unfortunate truth is that for every evidence-based, accurate website centered on cancer care in animals, there are far more websites perpetuating questionable myths.
Here are some common cancer misconceptions regularly encountered by oncology vets in the exam room:

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Myth 1: Feeding a Specific Diet Can Prevent Cancer

Many owners believe that feeding their pets a specific type of diet can prevent cancer, or that feeding their cancer-stricken pets a specific diet can alter the course of cancer treatment. While it’s true that some ingredients are healthier than others, the idea that a particular diet causes or prevents cancer is false, as is the concept that feeding one specific diet will change the outcome of a pet diagnosed with cancer.

Our pets’ bodies are complex, and cancer is too, so it is an oversimplification to say that any one food on its own could have a major influence over an animal’s chance of developing cancer or on their ability to fight the disease.

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Myth 2: ‘Superfood’ Ingredients Can Prevent Cancer

Along the lines of the previous myth, some companies will market their pet foods as containing “superfoods.” These foods may contain particular fruits, vegetables or grains that have been touted as possessing special nutritive value capable of reducing risks of certain diseases, including cancer.

Cancer is a complex condition with over 100 different diseases grouped under the diagnosis of cancer. Each of these diagnoses are biologically different in terms of the cancer’s underlying genetic mutations, as well as the individual patient’s predisposition, so the claim that one food – “super” or otherwise – can cause cancer or prevent cancer is incorrect.

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Myth 3: Carbohydrates and Sugar “Feed” Cancer Cells

All sugars are carbohydrates and all carbohydrates, whether from bread or donuts, are broken down into glucose and fructose during the process of digestion. All cells, whether healthy or cancerous, use glucose as a source of energy. Tumor cells are usually replicating at a faster rate than healthy cells, therefore they have a higher metabolic demand for fuel. However, sugar doesn't make cancer grow faster. Giving more sugar to cancer cells doesn't speed their growth. Likewise, depriving cancer cells of sugar doesn't slow their growth.

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Myth 4: Vaccines Cause Cancer

The myth that vaccines cause all sorts of cancer types in dogs and cats is false. While there is an association between injections and the development of sarcoma tumors in cats and dogs, and some vaccines are given by injection, this is the only example of a relationship between vaccination and cancer development in companion animals.

Although the sarcoma tumors are most frequently associated with previous vaccination, tumors can also occur secondary to other types of injections, such as microchips, antibiotics and long-acting flea medications. We also know that cats that develop injection site sarcomas are likely to be genetically predisposed to tumor formation due to an inappropriate inflammatory reaction to the injection itself. Therefore, the injection itself is only one causal factor.

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Myth 5: Chemotherapy will Make My Pet Sick

Many owners are reluctant to pursue consultation with a veterinary oncologist due to the misconception that the treatments offered will impart significant side effects in their pets.


While chemotherapy can cause some adverse signs, they occur infrequently in veterinary patients because while the drugs we use to treat cancers in pets are the same as those used for people, we use lower dosages and space our treatments out further apart so as to minimize adverse effects.

Less than 25 percent of pets treated with chemotherapy will experience side effects from treatment, and when those effects do occur, they are typically mild and something owners can treat at home. The chance of a severe reaction that would require a visit to your veterinarian for treatment, like intractable vomiting and/or diarrhea, or inappetence for longer than one day, would be less than five percent.

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Myth 6: Treating Cancer in Pets is Too Expensive

While it is true that anti-cancer treatments such as chemotherapy, radiation therapy, or surgery can carry expensive tabs, protocols vary and veterinary oncologists will work with pet owners and their financial interests to devise optimal therapeutic plans.

When it comes to chemotherapy, it’s rare to have only one way to treat a particular tumor. More frequently, we have options that range in terms of numbers of trips to the hospital, concurrent necessary lab work or imaging tests, and route of administration, as well as cost. While price may certainly be a limiting factor for some owners, there is much value to be obtained from speaking directly with an oncologist and hearing all of the options and their associated costs rather than assuming the care is out of reach. Your veterinarian may be able to speak with an oncologist ahead of time to gain a better understanding of the range of potential fees as a means to prepare you prior to your consultation.

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Myth 7: There’s no Way the Cancer has Spread Because My Pet is Behaving Normally

I frequently recommend performing staging tests in order to examine for spread of a particular tumor or cancer type. The exact tests will depend on the diagnosis, but can include bloodwork, urinalysis, testing regional lymph nodes and imaging tests (e.g. radiographs/x-rays, ultrasounds, CT scans or MRI). The results of such tests are important, as they will influence treatment recommendations as well as a pet’s overall prognosis.


Owners are sometimes reluctant to pursue such testing, especially when their pets are showing no outward signs of illness related to their diagnosis. For example, a dog may be diagnosed with a cutaneous (skin) mast cell tumor because their owner notes a skin growth that changes in size or shape but is otherwise not bothering the pet. Mast cell tumors may remain confined to the skin or they may spread to regional lymph nodes, abdominal organs, and even to the bone marrow.

While it is true that dogs with widespread disease are more likely to be ill, not every dog with regional spread of disease (e.g., to a local lymph node) will have any adverse signs. The recommendations will be different for a dog with spread of a mast cell tumor versus one with it confined only to the skin.

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Myth 8: Mixed-Breed Dogs are Less Likely to Develop Cancer

While certain cancers occur more frequently in some dog breeds (e.g., lymphoma in golden retrievers, bladder cancer in Scottish terriers), the truth is that cancer can occur in any breed of dog. Mixed breed dogs are not necessarily at a reduced risk for disease.

Veterinarians are only beginning to understand the influence genes play in the development of cancer in dogs. Mixed breed dogs, especially those with lineages associated with known “at risk” breeds, could carry the same predispositions to cancer development as their purebred counterparts. If you are considering a particular breed of dog, or even researching a mixed breed dog, it is worth your time to have a conversation with your veterinarian about potential risks for cancer development in the future.

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Myth 9: I don’t Need to see a Veterinary Oncologist Because I’ve Done My Research on the Internet

Veterinary oncologists possess the expertise regarding the diagnosis and treatment options for cancer in companion animals and have completed four years of veterinary school, one-to-three years of internship training and three years of residency training specific to oncology. They have also passed a series of specific examinations that exhaustively cover both general internal medicine concepts and the more specific field of veterinary oncology.


Oncologists can recommend treatments known to be effective in treating a wide variety of cancers in animals. They are often the most equipped to evaluate other suggestions you may have received to determine whether they have any scientific merit, or, conversely, whether they could be an inappropriate use of your time and finances.


Facing a diagnosis of cancer in your pet is devastating. It’s natural to want to arm yourself with accurate information to make educated decisions about your animal’s care. There’s a staggering amount of information on the internet for owners to sift through. In addition to researching topics on your own, seeking a consultation with a veterinary specialist who will work alongside your primary care veterinarian is your pet’s best chance for a positive outcome.


Want to learn more about cancer in pets? Find out what to do when your dog is diagnosed with cancer.



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