Diagnosis and Treatment of Feline Lymphoma

Lymphoma is a cancer of a specific white blood cell called the lymphocyte. Lymphocytes are the major cells found in lymph nodes. The lymph system is found in blood and tissues throughout the body; it is a network of vessels and nodes through which foreign proteins and disease organisms are circulated. Lymphocytes have several roles in the immune system, including the production of antibodies and other substances that fight infection and disease. With lymphoma the cancer cells invade and destroy normal tissues. In cats, lymphoma cells (like lymphocytes) can grow anywhere in the body, but there are certain sites that are more commonly affected by lymphoma than others (such as the GI tract, mediastinum, and lymph nodes). As the disease progresses, lymphoma can affect other organs in the body. Clinical signs of general malaise (i.e., lethargy, decreased appetite, vomiting, and diarrhea) progress and ultimately results in death.

Diagnosis

A cat with lymphoma may demonstrate only very vague problems. Progressive lack of appetite, lethargy and weight loss are among the most common. Depending on which organs are affected, other signs such as chronic diarrhea, vomiting and difficulty in breathing may occur. Many diseases can cause similar symptoms, and as with any problem, diagnosis should be based on examination by your veterinarian and appropriate tests. Diagnosis of lymphoma in cats is based on a series of observations and tests. A physical exam may reveal swellings in the lymph nodes or the gastrointestinal tract (GI tract). Diagnostic imaging may show tumors or swellings in other internal organs. Testing for Feline Leukemia Virus (FeLV) and Feline Immunodeficiency Virus (FIV) may reveal that a cat is positive for one of these diseases, which increases the likelihood that they could develop feline lymphoma. A chemistry panel and complete blood count (CBC) may reveal organ involvement. Fine needle aspirates or biopsies are often diagnostic for feline lymphoma. In some cases, surgery may be recommended for confirmation of diagnosis and as a possible initial treatment.

Forms of Feline Lymphoma

Feline lymphoma has several different forms. In all forms, the tumors consist of abnormal proliferation of lymphoid tissue. Because lymphocytes and lymph tissue are found throughout the body, lymphoma can appear almost anywhere and affect a wide number of organs. However, lymphoma most commonly appears in three parts of the body. The location is often associated with the cause of the lymphoma and will influence the symptoms, treatment, and prognosis:

The multicentric form generally involves multiple lymph nodes and possibly multiple organs. This form is more closely associated with feline leukemia and the prognosis is not as good if the cat is feline leukemia positive. The mediastinal form has historically also been associated with feline leukemia, although recently we are seeing more cats with this type of lymphoma that do not have feline leukemia. This form is found in the chest cavity and will affect the thymus and associated lymph nodes.

The alimentary form affects the digestive tract and surrounding lymph nodes. This form is least likely to be associated with feline leukemia. Alimentary (intestinal) lymphoma is the most common form of lymphoma in cats. The average patient is a senior cat (9-13 years) with a history of vomiting, diarrhea, weight loss, inappetence or any combination of the above.

In addition to different body sites that can be affected, lymphoma can be categorized by the type of cells of which it is composed. In general, there are two main types of lymphoma:

1. High Grade (or Large Cell) Lymphoma

2. Low Grade (or Small Cell) Lymphoma

These two types of lymphoma vary in behavior so a definitive diagnosis will affect the treatment recommendation.

Treatment & Prognosis

High Grade Lymphoma

Treatment for high grade feline lymphoma usually consists of chemotherapy; a combination of drugs including L-asparaginase, doxorubicin, cyclophosphamide, vincristine, and prednisone are administered over several weeks. During treatment white and red blood cell numbers are closely monitored. In a few isolated cases (where the tumor is localized and easily accessible) surgery or radiation therapy may be used. An actual mass may develop with intestinal lymphoma, or a tumor may be more infiltrative. An actual mass can potentially cause obstruction in the intestine and lead to a crisis that must be promptly resolved with surgery.

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. Tests on animals with lymphoma that are in complete remission can have normal results. A cat in remission will not have any signs of cancer, and all masses or lumps will have disappeared. They eat, drink, and run just as they did before they developed cancer. Complete remission is achieved in 50-75% of cats, but cats that achieve only partial remission also feel better according to owners. The average survival for cats is 6 – 9 months, but the length of remission depends on several factors. These include

1. The primary site of the cancer

2. How sick an animal is at the start of treatment

3. The feline leukemia status: Cats that test positive for FeLV or FIV have a lower rate of response to therapy, as well as a shorter average survival time when treated.

