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 is found throughout many areas of the body which include: lymph nodes, spleen, liver, gastrointestinal tract and bone marrow.
Unlike lymphoma in dogs, viral causes of feline lymphoma are well defined, and the feline leukemia virus (FeLV) has been shown to cause a significant (~60 fold) increase in risk for development of lymphoma in cats. We typically see lymphoma diagnosed 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 which is dependent on location of the tumor. These locations can include:
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 are usually young and often seen because of a sudden onsent of difficulty breathing, decreased energy level and decrease in appetite.
Renal: The kidneys can 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. Most patients are presented to the hospital for a decrease in energy and appetite. Bloodwork, usually reveals a change in their red blood cell and white blood cell counts.
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 site of involvement
Diagnosis and Initial Evaluation
A biopsy (tissue) or cytology (aspirate) 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 in other situations, 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.
The first step for any patient suspected of having lymphoma includes determining the extent of the disease which is known as staging. This includes 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 include chest radiographs, abdominal ultrasound along with possible bone marrow aspirate and CT/MRI. Once we determine the extent of disease, we can then decide on the best treatment for your pet.
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. Specific recommendations will be discussed based on your pet’s particular situation.
Fortunately, lymphoma is very responsive to chemotherapy where 50-70% 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 your pet is at the time of diagnosis and the extent of disease. In most situations, the median remission and survival times (with chemotherapy) are between six to twelve months; with 25% of cats experiencing disease control for greater than one year and approximately 10-15% of cats living longer than two 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 and/or 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 progresses down the road, then chemotherapy can be considered at that time.
The exact chemotherapeutic drugs and schedule will depend upon how aggressively the cancer is behaving, how sick your pet is at the start of treatment, any abnormalities in organ function (particularly kidneys and liver), and the goals of treatment. Chemotherapy is most effective when we used a combination protocol; therefore, most protocols generally consist of 4-6 different drugs. This is called a multi-drug protocol. Multi-drug protocols most commonly include Elpsar (L’asparaginase), Vincristine (Oncovin), Cytoxan (Cyclophsophamide), Adriamycin (Doxorubicin) and Prednisone. 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. Bloodwork and/or X-rays/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 your pet’s response to treatment.
Fortunately, most cats tolerate chemotherapy very well and experience minimal side effects. Serious side effects are only seen in 5% of the patients which require outpatient care and less than 1% will require hospitalization or experience any life threatening side effects. 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, so close monitoring with bloodwork is recommended. Cats do not lose their hair but may lose their whiskers and have a different texture to their fur secondary to chemotherapy.
The ultimate goal of any treatment is to improve your pet’s quality of life and your oncologist will work with you to determine the treatment option that you feel most comfortable with.