Lymphoma is a very common type of cancer in both dogs and cats, and we treat both at Arizona Veterinary Oncology. The exact cause in unknown, and there are likely many reasons, but in dogs there may be a genetic predisposition in some breeds such as Boxers, Golden Retrievers, and Bulldogs. The median age of affected dogs is 6 to 9 years. Lymphoma arises from blood cells (lymphocytes), usually in lymphoid tissues such as lymph nodes, spleen and bone marrow, however it can arise in almost any tissue in the body. Most lymphomas in dogs are high grade and the majority of cases involve primarily the lymph nodes, but it can also involve only the liver and spleen, the gastrointestinal tract, the mediastinal lymph nodes (in the front part of the chest), or the nasal cavity. Initial clinical signs will vary depending on where the lymphoma originates, with most dogs presenting with enlarged lymph nodes. Most of the time, this is recognized as lumps under the jaw or behind the knee. In most cases a diagnosis can be made by doing aspirates of affected organs to collect samples for cytology, however, occasionally additional diagnostics are required. Aspirates involve inserting a needle into the mass and removing some cells. The cells are placed on a microscope slide, stained and reviewed by your oncologist and/or an outside laboratory. This process is referred to as cytology. Your friend can often be awake for this process and there is little discomfort involved (much like getting a vaccination). Staging (finding out where in the body the cancer is) of lymphoma involves lab work, chest X-rays and an abdominal ultrasound in order to evaluate the full extent of disease. Immunophenotyping is a special test that may also be done to determine if your dog has B- or T-cell lymphoma, which is based on which type of lymphocyte the cancer originated from. Dogs with B-cell lymphoma carry a better prognosis than dogs with T-cell lymphoma, however, dogs with T-cell lymphoma can also go into remission for several months. In most cases the treatment of choice for lymphoma is chemotherapy, as it considered a systemic (throughout the body) disease. For dogs and cats with nasal lymphoma, radiation therapy can be used alone, or in combination with chemotherapy. Chemotherapy is very well tolerated by most dogs. The majority of dogs have no to minimal side effects, and experience a very good and normal quality of life. The most effective chemotherapy protocol for lymphoma is a 6 month, multi-drug, chemotherapy protocol. Treatments are once a week for the first 2 months, then every other week through the end of the protocol. About 85 to 90% of dogs will go into remission (no evidence of the cancer) with this protocol. For dogs with enlarged lymph nodes we typically assess remission status by monitoring the size of the lymph nodes, but for dogs with other types of lymphoma, intermittent imaging may be recommended (eg an abdominal ultrasound to look at the liver and spleen). Studies show that the average time your pet will be in remission the first time is eight to ten months. This includes the time while chemotherapy is being given. With this protocol, about half the patients will live one year and about 20% will be alive at two years. If/when dogs come out of remission, many can restart chemotherapy in the hopes of once again getting them back into remission. Sometimes the same chemotherapy protocol is used and sometimes a different drug or drugs will be used. This can help extend their life longer as well. Many options for chemotherapy exist that involve different schedules and costs. Your oncologist will help design the perfect protocol for you and your furry friend that fits your schedule and financial situation.
Lymphoma is also seen commonly in cats. As in dogs, in most cats there is no specific cause, however, cats that are positive for the feline leukemia (FeLV) or feline immunodeficiency Virus (FIV) are at increased risk. Lymphoma in cats can be high grade or low grade, and most frequently involves the gastrointestinal tract. Clinical signs most commonly include lethargy, weight loss, decreased appetite, nausea, and/or diarrhea. Cytology can confirm a diagnosis in some cases, but often in cats, biopsies of the affected area are needed for a definitive diagnosis. As with dogs, most cases of lymphoma in cats require chemotherapy as the treatment of choice. The ideal protocol will depend on whether the lymphoma is high or low grade. Cats also tolerate chemotherapy extremely well, with no to minimal side effects. The most common side effects in cats are mild lethargy and a decrease in appetite for a day or two after treatment. The most effective treatment for high grade lymphoma is the same multi-drug chemotherapy protocol that is recommended in dogs with high grade lymphoma (see above). About 70% of cats with high grade lymphoma will go into remission with this protocol and the median survival time is about 8 to 10 months. Low grade lymphoma is treated with an oral chemotherapy called chlorambucil, in combination with prednisolone, a steroidal anti-inflammatory medication. Steroids have also been shown to be beneficial in the treatment of lymphoma. These drugs are given orally at home, in most cases for as long as your cat is feeling well. Regular exams and lab work are required to ensure your pet is feeling well and not having any complications related to the medications. About 75% of cats with low grade lymphoma will achieve a complete or partial remission and improved clinical signs resulting in a normal quality of life. The median survival time is about 18 to 24 months. In both high grade and low grade lymphoma of the GI tract, intermittent abdominal ultrasounds are often recommended to objectively monitor disease status.
While not curable, lymphoma is a very chemotherapy-responsive disease. Both dogs and cats can experience a good quality of life for months to years with treatment. At Arizona Veterinary Oncology, treating cancer is all we do. More good days are what we always strive to help your family achieve. If you have other questions, we encourage you to write them down and bring them to your consultation where they will all be answered. We look forward to meeting you getting your pet on the road to feeling better.