There’s no getting around it: It’s a stomach churning moment when you hear the word “lymphoma” regarding your dog. This fairly common cancer affects the body’s lymphocytes, the white blood cells that are part of the lymphatic system. Veterinary science is working to determine the cause of this type of cancer, but to date, no definitive cause has been established.
B-Cells and T-Cells
All lymphocytes are instrumental in the body’s defense system, but not all lymphocytes are alike. These white blood cells come in two primary subgroups: B-cells and T-cells. According to Dr. Wendy Brooks of VeterinaryPartner.com, 75 percent of canine lymphoma originates in the B-cell lymphocytes. That’s good news because B-cells tend to be more responsive to lymphoma treatment protocols than T-cells are. It appears T-cell lymphocytes seem to deteriorate quicker; the Merck Manual for Veterinary Medicine states the expected survival time for dogs with B-cell lymphoma is approximately 12 months, compared to the six-month survival time associated with T-cell lymphoma.
Types of Lymphoma
In addition to variation in the origin of lymphocyte, lymphoma can differ in the form it presents in. Multicentric lymphoma, when the cancer is first obvious in the lymph nodes, is the most common type of lymphoma in dogs. In this form of lymphoma the lymph nodes are obviously enlarged. It usually presents as lumps under the chin. Since the lymphocytes are affected in lymphoma, it’s normal for organs in the body’s immune system to be affected, including the spleen and bone marrow as well as the lymph nodes. However, any body part can be affected by lymphoma, accounting for the other forms of lymphoma: gastrointestinal, which is cancer of the intestinal tract; mediastinal, occurring in the chest and extranodal, presenting in the skin, eye and other areas.
Though it’s not known why, a few breeds tend to have a higher incidence of lymphoma. Basset hounds, Saint Bernards, bulldogs, boxers, Scottish terriers, Airedales and bull mastiffs are among the breeds that appear to be predisposed to the disease, while dachshunds and Pomeranians seem to have a lower risk of developing lymphoma. It’s seen more frequently in dogs between 6 and 9 years of age; spayed females tend to fare better in treatment.
No Known Cause, No Known Prevention
Despite ongoing research, at present, there’s no definitive causal link between environment and canine lymphoma. Some studies show a predisposition to lymphoma based on exposure to herbicides, paints and other chemicals. As well, dogs with weak immune systems appear to have greater risk of developing lymphoma. Given that some breeds have a higher incidence of the disease, there may be a genetic correlation, though that hasn’t been proven. The dog diagnosed with lymphoma has no one to blame, and currently, there’s nothing an owner can do to prevent lymphoma.