Lymphoma in Pets

 Lymphoma is a cancer of a specific white blood cell called the lymphocyte. Lymphocytes are found throughout the body in blood and tissues and act to protect the body from infec-tion. Lymphocytes are the major cells found in lymph nodes or "glands." In lymphoma, the cancer cells invade and destroy normal tissues. The most common site for lymphoma is the lymph nodes, but lymphoma cells, like lymphocytes, can grow anywhere in the body. In most dogs and cats with lymphoma, the cancer cells are present in multiple lymph nodes and tissues.

Chemotherapy is the treatment of choice for almost every dog and cat with lymphoma. Chemotherapy is the administration of drugs by injection or by mouth to kill cancer cells. The chemotherapeutic drug circulates throughout the body. This is important for lymphoma because the cancer cells are in many places at once. Surgery and radiation therapy are less useful in lymphoma because these treatment methods attack cancer cells at only one site.

The goal of chemotherapy for animals with lymphoma is to induce a complete "remission" by killing most of the cancer cells. "Remission" means that all symptoms of the cancer have temporarily disappeared. Animals with Iymphoma that are in complete remission look like normal animals by all tests. They do not have any signs of cancer, and all masses or lumps have disappeared. They eat, drink, and run just as they did before they developed cancer. Some of the cancer cells do survive in an animal in complete remission, but the numbers are too small to detect. Eventually, these few cells will grow and the cancer will become evident again. When this happens the animal is said to be "out of remission." Sometimes a second remission can be achieved with additional chemotherapy. Eventually, the cancer cells will become resistant or insensitive to all drugs and cause the dog or cat to die.

Veterinarians use many different drugs and drug combinations called "protocols" to treat lymphoma in dogs and cats. No one knows the "best" treatment, and many protocols give similar results. In general, the longest survival times are reported for protocols that use a combination of drugs and include more expensive drugs.

Although chemotherapy does not cure dogs and cats with Iymphoma, in most it does extend the quantity and quality of life. About 80 to 90 per cent of dogs with lymphoma attain a complete remission with an average survival of 1 year, and 25 per cent of dogs live 2 years. For cats, the remission rate is lower, with about 50 per cent attaining a complete remission, but cats who achieve only partial remission also feel better according to owners. The average survival for cats is 7 to 10 months.

Veterinarians use chemotherapy to give dogs and cats with lymphoma a good quality of life with minimal side effects. Most dogs and cats with lymphoma feel good even though they are receiving chemotherapy. The potential for side effects does exist, however, and varies with the protocol used. The most common side effects include decreased energy, decreased appetite, vomiting, and diarrhea.

Occasionally, more severe side effects occur, and in rare cases an animal receiving chemotherapy will die as a result of treatment. Unfortunately, the only way to know whether an animal is going to have a drug reaction is to give the drug. Some animals never get sick during chemotherapy, but others are very sensitive to the drugs. If your pet has a serious reaction, the drugs or doses your pet receives may be individually adjusted to maintain a good quality of life.

As an owner, you can help your pet with lymphoma by watching the pet closely after each treatment. Chemotherapy will suppress your pet's immune system and make him or her more susceptible to infections. These infections generally arise from bacteria that normally live in the intestinal tract and on the skin, not from the environment. Signs of an infection may include loss of appetite, vomiting, diarrhea, decreased activity, or depression. Phone your veterinarian immediately if your pet appears ill while receiving chemo-therapy. These signs are usually only brief reactions to the drugs, but prompt treatment can often prevent more serious side effects from developing.

The above is general veterinary information. Do not begin any course of treatment without consulting your regular veterinarian. All animals should be examined at least once every 12 months.

About the author:

From the Textbook of Veterinary Internal Information: Client Information Series. Copyright © 2000 by W.B. Saunders Company. All rights reserved.

Linda Mar Veterinary Hospital and its cat-only affiliate, Coastal Cat Clinic, are small animal practices located in Pacifica, California. To find a veterinarian or to learn more about the vet clinic and our staff, visit:[http://lindamarvet.com/]

 Susan A. Kraegel, DVM