The lymphomas (malignant lymphoma or lymphosarcoma) are a diverse group of cancers that originate from a type of white blood cell called a lymphocyte. Lymphoma is one of the most common cancers diagnosed in dogs and cats. This cancer usually arises in lymph tissues such as lymph nodes, spleen, liver, and bone marrow; however, it can arise in almost any tissue in the body. In the cat, it is most commonly found in the intestinal tract.  Lymphoma generally develops in middle-aged to older dogs and cats. In most cases, the cause of lymphoma is unknown; however, a weak association with herbicides (weed killers) is known in the dog and the feline leukemia and immunodeficiency viruses can occasionally cause the disease in cats.

What Are the Signs of Lymphoma in Dogs and Cats?

Because lymphoma can affect any tissue in the body, symptoms can be vague and may reflect the organ that is involved. Signs of lymphoma can include the following: Generalized lymph node swelling; loss of appetite, weight loss, vomiting and/or diarrhea; lethargy; excessive drinking and urination; skin lesions

What Diagnostic Tests are Needed?

In most cases a needle aspirate or biopsy of the affected organ(s) is required to make the diagnosis.  In addition to establishing a diagnosis based on cytology or biopsy, several other tests are recommended prior to treatment. These tests are used to establish the stage of the disease (i.e. how advanced the cancer is) and to more accurately determine the individual prognosis. A special type of analysis of the biopsy/cytology, called immunophenotyping, is recommended in dogs to determine whether the cancerous lymphocyte is a “B-cell” or a “T-cell” type.  This is important because dogs with T-cell disease (approximately 20-25% of cases) typically do not respond as favorably to treatment when compared with dogs with B-cell disease. Additionally, blood tests to assess the overall health of the pet are important because treatment adjustments may be needed if other medical problems are present.

What Treatment is Recommended for Lymphoma?

In general, most pets with lymphoma have involvement of multiple glands and/or multiple organs.  Therefore, the best treatment modality is considered to be systemic medication (i.e. chemotherapy), as the drugs will be distributed throughout the body.  The treatment of choice for lymphoma involving multiple glands is a combination of chemotherapy drugs given into the vein in a cyclic fashion either weekly or every other week. This type of treatment will usually result in remission (absence of disease) within 2 to 4 weeks in 80-90% of dogs with B-cell lymphoma and 60-80% of dogs with T-cell lymphoma, and 50-65% of cats. Treatment is normally continued for 6 months, though this may vary depending on the protocol used. After the treatment is stopped, dogs and cats are checked monthly for recurrence of their cancer.

Alternatives to multi-drug chemotherapy protocols exist. These usually involve the use of just one or two of the drugs used in combination protocols.  In general, these protocols tend to be less effective; but they require fewer visits, are less costly, and have typically fewer side effects. Steroids, such as prednisone, can be used in an attempt to slow tumor progression or temporarily improve quality of life, though the length of benefit is typically short (1-3 months).  Your oncologist will explain the relative benefits of these treatment paths to help your family determine the most appropriate course of action for your pet. In rare cases where lymphoma only involves a single site (e.g., one skin lesion, bone, nasal cavity), surgery and/or radiation therapy may be the best treatment.  It should be remembered, however, that the disease might eventually return in a “multi­centric” form months or years later.

What is the Prognosis for Pets with Lymphoma?

The goal of chemotherapy is to induce a remission in your pet’s cancer.  Remission means “regression” of the cancer. Remission may be partial, indicating the overall cancer burden has been reduced by at least 50%, or complete, which means the cancer is no longer detectable by physical examination or standard screening tests. Without treatment, dogs and cats with lymphoma in multiple organs live an average of 6 weeks. However, this varies with the type and extent of lymphoma. The average lifespan for dogs with B-cell lymphoma treated with multi-drug chemotherapy is 1 year, with approximately 25% living 2 years or longer.  Dogs with T-cell lymphoma generally do not respond to treatment as well and their average survival time is 6-10 months.  In the cat, median survival time with treatment is 7-9 months; however, if a complete response is achieved the expected lifespan may be significantly increased. It is important to remember that these are average survival times and some pets will live much longer (including cures in 5% of cases), whereas others, unfortunately, have resistant cancers and respond for shorter periods of time or do not respond at all.