4. How quickly the tumor is diagnosed (and treated)

5. The extent of disease

Some of the cancer cells do survive in an animal in complete remission, but the numbers of these cells 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”. When lymphoma returns, remission may be re-established in most cats by changing the chemotherapy protocol to a new set of chemotherapy drugs. Eventually, the cancer cells will become resistant or insensitive to all drugs and the cancer will no longer respond to therapy. A small percentage of cats that respond will go into a more complete remission that can last for 2 years or longer. This potential response is encouraging and is the reason that treatment for lymphoma in cats is so highly recommended. Cats with lymphoma who are not treated with chemotherapy have an average survival time of 4 weeks once the diagnosis has been made.

Cats with intestinal lymphoma who are treated with prednisone alone have a life expectancy of 60-90 days. Other protocols using multiple drugs yield significantly better results.

Keep in mind that these numbers represent average values. Each cat is an individual and will respond to treatment differently. The term “cure” refers to the permanent removal of all traces of tumor such that no further treatment is needed. In effect, it is a permanent state of remission. While this is a possibility, it is more constructive and realistic to focus on increasing quality of life. In general, approximately 50-70% of cats will respond to chemotherapy treatment.

It is important to understand that despite how localized a tumor appears to be, simply removing the mass will not be curative. Surgical removal does not significantly add to the survival time achieved by chemotherapy. It is rare to cure lymphoma. Chemotherapy increases the chances of long-term survival and, in most, will extend the quantity and quality of life.

Low Grade Lymphoma

Low grade (small cell) lymphoma occurs most commonly in the gastrointestinal (GI) tract of cats. The behavior of low-grade lymphoma is different than large cell lymphoma in that it has a more indolent course; it grows more slowly. Given this, different chemotherapy drugs are used in its treatment. Typically, oral chemotherapy drugs (chlorambucil and prednisolone) are used. Most cats (85-90%) will respond to treatment, however it may be a few weeks before we start to see a response in some cats. Survival times with treatment for cats with low grade lymphoma average about 1.5-2 years.

SIDE EFFECTS OF TREATMENT (BOTH FORMS OF LYMPHOMA)

The exact drugs and schedule will depend upon how aggressively the cancer is behaving, how sick an animal is at the start of treatment, and any abnormalities in organ function (changes in liver and kidney function are especially important). Some of the drugs are given as an injection and some are given orally (this can generally be done at home). Toxicities can occur (10% risk) with chemotherapy but are generally mild. Most cats will tolerate chemotherapy well and have minimal side effects. Veterinary chemotherapy is designed to extend a pet’s life if possible while maintaining a good quality of life. As a result, the undesirable side effects normally associated with human chemotherapy are both less common and less severe in animals.

Side effects such as nausea and anorexia are occasionally noted, however the most common side effect is bone marrow suppression. In 1-2% of patients this can lead to life-threatening infections that require hospitalization. While whiskers are commonly lost, animals on chemotherapy do not experience substantial hair loss. Unfortunately, the only way to know whether an animal is going to have a drug reaction is to administer the drug. Some cats never get sick during chemotherapy, while others are very sensitive to the drugs. If your cat has a serious reaction, the drugs, or doses he or she receives may be individually adjusted to maintain a good quality of life.

As an owner, you can help your cat with lymphoma by watching him or her closely after each treatment. Chemotherapy may suppress your cat’s white blood cell production and make him or her more susceptible to infections. These infections generally arise from bacteria that normally live in the intestinal tract, respiratory tract, urinary tract, and on the skin (not from the environment). Signs of an infection may include loss of appetite, vomiting, diarrhea, decreased activity, or depression. Call your veterinarian immediately if your cat appears ill while receiving chemotherapy. These signs are usually only brief reactions to the drugs, but prompt treatment can often prevent more serious side effects from developing.

Your choice

The most essential aspect of cancer therapy is that you feel as comfortable as possible with your decision. There are no right or wrong answers, and each situation is different. What is right for one cat and their owner may be unacceptable to another family. If chemotherapy is not an option, either financially, logistically, or philosophically, you may consider treatment with prednisone. This can significantly improve quality of life, is inexpensive, has few significant side effects, and is an oral medication. Weekly rechecks are not necessary but monthly visits to your regular veterinarian are recommended.

If you have any questions or need help making the best decision for you and your cat, please let me know.

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Modified from Ethos Veterinary Health