Lymphoma - Dog

Lymphosarcoma is a common cancer of lymphocytes in dogs and 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 lymphomas?

Lymphomas primarily affect middle age to older dogs. There does not appear to be a breed or sex predilection. Only 10% to 20% of dogs are clinically ill at presentation, the majority are brought in 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. Some authors have speculated that environmental factors such as exposure to pesticides or strong magnetic fields increase the incidence, but there is currently no strong proof of this. At the same time, some authors have also hinted at a possible genetic correlation, but further studies need to be performed to determine the exact risk factors involved in canine lymphoma.

What are the symptoms of lymphoma?

The symptoms of lymphoma are related to the location of the tumor(s). Tumors that develop in the lymph nodes often present as swellings with no other symptoms. The gastrointestinal form often is accompanied with vomiting, diarrhea, weight loss and lack of appetite. 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.

How is lymphoma diagnosed?

Lymphoma 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 of lymphoma. The exact tests performed will depend on the location of the tumor.

What is the treatment for lymphoma?

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 practitioner. The University of Wisconsin protocol is one of the more popular ones used by veterinary oncologists. While most veterinarians can administer the treatment protocols, I always recommend that the owners of a dog with lymphoma initially 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 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. I often remind clients that one year can be almost 10% of a dog’s expected life span, so the remission rate and increased life expectancy with lymphoma treatment is often well worth it.

References

Ettinger, S; Feldman, E. Veterinary Internal Medicine 5th Edition. Published by Saunders. Philadelphia; 2000.

Bonagura, J; Kirk, R. Current Veterinary therapy 12. Published by Saunders. Philadelphia; 1995.

DVM, Villalobos A. Canine Lymphoma Treatment Options. Veterinary Practice

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