A new option for the treatment of canine lymphoma
Non peer reviewed summary, 2/2002
Chand Khanna DVM, PhD, Dipl ACVIM (Oncology)
Animal Cancer Institute LLC

Lymphoma is the most common malignant cancer treated in veterinary oncology. In dogs, the most common presentation for lymphoma is multiple non-painful enlargements of peripheral lymph nodes. It is most common that dogs with lymphoma present without any clinical signs of illness in spite of these enlarged lymph nodes. In most cases lymphoma is thought of as a disseminated disease, where the malignant lymphocytes exist in many tissues through the body. The diagnosis of lymphoma is made by microscopic examination of lymph nodes. Unlike many other cancers, a diagnosis of lymphoma can be made using a fine needle aspirate alone. Microscopic features that distinguish malignant lymphocytes from normal lymphocytes include their larger size, multiple and variably sized nucleoli, and more frequent mitotic figures.

Treatment of Canine Lymphoma Treatment of Canine Lymphoma

Over time lymphoma will progress to involve both lymphoid and non-lymphoid organs. As the disease spreads and involves vital organs a progressive decline in quality of life is noted. The progression of this cancer often occurs quickly in dogs, but is quite variable. Lymphoma is one of the most chemo-responsive cancers in dogs. Dogs treated with chemotherapy can have a very high quality of life for many months to years. Dogs that feel well when therapy is initiated have the best chance of successful treatments. Dogs that respond well following the first one to two treatments often enjoy longer remission durations.

Options for the treatment of lymphoma include multi-agent chemotherapy, single agent chemotherapy, and prednisone alone. In addition, a new treatment is now available.

Multi-agent chemotherapy:
The use of multi-agent chemotherapy is expected to result in an initial complete regression (remission) of lymphoma in over 80% of dogs. On average this first remission will last for approximately one year. The return of the enlarged lymph nodes often marks the end of the remission. The following is an example of a multiple agent chemotherapeutic protocol used to treat canine lymphoma.

Canine Lymphoma Multi-Agent Chemotherapy Protocol (Khanna et al 1996 JAVMA). [insert table pic]

Canine Lymphoma Multi-Agent Chemotherapy Protocol

Single agent chemotherapy for lymphoma
Single agent chemotherapy protocols have been developed for lymphoma. Single agent therapies include doxorubicin, mitoxantrone and lomustine. Single agent doxorubicin chemotherapy is expected to provide a first remission rate that is similar to multiagent protocols and a first remission duration of approximately 7 months. Doxorubicin is administered as a single agent every 21 days for a total of 3 - 5 treatments.

Prednisone therapy for lymphoma
Prednisone alone may result in a regression of measurable lymph nodes in approximately 50% of cases. The duration of remission associated with prednisone has been reported to be 75 to 90 days. Prednisone doses for dogs with lymphoma are 40 mg/m2 daily.

The advantage of multi-agent chemotherapy for lymphoma is longer remission durations that result from the combination of drugs with different mechanisms of action. Although combination protocols have been designed to maximize quality of life, they are associated with a greater risk for toxicity tha single agent protocols. Clients who are concerned by the intensity of multi-agent protocols may be more comfortable with single agent therapies. Single agent therapies also have the advantage of being less expensive. Prednisone alone is often considered the best option for owners who are unable to consider chemotherapy due to financial restraints.

Recently a novel chemotherapy has become commercially available and is approved for the treatment of both pancreatic and lung cancer in people. This agent is in a class of chemotherapies referred to as a nucleoside analogue. Nucleoside analogue disrupt the synthesis of RNA in rapidly dividing cells. The activity of this new agent in canine cancer is largely anecdotal and unknown. We have treated a number of cancers in pet dogs using this agent, including lymphoma, soft tissue sarcoma, osteosarcoma, and hepatic carcinoma. The responses observed to date have been encouraging and suggest the need for further evaluation of this drug in pet dogs. Interestingly this agent has been associated with a very favorable toxicity profile in all cases treated to date. To determine if this new nucleoside analogue is effective in lymphoma a clinical trial has been designed and will open in April 2002 at a number of treatment sites in the United States. This trial is open for pet dogs with lymphoma that have not received prior chemotherapy. The trial provides all costs associated with diagnosis, treatment and follow up for dogs. This trial may be an ideal option for owners that are concerned about the side effects of conventional chemotherapy or find the costs associated with chemotherapy burdensome.

For more information about this clinical trial please contact Kate Cadorette.