Conscious Choice: Why is Cancer Killing Our Pets?

November 2000

Why is Cancer Killing Our Pets?

by Deborah Straw

Last weekend I traveled to Portland, Maine, with a couple visiting from Greece. Newlyweds in their early forties, they do not plan to have children. Trying to find a common bond, I asked the man if they had any animals. He said, "No. I had a dog when I was a child and then he died. Of course, it’s natural. But it was so terrible. I couldn’t live through that again."

I know how terrible the death of a pet is. In the past fifteen years four of our five domestic animals — three cats and a dog — have died of cancer or a related illness. One cat, Annie, died of feline leukemia (not considered a cancer in pets, but often associated with a secondary cancerous disorder or lymphoma) at eighteen; another, Misty, of mammary cancer, also at eighteen. Our dog Bauhaus died of a mast cell tumor in her neck at twelve, and the fourth pet, Puck, an eight-year-old cat, died of a vaccine-induced fibrosarcoma.

While caring for our own ill animals, my resolve to take action grew stronger. As our animals continued to get sick, we made every effort we could to be certain we were providing the best and safest care for them. We had a tap water test done to check for lead; it came back negative. We don’t smoke or use pesticides. We made dietary changes for our subsequent cats and dog. We no longer bought them any grocery store commercial foods, purchasing instead only high quality "natural" foods at pet stores. I decided to do some research to see if other people were experiencing as many painful deaths as we were. I discovered that many people we knew had similar cancer stories to tell, although perhaps not so many in rapid succession. After looking for resources to learn more about cancer in animals and its prevention and treatment, and finding few available, I decided to write one. I determined to do everything I could to help other animals and their human companions avoid this pernicious disease, to diagnose it earlier, or to provide a better chance for survival after diagnosis.

According to an October 1997 Morris Animal Foundation survey, cancer is the number one killer of dogs and cats, and the number one concern of pet owners. At least 25 percent of dogs and cats die from cancer; in some veterinary practices, 40 percent of the patients have some form of cancer. In the Morris study, which surveyed 2,003 pet owners, the leading cause of nonaccidental death in dogs was cancer (at 47 percent). In cats the three leading nonaccidental causes of death are dental problems, urinary problems, and cancer, the last at 32 percent. That survey also identified cancer as the leading cause of disease-related deaths in ferrets (33 percent), rabbits (28 percent), and birds (18 percent). Other studies indicate that 45 percent of dogs over ten years of age die of cancer. Some seventy types of cancer have been identified in domestic animals.

Incidence of Cancer

In the United States cancer now afflicts 1 in approximately 3.5 adults aged sixty to seventy-nine and 1 in 55 before the age of thirty-nine. It is the number two killer of humans, after cardiovascular disease. In fact, cancer’s rise in occurrence came first among humans, but pets are no longer far behind. Some other species can get almost as many kinds of cancer as we can. No breed-specific genetic alterations have been found that predispose certain breeds to develop cancers, but some breeds do acquire the disease a bit more commonly than others. Among cats, for example, there is a high incidence of cancers in the Siamese breed.

Some of the factors involved in the development of cancer in our domestic animals mirror those involved in human cancer. Others seem much more specific to animal cancer than to the disease in humans. Let me stress that there seems to be no agreement about what exactly causes cancer in animals — this is an extremely complex disease with many varieties. Some veterinarians say it is entirely genetic; some think diet and lifestyle issues are key. Some believe it is mostly a function of increased age. According to the veterinarians at Hill’s Pet Food, animals are living longer for many reasons, including a decline in often fatal infectious diseases, more effective drugs, improved diagnostics and technology, and better-educated and more committed pet owners. Pets are now, in most countries, recognized members of society and families and, as such, receive better health care and improved nutrition, leading to longer lives.

Common Cancers in Animals, Especially in Dogs and Cats

The All-Care Animal Referral Center in California lists seven varieties of common cancers found in companion animals. The American Veterinary Medical Association adds a few others to this list.

• Abdominal Tumors: These are quite common but difficult to diagnose early on. Abdominal enlargement and weight loss are signs of these types of tumors.

