Lymphoma in dogs is a common cancer of lymphocytes. Between 15% and 20% of malignant tumors in dogs are lymphomas. Lymphomas can occur in the lymph nodes, spleen, liver, and other organs. The cancer can be aggressive and if left untreated, can lead to a high mortality. Treatment with chemotherapy has been very successful, adding months and occasionally years to the dog's life.
Which dogs are at risk for developing lymphoma?
Lymphoma primarily affects middle age to older dogs. There does not appear to be a sex predilection. Golden retrievers, boxers, bullmastiffs, basset hounds, Saint Bernards, Scottish terriers, Airedales, and bulldogs appear to be at increased risk of developing lymphomas. Only 10% to 20% of dogs are clinically ill when diagnosed; the majority are brought to the veterinarian because of recently identified swellings or lumps.
Why do dogs develop lymphoma?
While we understand how lymphomas form, we still do not understand why. In cats, there appears to be a strong link between some forms of lymphoma and infection with feline leukemia virus, however, in dogs such a link is not apparent. At the same time, some authors have hinted at a possible genetic correlation, but further studies need to be performed to determine the exact risk factors involved in canine lymphoma. Dogs who have a suppressed immune system appear to be at increased risk.
What are the symptoms of lymphoma?
The symptoms of lymphoma in dogs are related to the location of the tumor(s). Tumors that develop in the lymph nodes often present as swellings with no other symptoms. When the lymphoma is present in the gastrointestinal tract, vomiting, diarrhea, weight loss, and lack of appetite are commonly seen. The mediastinal (chest) form often presents with shortness of breath and muffled heart sounds. The cutaneous (skin) form can present in several different ways including single or multiple lumps in the skin, or mouth. These bumps can itch or be red and ulcerated. Lymphoma can also occur in the heart, eyes, central nervous system or bone.
How is lymphoma in dogs diagnosed?
Lymphoma in dogs is diagnosed with a combination of diagnostic tests. Blood tests, fine needle aspirates of the tumor, biopsies, x-rays, and ultrasound are all used to confirm the diagnosis and location(s) of the lymphoma. The exact tests performed will depend on the location of the tumor. A complete blood count, chemistry panel, and urinalysis are also recommended. Lymphoma generally does not cause pain unless there is bone involvement. In 15% of dogs with lymphoma, the blood calcium level will be high.
The World Health Organization has developed a staging system for dogs with lymphoma. The stage is used in determining treatment regimens and prognosis. The stages are:
- Stage I: Single lymph node involved
- Stage II: Multiple lymph nodes in the same region involved
- Stage III: Multiple lymph nodes in multiple regions involved
- Stage IV: Liver and/or spleen involved (may or may not have lymph node involvement)
- Stage V: Bone marrow or blood involvement and/or other organ besides liver, spleen and lymph nodes involved
Dogs are further classified as "substage a" if they are not showing signs of illness, and "substage b" if they are.
What is the treatment for lymphoma in dogs?
The treatment for lymphoma in the dog consists of chemotherapy. Lymphoma is considered a systemic disease, which makes surgery and radiation impractical and ineffective. There is a wide variety of chemotherapy protocols and drugs that are currently being used to treat lymphoma. The treatment usually consists of a combination of oral and injectable drugs given on a weekly basis. Some commonly used drugs include cyclophosphamide, vincristine, doxorubicin, and prednisone. The exact treatment protocol will vary depending on the veterinarian. The University of Wisconsin protocol is one of the more popular ones used by veterinary oncologists. While most veterinarians can administer the treatment protocols, owners of a dog with lymphoma may initially want to seek out a consultation with a veterinary oncologist to inform themselves of any new treatment recommendations.
What is the long-term outlook for a dog with lymphoma?
Some owners choose not to treat dogs that develop lymphoma. The life expectancy of these untreated dogs with generalized lymphoma (Stage III, IV, or V) averages 4 to 6 weeks. Oral prednisone therapy may reduce the swellings and discomfort, but probably will not appreciably extend their life span. It must also be noted that oral prednisone treatment prior to chemotherapy is not recommended and may actually reduce the effectiveness of the chemotherapy.
In dogs that do undergo one of the recommended chemotherapy protocols, life expectancy can extend out to a year and occasionally longer. However, even dogs that receive appropriate chemotherapy usually do not live longer than a year. If a dog tolerates chemotherapy (most dogs do) their quality of life can be quite good during the treatment period. Treatment for lymphoma in the dog is considered one of the more successful cancer treatments and can often be performed by a local veterinarian without the need to travel long distances to veterinary schools or specialty clinics. Since one year can be almost 10% of a dog's expected life span, the remission rate and increased life expectancy with lymphoma treatment is often well worth it.