What is lymphoma?

Lymphoma (also called malignant lymphoma or lymphosarcoma) is cancer of a type of white blood cell called a lymphocyte. Lymphoma cancer cells are localized to tissues. Lymphoma differs from leukemia. Leukemia is also a white blood cell cancer, but the cancer cells are circulating in the blood stream.

Lymphoma is the most common tumor of blood forming cells seen in both dogs and cats. Typically, canine patients are middle aged to older, but any age can be affected. For cats, there are two distinct age groups. Younger cats (ages about 1 to 3 years) and middle aged to older cats. The younger group is primarily associated with feline leukemia virus infection. The middle aged to older group is not associated with feline leukemia virus infection. With the advent of good vaccines, the younger group has gotten much smaller in recent years.

Because the blood travels to every part of the body, lymphoma can be seen in all parts of the body. The most common sites include: lymph nodes, spleen, liver, eyes and intestines. There are also forms that localize to the skin.

Dogs commonly present with one to all of the peripheral lymph nodes enlarged. The dog has a decreased appetite and is lethargic. Sometimes the dog is anorexic. Usually the onset appears to be relatively fast.

It is common for cats to present with decreased appetite, vomiting, diarrhea, weight loss and lethargy. It is also not unusual for cats to be anemic. Onset is usually over a few weeks.

A diagnosis of lymphoma can usually be accomplished by fine needle aspiration and cytology. For some tissues, like the intestines, the only way to get a sample is by biopsy. Frequently, a histologic type of lymphoma can be made with cytology, this is actually very uncommon for the many types of cancer seen.

Once a diagnosis of lymphoma is made, there are 3 basic options to consider. The least aggressive is to provide supportive care and euthanize at an appropriate time to prevent suffering. The middle of the road option is to treat with prednisone. This option only provides palliative therapy. It alleviates many of the symptoms and stimulates the appetite. Many pets will do well with this for one to two months.

The most aggressive and expensive option to treat lymphoma is chemotherapy. Most veterinarians will refer patients to an oncologist for this treatment. Treatment involves a combination of several chemotherapeutic drugs, some given by intravenous injection and some by mouth, and oral prednisone. About 90% of dogs and 70% of cats (except feline leukemia infected cats) respond well and achieve remission. However, most patients will later succumb to chemotherapy resistant lymphoma. Median survival times in dogs are about 12 months, and in cats about 6 months. At 2 years after initiation of chemotherapy, approximately 25% of dogs and 35% of cats will be alive.

Chemotherapy is not without side effects. Unlike humans, dogs and cats do not lose their hair. However, immunosuppression is a common problem, as are vomiting, diarrhea, and infections. I have seen many dogs need intensive supportive care after a chemotherapy session. That being said, most dogs and cats handle chemotherapy relatively well. This is a type of cancer that the initial therapeutic response is often very rapid and quite dramatic.

The treatment options above are all reasonable. Some patients are not good candidates for prednisone or chemotherapy. Unfortunately, expense must also be considered as a major factor. Quality of life must be maintained. When the quality of life becomes poor with no hope of improvement, it is time to end the suffering and euthanize.

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