Lymphosarcoma, commonly called lymphoma, is one of the most common cancers diagnosed in cats. It is a cancer of the lymphocytes (a type of white blood cell) and lymphoid tissues. Lymphoid tissue is normally present in many places in the body including lymph nodes, spleen, liver, gastrointestinal tract, and bone marrow.
Unlike lymphoma in dogs, viral causes of feline lymphoma are well defined. Infection with the feline leukemia virus (FeLV) has been shown to cause a significant (~60 fold) increase in risk for development of lymphoma in cats. Cats with the feline immunodeficiency virus (FIV) are also at increased risk of developing lymphoma (7 fold) and infection with both viruses confers a 77 fold increase in risk. Cats of any age, breed, and of either sex can be affected. We typically see lymphoma in younger cats that are infected with the feline leukemia virus, and in older cats that are not infected with the virus. Other possible risk factors include exposure to second hand tobacco smoke, chronic immunosuppressive therapy, as well as chronic inflammatory diseases.
TYPES OF LYMPHOMA
Lymphoma can be subdivided into several different forms, depending on the primary or predominant site of the tumor. Some cats have multiple sites of involvement and do not fit well into just one category. These are usually animals with very advanced disease.
- Gastrointestinal Tract: The most common form is involvement of the gastrointestinal (GI) tract. This includes the stomach, intestines, and liver; as well as some of the lymph nodes surrounding the intestines. Cats with this type of lymphoma often have clinical signs consisting of vomiting, diarrhea, weight loss, or a decreased appetite.
- Mediastinal: The mediastinum is a term used for a special aggregation of lymphoid tissue in the chest. Cats with this type of lymphoma often are seen because of difficulty breathing due to a large mass in the chest or an accumulation of fluid around the lungs.
- Renal: The kidneys may be the primary sites of involvement. Cats that have this type are often seen because of signs related to kidney failure (increased thirst, increased urination, loss of appetite, vomiting).
- Bone Marrow: If the cancer were confined to the bone marrow, it is considered leukemia. The signs that we see in cats are usually related to the decreased numbers of normal cells such as red blood cells that carry oxygen, white blood cells that fight infection, and platelets that help with clotting – all of which are made in the bone marrow. Anemia (low red blood cell counts), infections, and bleeding are common problems.
- External Lymph Nodes: In a few cats, the only site of involvement is the external lymph nodes. These cats may be seen because of problems such as vomiting and loss of appetite or because the owner found “lumps” (enlarged lymph nodes) on their cat.
- Other Sites: We will occasionally see other sites such as the skin, nose, brain, and spinal cord as the primary sites of involvement
DIAGNOSIS AND INITIAL EVALUATION
A biopsy (tissue) or cytology sample is required in order to make a diagnosis of lymphoma. In some cases, we can obtain a diagnosis by a fine needle aspirate but sometimes a biopsy to obtain a larger piece of tissue is necessary to confirm the diagnosis. The ease with which a diagnosis can be obtained depends upon where the tumor is located.
A complete evaluation of a cat suspected of having lymphoma includes determining the extent of the cancer (i.e. looking for spread of the cancer to other sites) which is known as staging. A complete blood count (CBC), serum chemistry profile (which looks at things such as liver and kidney function, protein levels, blood sugar, and electrolytes), urinalysis, and FeLV/FIV testing are always recommended and provide important information regarding the effects of the cancer on body functions as well as the ability of the patient to handle chemotherapy or other treatments. Additional tests may include radiographs, abdominal ultrasound, bone marrow aspirate, and CT/MRI. Chest radiographs (x-rays) allow us to look for internal lymph nodes, lung involvement, an enlarged mediastinum or fluid around the lungs. An abdominal ultrasound allows us to evaluate the liver, spleen, internal lymph nodes, and intestinal tract for possible tumor involvement. A bone marrow aspirate allows us to look for tumor cells in the bone marrow as well as to evaluate the marrow’s ability to produce normal blood cells. Once we know the extent of disease, we can then decide on the best treatment for each individual patient.
TREATMENT AND PROGNOSIS
Chemotherapy is the mainstay of treatment for lymphoma; however, there may be situations when surgery and/or radiation are also indicated. Radiation therapy may be recommended if the cancer is localized to one site such as the nasal cavity. Often surgery or radiation therapy is used in addition to chemotherapy. Specific recommendations will be discussed based on your pet’s particular situation.
Lymphoma is very responsive to chemotherapy and 50-60% of treated cats will go into remission. The definition of remission is the complete disappearance of detectable cancer; however, microscopic amounts of tumor cells can remain hidden in the body. A remission is NOT a cure but it does allow your pet to experience a good quality of life without clinical signs associated with their disease. The length of the remission depends upon many factors including the primary site, how sick an animal is at the start of treatment and the extent of disease. In most situations, the average remission and survival times (with chemotherapy) are between six to twelve months; with about 30% of cats experiencing disease control for greater than one year and approximately 10-15% of cats living longer than 2 years.
Solitary lymphoma such as nasal is generally treated with radiation +/-chemotherapy. The radiation can be considered definitive with the intent for long-term control or palliative for symptom relief in order to improve/maintain the patient’s quality with minimal negative impact. The prognosis for solitary lymphoma such as nasal lymphoma is generally better with many cats achieving local control for 1-1.5 years although there is still a concern that the cancer may spread within 3-6 months. If solitary lymphoma is treated with radiation and the cancer spreads later in life chemotherapy can be considered at that time.
The exact chemotherapeutic 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, particularly kidneys and liver as well as the goals of treatment. Chemotherapy is more effective when we use a combination of drugs; therefore, most protocols generally consist of 4-6 different drugs. This is called a multi-drug protocol. Initially, treatments are given more frequently (i.e. once weekly) and then, depending upon the response and protocol used, are gradually spread out and/or discontinued. Other options for therapy may consist of using a single chemotherapy drug (single-agent therapy) at 3- week intervals, or palliative care which is simply designed to keep your pet comfortable at home for as long as possible. While palliative care with drugs may provide comfort it generally only yields 1-2 month survival times. A disadvantage to single-agent therapy is that remission rates and expected survival times are much more difficult to predict with these protocols. Bloodwork and/or radiographs and ultrasounds are generally repeated at regular specified intervals to monitor for side effects (such as a low white blood cell count) and to determine the pet’s response to treatment.
If a patient comes out of remission or relapses, we can try to put them back into remission using either new combinations of the same drugs or different drugs. Unfortunately, the chances of obtaining a second remission are lower; however, there are some cats that do respond and have additional time with a good quality of life.
Most cats tolerate chemotherapy very well and experience minimal side effects. Serious side effects are only seen in 5-10% of the patients we treat. If side effects are serious or intolerable, we can consider either lowering the dose of the offending drug or substituting a different drug. Side effects include nausea, vomiting and loss of appetite, diarrhea, extreme tiredness or rarely infection. Certain chemotherapy agents can affect organ function over time. Cats do not lose their hair but may lose their whiskers and have a different texture to their fur secondary to chemotherapy.