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

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Not All Tumors Are Created Equal


Pet Column for the week of January 9, 2006


Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
Kim Marie Labak
Information Specialist

Tumors, or abnormal growth of tissue, are common in pets, but tumors can vary from a benign, fatty lump on the skin to a malignant lymph node cancer that can spread throughout the body.

According to Dr. Lorin Hillman, veterinary oncology resident at the University of Illinois Veterinary Teaching Hospital in Urbana, many tumors are very treatable.

One type of abnormal growth is hyperplasia, which is the production of too many normal cells, causing enlargement of an organ. Hyperplasias are benign, meaning that they do not invade or spread to other tissues, but they can cause health problems in other ways. For example, hyperplasia of the prostate in dogs can cause urinary obstruction by pressing on the adjacent urethra.

Thyroid hyperplasia in older cats can cause overproduction of thyroid hormone, which regulates metabolism. Excess of this hormone can increase a cat's metabolic rate, causing them to be hyperactive and very thin despite an insatiable appetite.

Lipomas are benign tumors of fat cells common in aging dogs and typically present as fatty lumps under the skin. In horses, mushroom-shaped lipomas can form in the abdominal cavity and entrap segments of intestines, requiring surgery.

Cancerous tumors develop when normal cells are changed genetically so they grow uncontrollably. Damage to cell DNA can lead to development of cancer cells. Cells have several mechanisms to protect their DNA from damage, but excessive exposure to DNA-damaging chemicals or radiation can overwhelm these protections.

Also, certain purebred animals inherit defects in these protection mechanisms, increasing their risk for cancer. The risk for developing cancer increases with age, and since pets are living longer these days, veterinarians are seeing more cases of cancer in pets.

"It's very important that pet owners understand that there are many different kinds of cancer," says Dr. Hillman. "A diagnosis of cancer does not always come with a poor prognosis."

Benign and malignant tumors can display very different behavior. More malignant cancers can spread to other parts of the body through blood, lymph or spinal fluid.

Cancer can affect any part of the body. Different types of cancers arise from different types of cells, and each type of cancer can vary in its behavior. "Some types of cancer are very slow to develop and grow, while others grow very rapidly," explains Dr. Hillman. Some types of cancers can cause specific problems.

Also, the location and cell type can determine the severity of cancer. Melanomas are usually benign when cutaneous (on external haired skin), but malignant when in the mouth.

Epulis tumors, tumors of the gingiva, are common dental tumors. Although dental tumors don't metastasize, they can invade local tissue, causing discomfort and interfering with an animal's eating, drinking, and grooming habits, and can require surgical removal.

Other common cancers of dogs and cats include lymphoma, bone cancer, oral cancer, mammary cancer, and cancer of abdominal organs such as the spleen or bladder.

When a tumor is found or suspected, a veterinarian may take a sample of cells with a needle for examination under a microscope. If a veterinarian suspects tumors that are not outwardly visible, such as tumors within the chest or abdominal cavity, he or she may take x-rays or use ultrasound to look for abnormalities. If abnormalities are found, he or she may perform a biopsy by surgically removing a small piece of suspect tissue and send the sample to a veterinary pathologist for examination.

Veterinarians have different ways to categorize cancers based on types of cells involved, types of changes in cells, and aggressiveness. Dr. Hillman explains, "Some types of cancer can go into remissionit varies from case to case."

"A diagnosis of cancer can be very scary and conjure up many negative images," she points out, "but owners should know that in many cases some type of treatment to help the pet is within reach." She recommends owners of a pet with cancer at least discuss treatment options with an oncology specialist, since treatment options can be tailored to fit the needs of the pet and the financial abilities of the owner.

When considering treatment options for a pet, it's important to understand that cancer therapies are used less aggressively in animals than in humans to minimize side effects and ensure that the pet has an enjoyable quality of life.

"Of course, catching cancer early gives us the best chance to successfully treat the cancer," say Dr. Hillman, "but cancer does not always present as a lump or bump and can be hard to find." Signs of cancer or other tumors within the body include lethargy, hair loss, loss of appetite, weight loss, and change in behavior.

Dr. Hillman recommends regular veterinary exams at least once a year, or twice a year as pets get older. Any lumps or bumps on an animal should be examined by veterinarian.

For more information about cancer and other types of tumors, consult your veterinarian. To find an oncology specialist in your area, visit the web site of the American College of Veterinary Internal Medicine at www.acvim.org and click on "Pet Owners and Public."