Canine Lymphoma

Cancer of the lymphatic system is a common cancer in dogs. Lymphoma is considered a cancer of the immune system because the lymphocyte, which is the affected cell, plays an important role in defense of the body against infections. Lymphoma can rapidly ruin the health of the internal organs and without treatment can become life threatening to the pet within four to eight weeks. While any dog may develop lymphoma, Golden Retrievers, Boxers, Labrador Retrievers, Rottweilers, St. Bernards, Airedale Terriers, Bulldogs, and Basset Hounds are commonly affected. The cause of lymphoma is unknown, although there is an increased risk in dogs exposed to herbicide 2,4-D.1 Pups as young as 4 months of age are seen with lymphoma, but 80% of cases are seen in 5- to 11-year-old dogs. The relative risk is significantly higher for boxers. Older dogs tend to survive longer than younger dogs.3

While lymphoma can involve any organ in the body, most commonly the lymph nodes are affected. Owners may notice a painless enlargement of the pets lymph nodes; fever is typically absent, and most dogs do not feel or seem sick, unless there are some other problems, such as elevated blood calcium. These signs are usually observed in dogs with multicentric lymphoma, the most common type of lymphoma in the dog. Sometimes the affected lymph nodes will enlarge, then regress to normal size, then enlarge again. With alimentary lymphoma, affected dogs will show weight loss and often have diarrhea. Because lymphatic system is located alongside the vascular system (bloodstream), lymphoma is considered a systemic (whole body) disease and may strike in any location, including skin. Some dogs develop enlargement of other lymphatic organs, such as the thymus gland, spleen, and liver. Occasionally, lymphoma will affect a dog's bone marrow or central nervous system.

However, cutaneous (skin) lymphoma is relatively uncommon. It can be divided into nonepitheliotropic and epitheliotropic forms. The nonepitheliotropic lymphoma is a mixed group of T and B cells lymphoma which produce infiltrates growing in the deep dermis or subcutis. Epitheliotropic lymphoma is a subset of cutaneous T cell lymphoma and is the most common form of cutaneous lymphoma. Affected dogs have chronic dermatitis, peeling of the skin, plaques or nodules, ulcerative disease of the oral surfaces. Lesions are most commonly seen over the trunk (83.3%) or localized to the head (63%) and the footpads. Itching is observed in 40% of cases. Several therapies have been evaluated for the treatment of cutaneous lymphoma, but complete recoveries are rare.3

Diagnosis is obtained by aspiration cytology of the affected organ, usually a lymph node, and biopsy. The treatment goal is to get a remission and to keep it as long as possible. Ideally, the first remission lasts for 6 to 12 months. There are many good options for managing lymphoma and inducing remission for as long as possible while also providing for the best quality of life.1 Lymphomas are classically treated with chemotherapy. Since dogs are treated less aggressively, there are usually fewer side effects than in humans. Single chemotherapy drugs such as doxorubicin may add 6 to 12 good months to your dog's life. Combination protocols (mixes of chemotherapy drugs in a carefully planned dosage) can keep dogs cancer free for up to 3 years. Inductions protocols use high levels of very strong drugs to knock the cancer down dramatically right at the start. This minimizes the chances of cells developing drug resistance. A maintenance protocol may use different drugs, lower dosages, or less frequent treatments.2 Surgery plays almost no role in controlling the cancer.

References

  1. The Natural Vet's Guide to Preventing and Treating Cancer in Dogs. Shawn Messonnier
  2. Cancer and your pet: the complete guide to the latest research, treatment. Debra Eldredge, Margaret H. Bonham
  3. Tumors in domestic animals. Donald J. Meuten
  4. Protein 53 expression in a mixed Labrador subcutaneous lymphoma Annahita Rezaie1,* and Abbas Tavassoli2 Vet Res Forum. 2012 Spring; 3(2): 147–149.