New Treatment Option for Lymphoma in Dogs

Published Oct. 23, 2013

I’ve just returned from Minneapolis after attending the Veterinary Cancer Society’s (http://www.vetcancersociety.org) annual conference and wanted to share an exciting new treatment option for dogs with cancer.

The Veterinary Cancer Society (VCS) is a professional organization dedicated towards advancing cancer care for pets and includes a membership of over 800 specialists in medical, surgical, and radiation oncology plus internists, pathologists, pharmacologists, general practitioners, interns, and residents. Once a year we all gather to attend dozens of presentations on the ongoing research studies at various institutions throughout the world for pets with cancer.

Topics vary, but typically include clinical trials, retrospective studies, and basic science experiments. This year’s conference was heavily centered on the latter. For oncologists such as myself working in private practice, science experiments, though interesting, are hardly practical for me in my day-to-day endeavors. It takes a great deal of time to translate what goes on in petri dishes to practical use in the veterinary hospital, but it’s good to keep current, nonetheless.

However, such research is exactly what led to the development of this new treatment I am excited to discuss, highlighting its importance, even when the immediate relevance is not apparent.

One of the most interesting take-home points I had from the conference (other than figuring out how to get from my hotel to the conference site without ever having to step outside, using the city’s strange, but useful, skywalk system!) was the development of a promising new therapeutic option for B-cell lymphoma in dogs. This treatment is modeled off of a similar drug used in people with non-Hodgkin’s lymphoma called Rituximab.

I’ve discussed lymphoma in dogs in previous articles on this site, but as a quick recap, lymphoma is a cancer of lymphocytes, which are immune cells usually responsible for fighting off infections.

In people, lymphoma is usually classified as being 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 our canine patients is very similar to the DLBCL seen in humans.

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

The idea of developing “targeted therapies” for treating cancer has been around for decades, but it wasn’t until the late 1990s before 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; 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 very specific form of treatment for cancers (and other disorders) of B-lymphocytes, with limited toxicity to other tissues.

For humans with DLBCL, the addition of Rituximab to traditional CHOP chemotherapy regimens essentially resulted in achievable cure in many cases, and this combination is now accepted worldwide as standard of care for treating this form of lymphoma in people. Adding Rituximab to combination 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.

A logical question would be, why not try Rituximab to treat canine lymphoma? This exact experiment was performed several years ago. However, results were disappointing, as it was hypothesized that the engineered antibody was specific only for human CD20 and did not appear to recognize the canine version of this same protein. Since that time, the veterinary oncology world has anxiously awaited an animal-approved version of Rituximab to be discovered and developed.

The upshot from the conference is it appears that day is coming soon, possibly even as soon as the “very near future,” although frustratingly we were not offered specifics as to the “when and where” of an anticipated release date or even much information as to the efficacy of the product in dogs. It’s important to note that rituximab will likely not replace traditional chemotherapy for dogs with lymphoma, but will be an additional option we can use to extend the lives of our patients.

It’s difficult to remain patient knowing this option is “out there” but is not something I can immediately prescribe, but I am looking forward to being able to offer this treatment for my patients, and will certainly keep my eyes and ears open for its release.