Canine lymphoma is one of the most common cancers diagnosed in dogs today, accounting for up to 24% of all new canine cancers. It is a cancer of lymphocytes (a type of white blood cell) and lymphoid tissues. Lymphoid tissue is normally present in many places in the body, including lymph nodes, spleen, liver, digestive tract, and bone marrow. In most cases, we do not know what causes lymphoma. The most common form of lymphoma in dogs is the involvement of one or more of the external lymph nodes.
Recognizing the Signs of Lymphoma in Dogs
Symptoms of lymphoma may be difficult to identify. Many dogs may not feel sick or may have only very mild signs such as tiredness or decreased appetite. Other dogs may have more severe symptoms such as weight loss, vomiting, diarrhea, excessive thirst or urination, weakness, or difficulty breathing. The severity of the signs depends upon the extent of the disease and on whether the cancer has caused changes in organ function. Often, the only noticeable sign is an enlargement of the lymph nodes under the neck, behind the knees, or in front of the shoulders. Organs, such as the liver, spleen, and bone marrow can be involved as well.
Diagnosis and Evaluation of Canine Lymphoma
When lymphoma is suspected, the patient will receive a complete evaluation, including a biopsy or needle aspirate of the affected tissues and a search for lymphoma in other locations (called staging). A complete blood count (CBC), a serum chemistry profile, and urinalysis are performed and provide important information regarding the effects of the cancer on body functions as well as the ability of the patient to handle chemotherapy. Chest X-rays allow veterinarians to look for enlarged internal lymph nodes or lung involvement. A bone marrow aspirate looks for lymphoma cells infiltrating the bone marrow and evaluates the marrow’s ability to produce normal blood cells. Special molecular tests can be applied to lymphoma tissue to determine the cell of origin of the lymphoma (B cell vs. T cell). Once veterinarians have these results, they can provide a more accurate idea about the outcome with various types of treatment. However, completing all staging tests is not a requirement for treatment of dogs with lymphoma.
Treatment and Prognosis for Canine Lymphoma
Chemotherapy is the mainstay of treatment for lymphoma. Lymphoma is very sensitive to chemotherapy, and up to 95% of dogs treated will go into remission when the most effective treatment protocols are used. The definition of remission is the complete disappearance of all signs of cancer. A remission is NOT a cure, but it does allow your pet to experience a good quality of life. It is important to remember this because a chemotherapy protocol should not be discontinued as soon as remission is achieved. The length of remission depends upon many factors, including the primary site, how sick an animal is at the start of treatment, blood calcium level, B cell vs. T cell origin, and presence of lymphoma in the bone marrow. For those dogs that have the most common type (external lymph nodes enlarged) and one with the most aggressive treatment protocol, the average survival time is about one year; approximately 20% of dogs may live longer than two years.
There are several different treatment options to consider, depending upon owner preference, how aggressive the cancer is behaving, how sick an animal is at the start of treatment, and any abnormalities in organ function (especially significant are changes in liver and kidney function). On a typical schedule, a patient will receive weekly treatments for approximately four months. Several different drugs (vincristine, cyclophosphamide, and doxorubicin) are alternated to reduce the chance that the tumor cells will become resistant and lessen the risk of side effects. If a patient remains in remission after 4-6 months, treatment is discontinued, and monthly rechecks are scheduled to ensure that remission persists. If and when the disease returns, the same drugs are often effective again, although the duration of remission is often shorter.
Canine Lymphoma Clinical Trials
Clinical trials offer another treatment option. The Flint Animal Cancer Center currently offers five clinical trials to study new treatments for canine lymphoma. Most families who participate in FACC clinical trials live within 150 miles of Fort Collins or are willing to travel or temporarily relocate for the period of the study. The main goal for every patient is a good quality of life. Clinical trials related to pet cancer are conducted throughout the United States. If you do not live close enough to participate in a FACC study, please visit AVMA to search for trials in your area.
If you have concerns about your pet’s health or notice any of the symptoms mentioned above, contact your pet’s veterinarian.