Pet Columns, Office of Public Engagement, College of Veterinary Medicine at the University of Illinois at Urbana-Champaign

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Cancer Risks in Cats and Dogs


Pet Column for the week of January 19, 1998


Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
By Theresa A. Fuess, Ph.D.
Information Specialist

"Most people are familiar with environmental risk factors for cancer in people," notes Dr.
Barbara E. Kitchell, oncologist and veterinarian at the University of Illinois Veterinary
Medicine Teaching Hospital at Urbana. "Pet owners should also be aware of the risk
factors for cancer in their pets."

Spaying and neutering can reduce the risk of cancer. Dogs spayed before the first heat
cycle have only half the risk of mammary carcinoma of those spayed after the first but
before the second heat cycle. Dogs spayed after the fifth heat cycle or never spayed have
the highest risk of mammary cancer. Testicular carcinomas or tumors in dogs are common,
but having your dog neutered eliminates that risk. Fortunately, testicular cancer rarely
spreads in dogs, unlike in human beings, so treatment has a high success rate.

As in humans, animals that receive excessive exposure to sunlight are at risk for skin
cancers, but only in animals or areas without hair or pigmentation. For cats, risk areas
include the pink tip of the nose, the eyelids, and areas around the ears. For dogs the risk is
associated with a fair complexion and exposure to the underbelly or inside of the back legs.
In high mountain areas where ultraviolet light is particularly strong, skin cancer often affects
pointers, bull terriers, pit bulls, and Dalmatians. "In Dalmatians," says Dr. Kitchell, "the
cancer will circle around a black spot and won't enter the black skin."

Dogs have a much higher incidence of nasal sinus cancer than do people. "This may be
because they have more nose to get cancer in and because their noses are always on the
ground sniffing up chemicals and other carcinogens that concentrate there," says Dr.
Kitchell. Carcinogens range from herbicides and pesticides for dogs in rural areas to factory
or automobile pollution for urban dogs.

The mouth is the fourth most common site of cancer in domestic animals. It may be that
mouth cancers arise at such high frequencies in dogs and cats because carcinogens from the
air land on their coats and get into their oral tissues when they groom them-selves. Breeds
with dark pigment in the mouth, such as German shepherds, black cocker spaniels,
Scotties, and chows, are prone to melanoma in the mouth. Swelling around a tooth when
there is no tooth injury or dental disease could be a sign of mouth cancer.

Other breeds that are more susceptible to certain cancers include Siamese cats, which tend
to get a variety of cancers, such as salivary carcinomas and intestinal carcinomas, at a
younger age than others breeds. Mast cell tumors (in the connective tissue) are often seen in
British short nose breeds, such as boxers, bull dogs, and Boston terriers, although any
breed can get mast cell disease. Older giant or large-breed dogs are predisposed to bone
cancers at the ends of long bones. These may result from tiny stress fractures that occur
during the rambunctious puppy stage. Before you acquire a large-breed dog, it is important
to ask the breeder if there has been cancer in their lines.

In any pet, the site of an injury or other trauma may later develop cancer. It is known, for
example, that cats sometimes develop sarcomas at vaccination sites. A dog or cat may also
develop sarcoma at sites of old bone fractures, especially those associated with chronic
non-healing or with loose implants such as a metal plate or pin. If your animal becomes
lame later in life, cancer may have developed at the fracture site. Chronic inflammation is
also associated with cancer. Cocker spaniels with chronic ear infections sometimes develop
carcinoma in the cerumin gland, the wax-producing gland.

Pets are protected against common "people" cancers of the gastrointestinal tract and lungs
because pets generally eat a high-fiber, low-fat diet and do not smoke.

"Many aspects of cancer are the same for people and for animals," says Dr. Kitchell. "For
instance, cancer is typically a disease of aging. In cats and dogs, the peak incidence occurs
at 10 to 12 years of age. For both people and animals, the sooner cancer is detected and
treated, the better the chance the patient can be cured." For this reason, a geriatric checkup
every six months is good idea for older animals.

To catch the disease in the early stages, pet owners need to be alert to changes in their pet's
behavior. Watch for rapid loss of weight; change in elimination habits; decreased energy
level; physical symptoms, such as sneezing or coughing; changes in the shape, texture, or
size of a wart or a mole; or a change in behavior patterns. Changes could be gradual or
sudden.

Dr. Kitchell advises owners to be observant. Both cats and dogs may hide symptoms. For
cats, it seems to be a natural protective behavior not to let bigger animals know that they
are sick. Dogs may continue to do things they don't feel well enough to do because they
want to please their owner.

For more information about pets and cancer, contact your local veterinarian.