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 a number of 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. Signs of general malaise (i.e., lethargy, decreased appetite, vomiting, and diarrhea) progress and ultimately results in death or euthanasia of a pet.

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. 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 overgrowth 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 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:

• high grade (or large cell) lymphoma

• low grade (or small cell) lymphoma

These two types of lymphoma vary in behavior and prognosis, 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, cyclophosphamide, vincristine, prednisone, +/- doxorubicin are administered over several weeks. During the course of 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. Lymphoma localized to one area, such as nasal lymphoma, is best treated with radiation therapy; however, we do not have radiation oncology in the state of Hawaii, and this would require referral to a facility on the mainland.

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 as well as any associated masses or enlarged lymph nodes 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.

The prognosis for cats with large cell, or high grade, lymphoma depends on their response to treatment. Approximately one-third of cats will go into a complete remission during treatment and experience better outcomes with median survival times of approximately 6 to 9 months from the time of diagnosis. Approximately one-third of cats will go into a partial remission, meaning they respond to chemotherapy with improvement in their clinical signs and reduction in the size of their masses/lymph nodes; however, these cats will progress while still undergoing treatment, and their outcomes will be shorter. The remaining one-third of cats will not respond to treatment and experience the poorest outcomes. There is no way to determine which group a cat will fall in until we try a treatment.

There are some other factors that can influence outcomes, including:

• The primary site of the cancer

• 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.

• How quickly the tumor is diagnosed (and treated)

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 restarting chemotherapy either with the same protocol they previously responded to or with a new protocol. 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 highly recommended.

• Cats with large cell lymphoma who are not treated with chemotherapy have an average survival time of weeks to months once the diagnosis has been made.

• 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 cancer such that no further treatment is needed. In effect, it is a permanent state of remission. Unfortunately, we do not cure cats of lymphoma in the vast majority of cases. 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. Chemotherapy increases the chances of long-term survival and, in most cases, 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.

Toxicities can occur 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 as long as 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. 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. In general, for veterinary patients receiving chemotherapy, <10% may require hospitalization for chemotherapy-associated side effects, and <1% may die or be euthanized due to side effects.

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.

Am I Making the Right Decision?

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, please strongly 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 us know.