What is canine lymphoma?

• Canine lymphoma (also called lymphosarcoma) is a common cancer in dogs.
• Lymphoma is a cancer of lymphocytes, which are white blood cells that play a role in the body’s immune response in the fight against germs and diseases. 
  
• Symptoms vary according to the part of the body affected, but the most common symptom is enlarged lymph nodes.
  
• Diagnosis requires collecting a sample from the affected tissue, which can often be obtained with a needle sample and with the patient awake.
  
• Investigating the disease further with diagnostic tests (called “staging”) helps determine the best treatment course.
  
• While canine lymphoma is often aggressive when left untreated, it often responds quite well when treatment is pursued, adding months to years to the patient’s life.
  

How common is canine lymphoma?

Canine lymphoma (also called lymphosarcoma or LSA) is one of the most common cancers of dogs, accounting for approximately 7% to 24% of all canine cancers. Lymphoma is a cancer of white blood cells (the immune system) called lymphocytes that can affect any part of the body. While it typically affects middle-aged and older dogs, it can occur in any aged dog, as well as any breed. 

What causes canine lymphoma?

Though we do not know what causes lymphoma, it occurs when there is a change within the lymphocyte cell that causes it to become destructive and capable of reproducing without limits, and even invading other tissues. Some factors that may contribute to the development of lymphoma include:

• Genetic predisposition
• Viral infection
  
• Exposure to herbicides or electromagnetic radiation
  

However, clear causes of lymphoma have not been determined.

What types of lymphoma can dogs get?

While lymphocytes are a specific type of cell within the blood, lymphoma is not restricted to the blood and is often thought of as a systemic disease. It may originate in the lymph nodes, spleen, liver, bone marrow, thymus, gastrointestinal tract, skin, liver, lungs, and virtually any place in the body. Learning what body parts are affected is the first step in classifying lymphoma. The most common scenario in dogs with lymphoma is a multicentric presentation; meaning that the cancer cells are affecting multiple locations. When the bone marrow or peripheral blood is affected, it is called leukemia. Microscopic examination by a veterinary pathologist can further classify lymphoma as low, intermediate, or high grade.

Furthermore, there are two main types of lymphocytes found in the body: B-cells and T-cells. The classification of lymphoma as B-cell or T-cell is important because this distinction is valuable for the specialist to predict duration of remission and overall survival. Generally speaking, B-cell lymphoma carries a better prognosis than T-cell lymphoma. Luckily, B-cell lymphoma is the more commonly diagnosed type.

While it can be quite alarming to learn your dog has been diagnosed with lymphoma, it often responds quite well to treatment. Learning as much information as possible about your dog’s specific type of lymphoma is crucial before treatment can be initiated.

What are the signs and symptoms of canine lymphoma?

Clinical features of canine lymphoma vary based on the area of the body involved. 

• Seemingly painless, generalized swollen glands (which are actually lymph nodes) that can be seen or felt under the neck, near the shoulders, or behind the knees is a common finding by pet parent or veterinarian. 
• Decreased appetite, lethargy, and weight loss are often noted, but other signs are very organ specific. 
  
• Skin lymphoma will cause generalized skin lesions that may appear as a rash initially and later progress to bigger scaly, crusted, inflamed, and hairless lesions. 
  
• Vomiting and diarrhea are seen when the gastrointestinal tract is affected. 
  
• When the cancer is found in the lungs, owners may notice shortness of breath.
  
• Elevated calcium may be found on routine blood work and pet parents may report increased thirst in such cases. 
  

It is important to remember any part of the body may be affected so the range of clinical signs seen is extensive.

How is canine lymphoma diagnosed?

Diagnosis of lymphoma can often be easily established by needle aspiration cytology or by biopsy of the tissue involved. After a diagnosis is established, staging tests are pursued to determine the extent of cancer involvement. The clinical staging evaluation can include blood work, urine analysis, chest radiographs (X-rays), and abdominal imaging (X-rays or ultrasound). Molecular staging such as flow cytometry or PARR testing can also be performed to determine the type of lymphoma (B-cell or T-cell).

While this process may sound overwhelming, moving from a diagnosis to treatment in the canine world is very swift and efficient in comparison to human health care and oncology. We encourage pet parents to consult with their family veterinarian or local veterinary medical oncologist to determine the best treatment plan. With the proper veterinary health care team in place, you can go from diagnosis to initiating treatment within little more than one week.

What treatments are available for canine lymphoma?

Numerous advances in veterinary oncology have been made over the last couple decades, improving survival times for canine lymphoma drastically. Systemic chemotherapy is the treatment of choice for canine lymphoma while still maintaining a good quality of life. Fortunately, pets will experience fewer and less severe side effects from chemotherapy compared to humans. This benefit is due to the lower doses and less intense dosing schedules used in pets. 

Many different drugs have been utilized either alone or in combination for the treatment of lymphoma in dogs. Combination chemotherapy has been reported to result in response rates up to 96% with prolonged remission (215 to 250 days) and survival durations of approximately one year. Some of the different drugs used include: L-asparaginase, vincristine, cyclophosphamide, doxorubicin, and prednisone. While combination chemotherapy is currently the treatment of choice, bone marrow transplants are available at select facilities and future treatment may include immune therapy with vaccines.  

Your veterinary medical oncologist will work with you to determine the best treatment plan that fits your ideal balance of quality of life, expected remission and cost. During treatment, regular monitoring and checkups are required for evaluating the patient’s response. Plans remain flexible and are adjusted as necessary throughout treatment to best meet the goals of both the patient and the pet parent. 

What is the prognosis for dogs with lymphoma?

Overall, canine lymphoma is a very treatable condition. It is important to realize that the treatment goal is not for a cure, but instead for high-quality, disease-free time to be added to the patient’s life. Most pet parents are very happy with the clinical outcome and response to therapy. While combination therapy survival rates average around one year, approximately 20% of dogs survive more than two years with currently available treatments.

What is chemotherapy like in dogs?

Chemotherapy in dogs is very different than chemotherapy in people. This is because your veterinary medical oncologist will tailor a treatment plan utilizing lower drug doses over a longer period of time to minimize side effects. Most dogs undergoing treatment for lymphoma experience no or minimal side effects and can continue with their typical routine.

Edited by: 
Gabrielle Angelo DVM, DACVIM (Oncology)
April, 2020