Dr. Allen – Companion Animals and Cancer


Companion Animals and Cancer

We humans tend to think we’re pretty unique in the animal world, but, in fact, we are all very much alike when it comes to medical problems. Tumors and cancer are examples of conditions that affect all animals, from fish to elephants to birds.

In general, we all have potential cancer cells develop in our bodies every day. They might be mutants of normal cell division that could go wild and overproduce more cells, thereby creating a mass. Our immune systems, however, identify these abnormal cells and destroy them, or the cells naturally die off. Some animals’ immune systems may be genetically inadequate from birth, and those animals tend to have abnormal cells slip through and develop into tumors. Likewise, as we get older our immune systems are not as strong or efficient as when we were young, and again some potential tumor cells slip through our body’s screening process. Perhaps this is why lumps and bumps are more common as we get older.

Some breeds of dog seem to be more prone to tumors than others. Boxers have a reputation for being “tumor factories,” and white boxers lead their group. Labradors tend to get lipomas, but then Labradors also tend to be overweight, and I seldom see lipomas on lean dogs.

If you’ve had a companion animal for a long time, say 10 years or more, you may have noticed lumps develop, or moles or warts as the dog or cat gets up in years. Often these lumps are nothing to worry about unless they continue to grow or they are bothering the pet. Lipomas are a case in point. They are fat cell tumors; essentially a fat cell that has multiplied out of control. They can usually be felt under the skin, are round or oval, feel soft and somewhat moveable. The most common site they develop is on the side of the chest behind the front legs, but they can pop up anywhere on the body. People get lipomas, too. Lipomas are benign and need only be removed if they are getting too big (or for cosmetic appearances).

Nearly every type of cancer that people develop can also develop in our companion animals. The methods for controlling or eliminating these tumors are essentially the same for dogs and cats as it is for people. We use surgery, chemotherapy, radiation, nutrition, and everything else that works in people. There are veterinary oncologists that specialize in the latest methods for dealing with cancers. Specialty practices and veterinary schools take patients on a referral basis for diagnosis and treatment. Many veterinarians do not routinely carry the chemotherapy drugs because they are very expensive, they expire quickly, and are used infrequently.

Prognosis for certain types of cancer therapy may vary with the individual animal. Older animals may not be strong enough or have competent immune systems to battle the tumor. Other complicating factors, such as liver or kidney disease, may preclude them from treatment. In many cases, surgery is the first step if just one site is involved. If there are many tumors, both surgery and chemotherapy may be the answer. Then there are some cases in which nothing will slow or stop the progress of the cancer, as with osteosarcoma, or bone cancer.

As veterinarians, we’ve known for a long time that estrogen is connected with breast cancer. Dogs and cats that are spayed (ovariohysterectomy) before their first heat have a zero incidence of breast cancer later in life. Each year that a female animal goes unspayed increases the likelihood that lumps will develop. Dogs and cats have five pairs of mammary glands, so right away they are five times as likely as humans to develop problems. An unspayed dog is about 70% likely to develop masses in the mammary tissue when they get to be 7 plus years old. Breast cancer in our pets can be prevented through early spaying. Likewise for the males, early neutering prevents testicular cancer.

Cats can acquire all sorts of tumors and cancer, too. Injection-site sarcomas are something we see on rare occasion, and steps have already been taken by vaccine companies to avoid any future connections with injections. They usually occur over the shoulder area, where we commonly give distemper shots, and first appear as a lump that you feel, but often can’t see. Surgical removal early on may prevent spread, but they commonly return in the same area. A very small percentage of cats have been affected (a fraction of one percent), but that’s still too many if we can prevent it.

As with humans, early diagnosis is important, and if you detect a lump or mass on your dog or cat, consult your veterinarian. It may turn out to be only a sebaceous cyst, but it could be something more serious.

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