Lymphoma in Dogs

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 dogs?

Lymphoma is a relatively common cancer in dogs, accounting for 15% to 25% of new cancer diagnoses. It is most common in middle-aged and older dogs, and several breeds are predisposed, suggesting that there may be a genetic component to lymphoma, although this has not been confirmed. Some breeds predisposed to lymphoma include:

• Basset Hound
• Beagle
• Boxer
• Bullmastiff
• English Bulldog
• German Shepherd
• Golden Retriever
• Poodle
• Rottweiler
• Saint Bernard
• Terriers (Scottish, Airedale, West Highland White, Yorkshire, and Bull Terriers

What are the common types of lymphoma?

There are four types of lymphoma in dogs, classified by the areas of the body they affect:

• Multicentric (systemic) lymphoma. This is the most common type of canine lymphoma. Multicentric lymphoma accounts for approximately 80% to 85% of cases in dogs. In multicentric lymphoma, lymph nodes throughout the body are affected.
• Alimentarylymphoma. This type of lymphoma affects the gastrointestinal tract. Alimentary lymphoma is the second-most common type of lymphoma. 
• Mediastinal lymphoma. In this rare form of lymphoma, lymphoid organs in the chest are affected (e.g., lymph nodes, thymus).
• Extranodal lymphoma. This type of lymphoma targets a specific organ outside of the lymphatic system. Extranodal lymphoma is rare but may develop in the skin, eyes, kidney, lung, or nervous system.

What are the clinical signs of lymphoma?

The signs of lymphoma depend on the type

• Multicentric (systemic) lymphoma causes swelling of the lymph nodes. The lymph nodes in the neck, chest, armpits, groin, and behind the knees are often the most easily observed. Many affected dogs feel well when they are diagnosed, although they will often develop signs if untreated, such as weight loss and lethargy.
• Alimentary lymphoma affects the intestines, so clinical signs are often similar to other intestinal diseases. Signs may include vomiting, diarrhea, and weight loss.
• Mediastinal lymphoma creates lesions that take up space in the chest cavity, commonly resulting in coughing and shortness of breath. 
• Extranodal lymphoma has variable signs that depend on the organ involved.

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 dog’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. The most common test to diagnose lymphoma is 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. The sample is sent to a veterinary laboratory to be examined under a microscope.

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. These tests may include radiographs (X-rays) or ultrasounds. 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. There are several chemotherapy protocols, but most consist of a combination of injections given every week. Most dogs 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 not seen in all dogs.

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, prednisone can be used for palliative care. Although prednisone 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  the type of lymphoma your dog has. On average, dogs that receive no treatment or are treated with prednisone alone have an expected survival of four to six weeks. However, this is an average, so some dogs may die before the four-week point and some may live past six weeks.

With chemotherapy, lymphoma can often be put into remission. Remission means that the signs of lymphoma disappear; it does not mean that the cancer has been cured. The average remission with chemotherapy is eight to nine months, with an average survival time of approximately one year. Your veterinarian may be able to provide more specific information on your pet’s prognosis if you pursue additional testing to characterize the lymphoma better.