• Bone Tumors: These are quite common in large dogs but rare in cats. The leg bones near the joints are the most common sites for these tumors. Lameness or swelling of the leg are early warning signs.

• Brain Tumors: These may occur in both dogs and cats as primary or metastatic tumors.

• Canine Mammary Tumors: These are the most common tumors found in female dogs, generally those that are older. If a dog is spayed prior to her second heat cycle, the risk decreases. Approximately half of all mammary canine tumors are malignant.

• Feline Mammary Tumors: These are generally seen in older female cats; our cat Misty was about eighteen when her tumors appeared. They tend to grow and metastasize rapidly. According to the American Veterinary Medicine Association, 50 percent of breast tumors in dogs and 85 percent in cats are malignant. Spaying or neutering at an early age greatly reduces the risk.

• Head, Nose, and Neck Cancers: Mouth cancer is common in dogs, but less so in cats. Because many of these swellings are malignant, early treatment is critical. Masses on the gums, bleeding, odor, or difficulty eating are warning signs. Nasal cancers may occur in both cats and dogs. Signs are bleeding from the nose, labored breathing, or facial swelling.

• Lymphosarcomas: This is a cancer of the lymphatic system that occurs mostly in middle-aged animals (in cats, around eight to ten years; in dogs, around six to eight years).

• Mast Cell Tumors of the Skin: These are skin tumors seen in middle-aged and old dogs and in older cats. These tumors metastasize to lymph nodes. Our mixed-breed (yellow Lab type) dog, Bauhaus, developed this cancer in her neck at the age of eleven.

• Melanomas: These are skin cancers. They are usually solitary, black-pigmented tumors, either benign or malignant, and hard to control. Most skin cancers in cats are malignant; in dogs, they often are benign.

• Osteosarcomas: These are bone cancers most often seen in large breeds of dogs. The tumors metastasize quickly.

• Testicular Tumors: Tumors on the testicles are rare in cats, but common in dogs. They show up particularly in those with retained testes.

Warning Signs of Cancer

As is true with any behavioral or physical change in your companion animal, warning signs of tumors both benign and malignant should be checked out thoroughly and immediately by your trusted veterinarian. All experts in the animal health field say that early detection and prompt diagnosis and treatment of cancer will increase the chances of recovery, or at least of a longer, happier life for the animal.

Here are what the majority of veterinary sources consider as the possible symptoms of cancer:

• Any abnormal swelling or lump that keeps growing.

• Nonhealing sores.

• Weight loss for no apparent reason.

• Loss of normal appetite.

• Bleeding or unusual discharge from a body opening such as the nose or mouth

• A foul odor, especially from the mouth.

• Difficulty eating or swallowing.

• Loss of strength and disinterest in normal exercise.

• Lameness or stiffness that continues.

• Difficulty breathing, defecating, or urinating.

• Any other change in behavior. For example, according to the University of Pennsylvania Cancer Center’s OncoLink Web site, some case studies regarding bone cancers indicated that the dog or cat first started limping.

Prevention and Early Detection

Prevention and early detection can make all the difference. Marion S. Lane and the staff of the Humane Society of the United States write, in Complete Guide to Dog Care, that "your best offense in protecting your [pet] against serious illness is a good defense" — including regular visits to your veterinary doctor; spaying or neutering, which helps prevent diseases of the reproductive organs as well as overpopulation and abandonment of pets; screening exams that your veterinarian recommends, especially as your animal ages; and careful observation and prompt investigation of "anything out of the ordinary." And according to Steven E. Crow, D.V.M., malignant tumors identified during regular exams are more likely to be cured "than cancers which are already causing clinical signs of illnesses."

Crow, head oncologist at the Sacramento Animal Medical Group, Sacramento, California, adds that the likelihood of many animal cancers can be significantly reduced in at least three ways:

• Spaying female dogs prior to their first heat. This reduces the risk of breast cancer to 0.5 percent. An ovariohysterectomy after one heat cycle or two or more estrous cycles reduces the risk of mammary carcinomas to 8 or 26 percent, respectively.

