Stages of Treatment for Cancer in Pets

By Joanne Lynn Intile, DVM, MS, DACVIM on Oct. 17, 2012

Last week I introduced you to Casey, an imposing, yet very friendly, Great Dane diagnosed with lymphoma about a year ago. Casey underwent six months of chemotherapy treatments for his disease and is currently doing very well at home.

He spent his summer swimming in his owner’s pool and lounging on patio furniture with his "sister," an equally imposing Dane weighing in at a mere 150lbs. Since lymphoma is such a common cancer diagnosed in dogs and cats, I wanted to spend time providing some basic information on this disease and reviewing the important points I discuss with owners during a typical initial appointment.

Lymphoma is a blood-borne cancer of lymphocytes, the white blood cells typically involved in fighting off infections. These cells generate antibodies designed to provide long-term immunity against the various pathogens animals (and people) are exposed to during their lifetime.

Certain breeds of dogs and cats develop lymphoma more frequently than others, indicating a genetic susceptibility to this type of cancer. Studies regarding environmental causes of lymphoma are conflicting, especially with regard to exposure to environmental herbicides, household or agricultural chemicals, environmental tobacco smoke, and/or electromagnetic radiation. Dogs living in industrial areas where certain chemicals are common tend to have a higher incidence of this disease. In cats, infection with the FeLV or FIV virus is associated with increased risk of development of lymphoma.

When a dog or cat is diagnosed with lymphoma, the first thing I discuss with the owner(s) is something called staging. Staging refers to performing various tests designed to determine where in their pet’s body we see evidence of disease. Since lymphoma is a blood borne type of cancer, it is typically present in multiple anatomical areas at the time of diagnosis. What I try to stress to owners is that this is not the same thing as a tumor that starts growing in one region and spreads (metastasizes) to other parts of the body. This means I don’t panic when we test a pet and find evidence of lymphoma within many different regions. What matters more to me are the specific anatomical sites that are involved.

For example, it is relatively common to find lymphoma within internal lymph nodes of the abdomen or chest when performing staging tests, but it would be uncommon to see involvement of the stomach or intestinal tract. I am definitely more concerned if the latter is seen within one of my patients, as this typically indicates a more aggressive clinical course of disease and a more guarded prognosis.

After discussing the staging tests, we then move onto talking about treatment options. During this part of the consult, I try to stress to owners that lymphoma is a very treatable disease in dogs and cats. Most cases of lymphoma are best treated with chemotherapy. However, there are some cases where surgery and/or radiation therapy (either with our without chemotherapy) would be ideal. There are many different chemotherapy drugs that can be effective for treating lymphoma, and often I discuss several different options with owners in order to find what works best for their pets and their own lifestyle.

I typically recommend a multi-agent protocol of injectable chemotherapy drugs for treating the most common form of lymphoma in dogs and cats. With this protocol, we are extremely successful in having our patients achieve what is known as a remission. This means that all visible, detectable evidence of their disease disappears with treatment. Remission is not the same things as a cure, however, and for the vast majority of patients, at some point their cancer will return.

Though we are not expected to cure our patients, we are able to provide them with an excellent quality of life during treatment, and for the average dog, for several months following completion of their chemotherapy protocol. For example, for dogs, survival times can vary, but typically are expected to be about one year from the time of their diagnosis, with 25 percent of dogs living two years. Side effects are uncommon, but very manageable should they occur.

Without treatment, this form of cancer is often rapidly progressive, and pets succumb within a few weeks to months from their time of diagnosis.

Fortunately, for many dogs like Casey, we are able to successfully control their lymphoma for many, many months and provide their families more time and happy memories with their pets.

We are all hopeful that a cure is on the horizon, but until then I’ll continue to help pets and their owners continue to enjoy their bond, even in the face of a devastating diagnosis.