Lymphoma in Dogs

Lymphoma is one of the most common types of cancer in dogs. Different forms of this cancer occur in specific parts of the body, but all affect white blood cells. The most obvious symptom is swelling of lymph nodes in one or more areas of a dog's body. Learning more about lymphoma can help pet caregivers be able to quickly recognize symptoms and act efficiently in getting their dogs the help they need.

What Is Lymphoma?

Canine lymphoma is a broad term that describes any type of cancer that involves lymphocytes, a type of white blood cell. However, there are many different forms of canine lymphoma, which are generally classified by the area of the body primarily affected and the type of lymphocyte involved. 

Lymphocytes are an important part of the immune system. Lymphocytes can be found anywhere in the body, but a large number of these cells are found in the lymph nodes, spleen, and intestinal tract. Because lymphocytes are found throughout the body, lymphoma can develop almost anywhere. 

Symptoms of Lymphoma in Dogs

The most common initial symptom of lymphoma is the presence of one or more enlarged, firm, and non-painful lymph nodes. Many dogs with lymphoma appear to feel just fine, but others can develop nonspecific signs like lethargy and loss of appetite.

Lymph nodes exist at many points throughout your dog’s body. Although there are dozens of lymph nodes throughout the body, only a few are easily palpable during a physical examination. The peripheral lymph nodes veterinarians and pet caregivers may be able to feel include:

• Submandibular: located beneath the back of the jaw
• Prescapular: located in front of the shoulder region
• Axillary: located in the armpits
• Inguinal: located in the groin
• Popliteal: located behind the knees

Other symptoms typically relate to the location of the cancer. For example, with alimentary (abdominal) lymphoma, your dog may experience loss of appetite, nausea, vomiting, and diarrhea; lymphomas within the chest cavity can lead to difficulty breathing.

Causes of Lymphoma

According to the Purdue University College of Veterinary Medicine, “Unfortunately, the cause of lymphoma in dogs is not known."

Possible causes include:

• Viruses
• Bacteria
• Chemical exposure
• Physical factors such as strong magnetic fields
• Genetics

Diagnosing Lymphoma in Dogs

To diagnose lymphoma, the initial step is often a complete physical exam and a fine needle biopsy of the enlarged lymph node(s) submitted to a veterinary laboratory for analysis.

In addition, a complete blood count, chemistry profile, and urinalysis should be performed to identify abnormalities. Radiography of the chest and abdomen, plus abdominal ultrasound and/or a bone marrow biopsy may also be recommended to help determine the stage of the disease. Lymphoma stages are based on what organs are affected and how many are involved, as well as sub-stages based on how the pet feels and how they are affected systemically.

The purpose of the staging tests is to determine how far the lymphoma has spread throughout a dog’s body. Staging tests also help your veterinarian assess whether your dog has any other conditions that may affect treatment decisions or overall prognosis.

The stages are:

• Stage I: Single lymph node involved
• Stage II: Multiple lymph nodes in the same region involved
• Stage III: Multiple lymph nodes in multiple regions involved
• Stage IV: Liver and/or spleen involved (may or may not have lymph node involvement)
• Stage V: Bone marrow or blood involvement and/or another organ besides the liver, spleen, and lymph nodes involved  

Treatment

There is currently no known cure for canine lymphoma, but it is one of the most treatable types of cancer in dogs.

The most effective therapy for most types of canine lymphoma is chemotherapy. There is a wide variety of chemotherapy protocols and drugs that are currently being used to treat lymphoma. The treatment usually consists of a combination of oral and injectable drugs given every week. Some commonly used drugs include cyclophosphamide, vincristine, doxorubicin, and prednisone. The exact treatment protocol will vary depending on the veterinarian and the specifics of the case. 

Fortunately, most dogs only experience mild side effects from chemotherapy and enjoy an excellent quality of life during treatment. Since lymphoma is generally not a curable disease, the goal of lymphoma treatment is to induce a lengthy remission, during which time all symptoms of cancer have temporarily disappeared.

Prognosis for Dogs with Lymphoma

The prognosis depends on multiple factors including how the dog feels, what stage the cancer is, what stage it was when diagnosed, and treatments used.

In general, the more places the lymphoma has spread, the poorer the dog’s prognosis. However, dogs with very advanced lymphoma can still be treated and experience cancer remission or a meaningful improvement in their quality of life.

The prognosis with chemotherapy is relatively good, with most dogs experiencing either a partial or complete remission and a life expectancy of around one year, on average.

How to Prevent Lymphoma in Dogs

Lymphoma is not preventable, but keeping your dog healthy throughout its life is a great way to prevent or delay many cancers and other diseases.