Lymphoma in Cats

What is lymphoma?

Lymphoma is a cancer of the lymphocytes. Lymphocytes are cells involved in the immune system and travel throughout the body in the blood and lymphatic vessels, so lymphoma may affect one area or several parts of the body.

Is lymphoma common in cats?

Lymphoma is one of the most commonly diagnosed cancers in cats, although it is less common than it once was. Infection with feline leukemia virus (FeLV) increases a cat’s risk of developing certain forms of lymphoma. FeLV testing and vaccination have helped lower the rates of FeLV infection and FeLV-associated lymphoma.

What are the common types of lymphoma?

Common forms of lymphoma in cats include:

• Gastrointestinal lymphoma affects the gastrointestinal tract. This is the most common type of lymphoma in cats, accounting for 50% to 70% of feline lymphoma cases. It is most common in senior cats, and is most often diagnosed in cats 9 to 13 years of age.
• Mediastinal lymphoma affects the lymphoid organs in the chest, including the lymph nodes and thymus. It often affects younger cats, typically around five years of age, and is often associated with FeLV infection.
• Renal lymphoma affects the kidneys and can lead to signs of kidney failure as functional kidney cells are replaced by cancer cells. Renal lymphoma may also be associated with feline leukemia, but not to the same extent as mediastinal lymphoma.

What are the clinical signs of lymphoma?

Gastrointestinal lymphoma affects the intestines, so signs are often similar to other intestinal diseases. Signs may include:

• Weight loss
• Vomiting, diarrhea
• Appetite changes (increase or decrease)

Mediastinal lymphoma occurs in the chest and is often associated with difficulty breathing. Fluid often accumulates around the tumor, making it more difficult for an affected cat to expand their lungs fully.

Renal lymphoma may be associated with signs of kidney failure, including:

• Decreased appetite
• Weight loss
• Increased thirst
• Vomiting

How is lymphoma diagnosed?

Physical examination. Your veterinarian may detect enlarged lymph nodes or other abnormalities during a physical examination. Because infections and immune-mediated diseases can also enlarge lymph nodes, further testing is needed to determine the cause.

Blood tests. Your veterinarian will likely perform blood tests to assess your cat’s overall health. These tests usually include a complete blood count (CBC), which measures red blood cells, white blood cells, and platelets, and a serum biochemistry panel, which helps assess organ function.

Fine-needle aspiration. In some cases, lymphoma can be diagnosed with fine-needle aspiration (FNA). During this test, your veterinarian inserts a needle into an enlarged lymph node or another affected organ and collects a small sample of cells. These cells are examined under a microscope to look for lymphoma.

Biopsy. If the FNA results are inconclusive or the affected area is difficult to sample, your veterinarian may recommend a biopsy. A biopsy involves removing a small tissue sample from the affected area. For suspected gastrointestinal lymphoma, biopsy samples may be collected using endoscopy or may require abdominal surgery. The sample is sent to a veterinary laboratory to be examined under a microscope.

A biopsy can also help determine whether the lymphoma is low-, intermediate-, or high-grade, based on how quickly the cancer cells appear to be dividing and how malignant the cells appear. Low-grade lymphoma usually grows more slowly and often responds well to chemotherapy. High-grade lymphoma grows more quickly and is more aggressive.

If lymphoma is diagnosed, additional tests may be recommended to learn more about the lymphoma and develop a treatment plan. These tests may include:

• Immunohistochemistry. This test uses specialized stains on a tissue sample to distinguish between two types of lymphoma (B-cell lymphoma and T-cell lymphoma). Identifying the type can provide information about the prognosis.
• Flow cytometry. This test analyzes cells from an aspirate or blood sample and can also help distinguish B-cell lymphoma from T-cell lymphoma.

Your veterinarian may also recommend additional tests, called staging tests, to determine how far the lymphoma has spread. A staging system is used to describe the spread of the lymphoma in the body and can help guide treatment decisions.

How is lymphoma treated?

Lymphoma is treated with chemotherapy. Low-grade lymphoma is treated with prednisolone (a steroid) and chlorambucil (an oral chemotherapy agent). High-grade lymphoma is treated using one of several injectable chemotherapy protocols.  Most cats tolerate chemotherapy well; they rarely lose their hair or appear sick. The most common side effects of chemotherapy include vomiting, diarrhea, and decreased appetite, although these effects are seen in only about 10% of patients.

Surgery or radiation may be appropriate for lymphoma confined to one area, but most cases cannot be successfully treated with surgery or radiation.

If chemotherapy is not an option because of the pet’s overall health, cost, or practical considerations, prednisolone can be used for palliative care. Although prednisolone does not treat lymphoma, it can provide temporary relief and improve quality of life. 

What is the prognosis for lymphoma?

The prognosis for lymphoma depends on its location and grade, the cat’s overall health, their FeLV status, and how quickly the disease is diagnosed and treated. When lymphoma responds to treatment, a cat may go into remission. Remission means that the signs of lymphoma temporarily disappear; it does not mean that the cancer has been cured.

• Low-grade gastrointestinal lymphoma responds well to treatment. Approximately 70% to 90% of affected cats go into remission. Remission commonly lasts 1.5 to 3 years.
• High-grade gastrointestinal lymphoma does not respond as well to treatment. Approximately 25% to 50% of affected cats go into remission, which commonly lasts only 4 to 12 months.
• Mediastinal lymphoma has a poorer prognosis in cats that test positive for FeLV, with a typical survival time of approximately 3 months. Cats without FeLV often respond better to chemotherapy and may survive for 9 to 12 months. Cats that respond well to initial treatment may have longer survival times.
• Renal lymphoma also has a poor prognosis, with a typical survival time of 3 to 6 months, although there are isolated reports of cats surviving far longer. This form of lymphoma may spread to the brain or other parts of the central nervous system, which can worsen the prognosis.

How can I reduce the likelihood of my cat developing lymphoma?

Lymphoma cannot always be prevented. However, preventing infection with feline leukemia virus (FeLV) can reduce the risk of FeLV-associated lymphoma. FeLV vaccination is recommended for all kittens and adult cats at continued risk of exposure, such as cats that go outdoors or have contact with cats whose FeLV status is positive or unknown. Your veterinarian can recommend an appropriate testing and vaccination plan based on your cat’s risk.

FeLV vaccination does not prevent every form of lymphoma. Regular veterinary examinations can help detect changes in your cat’s health as early as possible.