Published: November 07, 2006 01:55 pm      

Cancer risks for dogs are similar to that of humans

EDMOND — It seems the frequency of diagnosing cancer is increasing in both us and our pets. A national statistic tells us that one-half of all dogs older than the age of 10 years will be diagnosed with some form of cancer. Cancer is cancer whether it is in a human or a beloved pet.

There are several similarities between human and canine or feline cancers. In fact, much of the research being done today is done by observing dogs or cats and applying this information to human cancers.

Breast cancer is known to be associated with estrogen levels in a high percentage of patients.

In dogs for example, if they are spayed before they ever come in heat, their incidence of breast cancer is less than 1 percent. If they are allowed to cycle one time, the incidence jumps to almost 20 percent. If they are allowed to cycle two or more times, the incidence jumps to almost 50 percent.

This makes a good argument for the effects of estrogen on the mammary tissue. Every time they cycle, whether or not they have puppies, the estrogen is what drives the cycle. In this case, less is certainly better. Similar statistics hold true for cats. Early spaying has many other benefits, but this may be one of the most important in elderly pets.

Bone cancer is another aggressive tumor that can certainly put a damper on a healthy dog, especially large-breed dogs. More than 90 percent of all bone cancers are osteosarcomas.

Osteosarcomas are primary bone tumors, which means they originate in the bone. These tumors are highly malignant meaning they are aggressive and metastasize quickly to other parts of the body. The main sites of metastasis are other bones and the lungs.

Why large breed dogs such as greyhounds, great Danes, malamutes and Saint Bernards are affected more than small-breed dogs is not yet understood. Genetics certainly may have a role to play in this, but possibly also the rapid growth of long, large bones may offer a breeding ground for abnormal cells and eventually cancer.

Unfortunately, there are few warning signs for osteosarcoma until it is well-advanced. Presenting signs include lameness, swelling or a subtle limp. An X-ray of the lungs prior to treatment is essential since this is a favorite spot for metastases.

The most common treatment is amputation of the affected limb along with chemotherapy. The average survival time is one year after amputation.

Radiation therapy is coming of age for pets and it may lengthen the survival time when combined with chemotherapy or even done alone. There are referral centers in our area that specialize in treating dogs and cats with radiation therapy.

The decision to amputate is a good one for the quality of life of the pet.

Amputation combined with chemotherapy increase survival time even longer, and allows quality of life to be extended. Obviously a longer life with a poor quality of life is not acceptable.

The simple fact that our pets, like us, are living longer, certainly ups their risk of getting some kind of cancer before they die.

Humans who live to 75 years of age have a 38 percent chance of getting cancer. Dogs have a 35-40 percent chance of getting cancer, usually after 7-8 years of age.

Today many of our pets are living to well in their teens and some into their 20s. This alone will increase the incidence of cancer.

As with humans, early detection and treatment sometimes can be curative.

Check your pet frequently for tenderness on long bones, enlarged lymph nodes — ask your veterinarian to show you where they are — and for consistent urination/defecation, i.e. not straining to go. Changes in eating habits, vomiting and abnormal bleeding from the mouth, stool or urinary tract should signal an immediate visit to your veterinarian.

Remember, early detection is the key.

(Dr. M. Margaret King, a longtime Edmond veterinarian, is a guest columnist. If you have any questions for her, send them to 1900 S. Bryant, Edmond, OK 73013.)