• Neutering male dogs eliminates all testicular tumors and decreases the possibility of circumanal adenomas and adenocarcinomas.

• People with white or light-pigmented cats should minimize their pets’ exposure to sunlight — especially between 10:00 am and 4:00 pm — to protect against squamous cell carcinomas of the eyelids, nose, and ears; owners of white dogs can use sunscreens (up to SPF 30) and avoid excessive sun exposure. This may reduce the prevalence of solar-induced cancers, such as basal cell carcinomas and squamous cell carcinomas, on these dogs’ noses.

With dogs, watch for growths in the mouth and on the dog’s body. Check each mammary gland periodically, approximately once a month. With male dogs, especially those older than six years, palpate the testicles to see changes in size that could indicate a growth, notes Terri McGinnis, D.V.M., in her book, The Well Dog Book: The Classic Comprehensive Handbook of Dog Care.

Here are a few more tips, especially important for all older pets:

• Make annual medical checkups. Geriatric animals should be checked at least twice a year. (For small animals, or those who get especially nervous and anxious before and during trips to the vet, it is wonderful if you can find a veterinarian who makes home visits.)

• Keep your animal on a well-balanced, nutritious diet.

• Try not to needlessly alter your animal’s routines. Changes can bring on stress. Try to feed and walk at regularly scheduled times.

• Before bringing in a new pet, consider your older pet’s reactions. Many older dogs and cats enjoy younger ones, while some do not. You can create misery, and possibly even illness, if you force a new roommate on a set-in-her-ways animal.

• Keep your pets clean. They like it, and they feel nicer to your touch.

• Touch your animals regularly to establish closeness and to detect any early lumps or abnormalities. This is an important part of the human-animal bond.

• Keep the water dish washed and full of clean water.

• Play with your animals on a regular basis. It’s good for both of you.

Dealing with Cancer

In traditional Western medicine, of course, doctors and nurses treat symptoms with a variety of techniques that have been proved to work, fully or at least partially, for varying lengths of time. In the case of cancer, surgery, chemotherapy, radiation, changes in diet, and other medications are among them. But holistic practitioners tend to look at the whole person or animal and make larger lifestyle changes — before disease strikes, if possible. Indeed, many experts believe that in both people and in animals, the best ways to treat cancer — to lessen its risks — are prevention and early detection.

Marion S. Lane and the staff of the Humane Society of the United States say it quite succinctly in Complete Guide to Dog Care: "There seems to be more evidence every day that we humans can help prevent disease and disability by exercising, eating well, and managing the stress in our lives. The same is true for our dogs [and cats, ferrets, and so forth], but in their case, we’re the ones who are in control of their diet, their exercise, and their lifestyle...just start thinking about the fact that your focus on prevention can have a big impact on your dog’s health and welfare."

As Rachel Carson, author of Silent Spring, wrote in 1962: "Today we find our world filled with cancer-producing agents. An attack on cancer that is concentrated wholly or even largely on therapeutic measures...will fail because it leaves untouched the great reservoirs of carcinogenic agents which would continue to claim new victims faster than the as yet elusive‘cure’ could allay the disease." She quotes W. C. Hueper, who said that "the goal of curing the victims of cancer is more exciting, more tangible, more glamorous and rewarding than prevention."

These attitudes about "curing" still seem to abound even as the numbers of the sick climb. Much progress has been made, of course, with humans and now with domestic animals. But our world has more carcinogens, and many of us spend less time on diet or on exercise for ourselves and our pets as we hurry, hurry, hurry to meet the increasing number of demands on our time.

As Carson also wrote, "For those in whom cancer is already a hidden or a visible presence, efforts to find cures must of course continue. But for those not yet touched by the disease and certainly for the generations as yet unborn, prevention is the imperative need."

Excerpted with permission from the book Why Is Cancer Killing Our Pets?: How You Can Protect and Treat Your Animal Companion by Deborah Straw, published by Healing Arts Press, an imprint of Inner Traditions International, Rochester, VT 05767 Copyright © 2000 Deborah Straw. To order, call: 800-246-8648. .

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