Feline lymphoma is a malignant cancer of the lymphatic system, the exquisitely structured arrangement of internal organs and tissues that directly or indirectly influences virtually every aspect of a cat’s physical existence. Unfortunately, says Margaret McEntee, DVM, a professor of oncology at Cornell University’s College of Veterinary Medicine, it is the most frequently diagnosed among all types of feline cancer.
Broadly speaking, the feline lymphatic system may be viewed as a complex network of components that transport life-sustaining substances throughout a cat’s body and help prevent the circulation of harmful agents. Among these components are the thymus gland, the spleen, bone marrow, and what veterinarians refer to as “gut-associated” lymphoid tissue, which lines the surface of various areas of a cat’s body and prevents its exposure to infectious agents.
The distinctive characteristic of the lymphatic system’s anatomy, Dr. McEntee points out, has to do with its role in transporting a life-sustaining fluid (lymph) throughout a cat’s body. Circulation of this fluid is achieved via a network of minuscule, interlaced ducts (lymphatic vessels) that connect with specialized collections of tissue called lymph nodes—tiny, bean-shaped structures situated either deeply within a cat’s body or at various areas on its surface—on the neck, in the groin, and behind the knees.
Included among the functions performed by the lymph fluid and the vessels that transport it are: delivery of oxygen and nutrients to cells; collection of metabolic waste products; absorption of fat from the intestinal tract; and the removal of tissue debris, bacteria, viruses, and other infectious agents from the body.
Lymphoma can affect the entire lymphatic system, involving lymph nodes and lymphoid cells throughout the body. When the disease centers on a cat’s lymph nodes—those deep within the body as well as the peripheral nodes—it is termed multicentric. Another type, called mediastinal lymphoma, is typically found in the chest cavity. And a third category—alimentary lymphoma—affects the gastrointestinal tract.
Decades ago, mediastinal and multicentric lymphomas were the most frequently diagnosed. However, they are closely linked to infection with the feline leukemia virus (FeLV) and, to a lesser extent, the feline immunodeficiency virus (FIV). And these viruses are less frequently seen today, presumably due to testing and isolation of infected cats and the use of vaccines that protect against FeLV. Currently, says Dr. McEntee, feline lymphoma is most often seen in the gastrointestinal tract.
Cats of any age, she notes, can get lymphoma, although most affected animals are 10 to 12 years of age. Unvaccinated outdoor cats are at greater risk than indoor cats due to their greater exposure to FeLV infection. And recent studies have indicated that cats routinely exposed to tobacco smoke are at elevated risk for gastrointestinal lymphoma.
Depending on which type of lymphoma is present, the initial signs will range from such problems as weight loss, poor appetite, and lethargy, to discernible abnormalities in lymph nodes situated in the chest or digestive tract. If lymphoma is suspected, the ailing animal will undergo a thorough physical examination designed to either confirm or exclude a tentative diagnosis of the disease. This will include complete blood cell count, blood chemistry panel, and urinalysis, plus chest x-rays, microscopic analysis of lymph node tissue samples, and ultrasound examination of an animal’s abdomen to see whether its liver or spleen—common sites for lymphoma involvement—is enlarged.
Treatment for a cat that has been diagnosed with lymphoma relies primarily on chemotherapy; in some instances, an affected animal may undergo surgery for the removal of a mass in the abdomen, and radiation therapy is used in select cases.
In general, says Dr. McEntee, “We don’t usually think of feline lymphoma as a curable condition. With chemotherapy, which many cats are on for the remainder of their lives, survival time will typically be on the order of six months, although there are exceptions. Some cats may survive for a year or more and may have periods of time when they are not receiving chemotherapy.”
While lymphoma cannot be prevented, she notes, the chances that a cat will develop the disease may be reduced through vaccination against FeLV, by preventing contact with FIV or FeLV infected cats, and by making sure it does not live in an environment contaminated by tobacco smoke. Since early detection of the disease may improve an animal’s chances for survival, Dr. McEntee also recommends that all cats seven years of age and older undergo twice-yearly physical examinations that include blood chemistry testing and thorough palpation of the patient’s body.
By Tom Ewing
December 20, 2010