Q: My dog was just diagnosed with lymphoma. My vet recommended chemotherapy. I heard that chemotherapy is different in dogs than it is in people. Is this true?
A: I am very sorry to hear about your dog. Lymphoma is one of the most commonly diagnosed cancers in dogs. It is a cancer of lymphocytes, a type of white blood cell and part of the immune system. The immune system is throughout the body, and consequently lymphoma often involves multiple sites throughout the body. The most commonly affected sites are the lymph nodes, liver, spleen, and bone marrow, but almost any site in the body can be affected.
Before starting any therapy, your veterinarian likely will recommend that some staging diagnostic tests be performed. The purpose of clinical staging is to determine the extent of the cancer in your dog’s body, identify any unrelated diseases that might impact treatment decisions, and assess overall health. Staging information guides treatment recommendations, helps to more accurately assess response to therapy, and provides useful prognostic information. (There is a numeric staging system used for canine lymphoma, with stage I being the least advanced and stage V the most. However, the number itself has relatively little prognostic significance for this particular cancer.)
The treatment for canine lymphoma typically involves chemotherapy. This disease rarely affects only one location or organ, and therefore drugs that circulate throughout the body are most effective. Surgery and radiation therapy play very limited roles in the treatment of this cancer. The chemotherapy drugs used to treat canine lymphoma are also used to treat non-Hodgkin’s lymphoma in people. There are several different published chemotherapy protocols, and deciding which to use will depend on several factors: staging test results, clinician preference, and family-based factors (frequency of visits, length of protocol, cost). Your veterinarian likely will discuss several different treatment options along with the advantages and disadvantages of each.
Chemotherapy treatment in dogs is very different than chemotherapy treatment in people. Yes, for the most part the same drugs are used, but there are two very important differences. First, the drug dosages are much lower, even when taking into consideration differences in body size between people and dogs. Second, in veterinary oncology not as many drugs are given at the same time; instead, we usually space them out on a rotating basis. As a result, adverse effects from treatment are less frequent and usually are muchless severe.
The potential adverse effects depend on the specific drug(s) included in a given treatment protocol. However, the most common adverse effects seen are gastrointestinal (decreased appetite, vomiting, diarrhea). Only about 10% of dogs experience these effects, and when these signs do occur they usually are mild and resolve on their own within a day or so. For more pronounced gastrointestinal signs, there are very effective medications that often can help amelioratethem. If adverse effects are observed, future occurrences often can be prevented either by prescribing gastrointestinal supportive medications preemptively or reducing the dosage of a given chemotherapy drug. Again, maintaining quality of life throughout treatment is paramount.
The trade-off for fewer adverse effects is lower cure rates, but most oncologists (myself included) agree that quality of life is more important.Having said that, with our most effective treatment protocols, about 85-90% of dogs with lymphoma will attain a complete remission (defined as complete resolution of all signs associated with the cancer). About half of our patients will enjoy at least one year of excellent quality of life, and about twenty-five percent will enjoy at least 2 years of excellent quality of life. Less than five percent of dogs with lymphoma are ever truly cured (i.e., the cancer never recurs). Left untreated, canine lymphoma usually is fatal within 4-6 weeks of initial diagnosis.
The decision to pursue cancer treatment for a family pet is never easy. It is important to have as much information as possible before making any decisions. Questions you should ask your veterinarian include: What is the chance of the cancer responding to treatment? If the cancer does respond to treatment, how long is the response likely to last? What is the potential for any adverse effect from treatment? What is the potential for a severe adverse effect from treatment? If adverse effects do occur, are they reversible?I wish you and your dog all the best.
For additional general information regarding cancer in companion animals, I would recommend an on-line video published by the Cornell University College of Veterinary Medicine at the following website: http://partnersah.vet.cornell.edu/node/189.