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Cancer is one of the most important causes of illness and death in cats although cats develop cancer only half as often as dogs. Unfortunately, a cat’s chances of developing cancer increase with age. Why cancer develops at all, and why it is seen more commonly in older animals, is not well understood. Many factors, including genetic and environmental ones, have been identified as potential causes. However, cancer is a general term used to encompass many different diseases, and each disease may well have its own causative factors. Some of these factors are known, but in most cases, the cause of an individual cat’s cancer is not. Fortunately, cancers in cats and dogs often have counterparts in humans so that cancer research tends to benefit both our pets and us.

Some feline cancers are associated with viral infections, particularly feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV). Cats infected with FeLV have a greater than 60 times increase in their risk of developing lymphoma. FIV has been associated with some cancers as well. One way to decrease the risk of cancer in cats, therefore, is to protect against infection with these two viruses. Other specific ways to decrease the risk of some cancers also exist. For instance, avoiding exposure to strong sunlight reduces the risk of squamous cell carcinoma of the skin in white cats and early spaying reduces the risk of mammary cancer for all female cats.

Regardless of the type of cancer a cat may have, the disease usually causes common clinical signs. These may include lethargy, poor appetite, depression and weight loss. Sometimes the presence of a possible cancer is obvious (such as a skin mass) but in many cases, it is not. Veterinarians rely on a good physical examination plus diagnostic testing to pinpoint the cause of a cat’s illness. Screening tests for specific types of cancer are yet to be developed for veterinary medicine. When evaluating a cat that may have cancer, it is important not only to get a definitive diagnosis of the type of cancer, but also to evaluate the cat’s overall health status. Many elderly cats have more than one disease process present.

The Veterinary Cancer Society lists ten common signs of cancer that pet owners should be aware of:

  • Abnormal swellings that persist or continue to grow
  • Sores that do not heal
  • Weight loss
  • Loss of appetite
  • Bleeding or discharge from any body opening
  • Offensive odor
  • Difficulty eating or swallowing
  • Hesitation to exercise or loss of stamina
  • Persistent lameness or stiffness
  • Difficulty breathing, urinating, or defecating

A process called staging is also used in the evaluation of cancers. Staging determines the degree of cancer involvement in the patient. It can help determine the prognosis and suggest treatment options. There are various systems devised to stage a cancer, but they primarily rely on answering three questions:

1. How large is the primary tumor?

2. Are local lymph nodes involved (local metastasis)?

3. Are tissues distant from the primary tumor involved (distant metastasis)?

In addition to the usual blood and urine tests, some sophisticated diagnostic techniques are often available to aid in the diagnosis and staging of cancer patients. Imaging techniques such as radiology (x-rays), ultrasonography, and CT (computed tomography) scans are very useful.

For instance, CT scans are the tool of choice to image tumors of the brain and ultrasonography is the tool of choice for imaging tumors in the abdomen. Conventional x-rays are best for tumors in the chest. A veterinarian’s choice of imaging technique will also be influenced by what services are available locally.

One of the most important tools for evaluating cancer is a biopsy. This can be performed by several different methods, such as fine needle aspiration or a surgical biopsy. The type of cancer suspected and its location often dictate the type of biopsy that is performed. Biopsies of internal masses may be accomplished by using ultrasound guidance. Biopsies can help determine not only the type of cancer present, but whether it is aggressive in its behavior or not. This information is necessary to help owners and veterinarians decide which course of action is in the cat’s best interests.

The decision whether to treat a given cancer can be a difficult one. In some cases, where the prognosis is poor or the owner is not in an emotional or financial position to attempt treatment, the best option might be euthanasia. Some cancers are potentially curable; others have a poorer prognosis and may provide short or long-term survival possibilities. In every situation, the quality of life for the cat must be considered. The treatment itself may not be appropriate for some patients, even if it could provide long-term remission or a cure.

Just as for humans with cancer, various treatment options are available for cats, depending on the type of cancer and what is available locally. In many cases, cancer is still a surgically treated disease. But some cancers are most amenable to chemotherapy, or radiation, or a combination of therapies. As newer modalities, such as photodynamic therapy and immunotherapy, are established for cats, they will become more widely available. Treatment of cancer may also involve other issues, such as nutritional support and pain management.

For more information, visit the Veterinary Cancer Society.

Please Note: The Winn Feline Foundation provides the feline health information on this site as a service to the public. Diagnosis and treatment of specific conditions should always be in consultation with one's own veterinarian. The Winn Feline Foundation disclaims all warranties and liability related to the veterinary information provided on this site.

Credit: Used with permission of the Winn Feline Foundation.  Reviewed by Amy I. Attas, V.M.D.
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