Lymphoma in the Dog

The lymphatic system, including the lymph nodes and the spleen, is extremely important in the body’s immunologic defense against “foreign” invaders, known as “antigens”. The lymph nodes contain numerous types of white blood cells that are important in the body’s fight against infection. The role of the lymph nodes, as a result, is to filter circulating material and aid in the removal of unwanted antigens.

Lymph nodes are located in various areas throughout the body, some that can be easily located and some that are deeper within the body, requiring imaging techniques in order to be identified. Lymph nodes filter material from tissues and check for things that should not be there, such as bacteria and viruses. Lymph nodes can be enlarged for several reasons: in response to antigen stimulation (such as a bacterial infection), in the case of an infection of the lymph node itself, or in cases of a cancer such as lymphoma.

During a physical exam, your veterinarian will assess the size of your dog’s accessible lymph nodes to determine whether further investigation is required.

A normal immune response to an infectious organism, such as a bacterium, can result in the recruitment of more cells to help with the battle. The increased number of cells causes a temporary increase in size in the lymph node closest to the source of the infection. In this case, the enlarged lymph node should return to its normal size once the infection has cleared. Another way a lymph node can be larger than normal is if there is an infection of the lymph node itself, called “lymphadentitis”. The lymph node is usually hot, swollen, and painful. Finally, a lymph node can increase in size if cancerous cells have replaced normal cells, most commonly observed in a neoplastic condition called “lymphoma”. Animals that have lymphoma commonly present with many of their lymph nodes greatly enlarged, often first noticed as unusual bumps on the animal’s body.

Predisposition to lymphoma seems to have a genetic basis, as some breeds of dogs are more commonly affected. These include, but are not exclusive to Rottweilers, Cocker Spaniels, Golden Retrievers, Boxers, and Basset Hounds. Most dogs develop lymphoma later in life, usually between six and twelve years of age. Often, there is no history of illness and the only signs of disease are the enlarged lymph nodes. Other times, non-specific signs such as weight loss, lethargy and a loss of interest in food may be noticed. Although the lymph nodes are the tissue most commonly affected, the brain, eye, lungs, skin and/or gastrointestinal tract can also be affected.

Diagnosis of lymphoma can oftentimes be a difficult task, requiring the use of many different tests to rule out other common diseases. Your veterinarian will collect blood and urine to check for abnormalities, signs of other diseases, and to assess organ function. This is important to not only to rule out other diseases for a proper diagnosis, but also to evaluate the animal’s state of health before treatment. Radiographs and ultrasound may also be used to look for lymphoma in places that cannot be assessed readily during a physical exam, such as lymphoma affecting the spleen or gastrointestinal tract. Finally, samples of the affected lymph nodes or organs will be taken and viewed under a microscope for cancerous cells.

Treatment of lymphoma is not an easy process and not for the faint of heart. Treatment is demanding both physically to the animals and financially to the owner. However, new treatment protocols have been very successful in extending an animal’s survival time, while preserving the quality of life. While the estimated survival time for patients without treatment is between four and eight weeks, the average survival time with treatment is between twelve and sixteen months. The standard of care in dogs is a combination of chemotherapy drugs, used both to increase efficacy and reduce the side effects of the drugs. Almost 85% of all cases can achieve remission, so the prognosis for an increased survival time is quite good.

Lymphoma can be a devastating diagnosis and is one of the most common cancers diagnosed in dogs. However, with today’s advances in medical care, treatments are readily available and most dogs and their humans can look forward to many more enjoyable months together.

By Beverly Wong – Pets.ca writer