In the Battle Against Cancer, ‘Targeted Therapies’ Are Evolving from Human to Animal Medicine

Published Aug. 19, 2015

Lymphoma is the most common cancer diagnosed in dogs and cats. It’s also an extremely common cancer in humans. This represents a unique opportunity where people can potentially benefit from treatment options developed for pets, and vice versa.

In people, lymphoma is usually classified as Hodgkin-like (HL) or Non-Hodgkin-like (NHL), with NHL being the most common form. Diffuse large B-cell lymphoma (DLBCL) is the most common form of NHL in people. Though many different forms of lymphoma exist in dogs, the most common form we diagnose in canine patients is similar to the DLBCL seen in humans.

Traditionally, in both people and animals, NHL is treated with chemotherapy using cytotoxic drugs in what is known as the “CHOP” protocol. The chemotherapy drugs in this protocol, though effective, are not specific for cancer cells, and this is the main reason for the adverse side effects seen with treatment.

The idea of using “targeted therapies” as anticancer weapons is not new, but it wasn’t until the late 1990s that this idea became a reality. Targeted therapies are designed to do exactly what their name implies: specifically target cancer cells while sparing healthy cells, thereby reducing side effects and, hopefully, also increasing efficacy.

Rituximab is an example of a targeted therapy in people; it is a “manufactured” antibody directed against a protein located on the outer surface of B-lymphocytes called CD20. After administration, one end of the rituximab antibody binds to the CD20 protein while the other end “sticks out” and signals the patient’s immune system to attack the lymphocyte and destroy it. Rituximab will bind to both cancerous and normal B-lymphocytes, but not to cells of other healthy tissues. making it a specific form of treatment for cancers (and other disorders) of B-lymphocytes, with limited toxicity to other tissues.

For humans with DLBCL, the combination of rituximab with traditional CHOP chemotherapy regimens essentially resulted in achievable cures in many cases, and this combination is now accepted worldwide as the standard of care people with lymphoma. Rituximab in combination with chemotherapy during the initial treatment of less aggressive variants of B-cell lymphoma (other than DLBCL) has also been documented in multiple clinical trials over the past decade.

Rituximab, unfortunately, is an ineffective treatment for canine lymphoma. The engineered antibody is specific only for the human version of CD20; it does not recognize the canine version of this same protein. However, the exciting results seen in people prompted intensive research towards developing monoclonal antibodies that would be effective for dogs.

After many years of study, several pharmaceutical companies have produced B-cell and T-cell monoclonal antibodies for use in dogs, and the veterinary oncology world is on the cusp of having such therapeutics available for widespread commercial use. Preliminary studies show the antibodies are safe and reasonably effective for the treatment of canine lymphoma. Studies are ongoing to determine the optimal timing of treatment, long-term benefit, and to better characterize any adverse effects.

Investigational studies examining the use of these therapeutics in greater detail are available at select veterinary hospitals across the United States. For example, the hospital where I work is one of only a handful of sites chosen to offer the T-cell monoclonal antibody as a treatment option for their patients.

If you would like to find out more information about monoclonal antibody therapy for your dog with lymphoma, please ask your veterinarian or contact your local veterinary oncologist for further information.