Cancer: pet guardians fear this diagnosis above all others; not only because the conventional treatments are so perilous, but also because, despite treatment, it is most often fatal. More than half of dogs over the age of 10 will die of cancer, and the incidence of cancer in cats and younger animals is growing rapidly. As responsible guardians, we need to understand the risk factors that contribute to the development of cancer; do all we can to prevent it; and take effective action when a diagnosis of cancer is made.

Causes of Cancer in Pets  

Our modern world has many conveniences, but also many hazards that simply didn't exist a few generations ago. For example, many carcinogens (cancer-causing compounds) are now ubiquitous in air and water.

Cancer develops due to a variety of factors, many of which we cannot control. No one knows exactly what causes most cancers, but it is most likely a combination of one or more of the following factors, along with a genetic predisposition or sensitivity that makes a particular dog or cat susceptible to cancer (more detailed discussions can be found below the list):

General Factors

• Age (older animals are more prone to develop cancer)
• Breed (e.g., Boxers and Golden Retrievers are prone to develop lymphoma; giant breed dogs are more apt to develop bone cancer)
• Genetic mutations
• Over-vaccination (especially with killed vaccines, which contain toxic adjuvants such as mercury and aluminum)
• Pharmaceuticals
• Retroviruses (in cats)
• Chronic inflammation
• Oxidative cellular damage
• Obesity
• Stress

Environmental Toxins

• Cleaning products
• EMFs  (electromagnetic fields) and other sources of radiation, including sunlight
• Chemical emissions (e.g., flame retardants and plastics from computers, flooring, clothing, furniture, carpets)
• Air pollution - outdoor and indoor
• Pesticides and other chemicals
• Air fresheners
• Second-hand smoke (in cats and long-nosed dogs, such as collies and greyhounds)

How serious are environmental toxins? A recent report by the Environmental Working Group found 48 chemicals in pets' blood (out of 70 tested for); 43 of them reached levels far higher than in people: 5 times as much mercury; 2-1/2 times more perfluoro­chemicals in dogs (from stain- and grease-proof coatings), and 23 times more fire retardants in cats.   

Food toxins

Many pets ingest a host of toxins through their everyday diet. Here are just a few of the potential toxins in commercial pet food: 

• Acrylamides, trans fats, and other carcinogenic factors used or created during the manufacturing of dry kibble.
• Chemicals in food and treat packaging, such as BPA and other plastics.
• Bacteria are present on virtually all dry pet foods; some, like Salmonella, produce their own toxins and can make pets very ill.
• Contamination with chemical fumigants applied during storage and transportation.
• Genetically modified (GMO) ingredients (94% of soy; 70% of corn; 74% of cottonseed oil; 80% of canola oil in the U.S. are GMO). GMOs damage the primary detoxification organs (liver and kidneys).
• Persistent Organic Pollutants (POPs) are persistent and ubiquitous around the world; they are linked to several human cancers. POPs are found in fish, animal fats, and other animal products used in pet food.
• Antibiotics and other drugs are used in livestock, and may persist throughout pet food processing.
• Crops condemned for human consumption due to excessive pesticide or fertilizer residue may be used without limit in pet food.
• Molds and mold toxins are common contaminants of corn and other grains. At least one of these, Aflatoxin B1, is known to cause liver cancer.
• 27 categories of "food enhancers" are allowed in pet food, including preservatives, texturizers, colorants, emulsifiers, binders, stabilizers, thickeners, surfactants, and lubricants.

How can you tell if your pet has cancer? Many cancers are difficult to detect early. Most cancers will not show up on blood tests. But there are some signs to look for, especially in older pets.

1. New or changing lumps or bumps. Most skin tumors in dogs are benign, while in cats the opposite is true. But even your veterinarian can't tell just by looking or feeling.  Your dog may have a dozen lipomas (benign fatty tumors), but the next one could be different. Any new lump, or one that is changing or growing, should be either aspirated or biopsied to make sure it's not cancer.

2. Weight loss not related to diet. Obesity is a huge problem in pets, and if your pet is losing weight because you are feeding or exercising her differently, that's a good thing! But weight loss for no apparent reason is a hallmark of cancer, although it can also signify conditions like diabetes or kidney disease. Regardless, a visit to the veterinarian is in order.

3. Changes in activity level, behavior, or temperament; e.g., getting grumpier in general, becoming reluctant to move, not wanting to be handled or held, or withdrawing from normal activities or social interactions.

4. Changes is urination or defection. If you notice blood or mucus in the stool or urine; or if your pet is straining or develops diarrhea or constipation, your veterinarian needs to investigate whether cancer could be the cause.

5. Non-healing wounds. Sores, wounds, or rashes that never seem to heal can be a sign of skin cancer. A scrape, aspiration, or biopsy should be performed.

6. New or excessive drooling. Dental disease is a common cause of excessive salivation, but it can also be caused by tumors in the mouth, which are probably more common than you think. A tumor in the back of the mouth or throat can also cause difficulty in swallowing.

7. Bloating (abdominal distention). If your pet gradually seems to be getting bigger around the middle (as distinguished from sudden bloating caused by twisting of the stomach in deep-chested dogs), the reason could be a growing tumor. Radiographs (x-rays) or abdominal ultrasound can help find the cause.

8. Changes in breathing. Rough-sounding or faster breathing may indicate tumor(s) in the chest. Many kinds of tumors will metastasize to the lungs, so this is something that needs to be checked out immediately. In cats, a respiratory rate (breaths per minute) over 30 needs veterinary attention.

Holistic veterinarian and author Dr. Jean has 18 years' experience in conventional and alternative veterinary medicine. She has a passion for feline health and nutrition; she has intensively studied and researched pet nutrition and the pet food industry since the early 1990s. She is recognized as an expert on pet food, having written dozens of articles and been interviewed for print, radio, and television around the world.  In 1995, she founded Spirit Essences (now owned and operated by Jackson Galaxy), which makes flower essence remedies for many animal health and behavior problems.For more information about Dr. Hofve, please visit LittleBigCat.com.

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