Managing Canine Lymphoma
Lymphoma in dogs is one of the most common canine cancers our animal hospital diagnoses. Lymphoma is a cancer of the lymphocytes, which are a type of white blood cell and a part of the immune system. The function of lymphocytes is to help fight infection, and they can be found in almost any organ in the body, with the most common locations being the lymph nodes, spleen, and bone marrow. When a lymphocyte undergoes a mutation, it grows and multiplies uncontrollably and can cause the lymph nodes, spleen, or any other organ in which it is found to enlarge.
What are the Most Common forms of Canine Lymphoma?
There are several forms of lymphoma, with the most common being multicentric lymphoma. This form of lymphoma is represented by enlargement of the lymph nodes on the outside and inside of the body. Other forms of lymphoma include mediastinal (enlarged lymph node in the chest), cutaneous (skin), extranodal (bone, eyes, liver) and gastrointestinal (also called alimentary lymphoma). Multicentric lymphoma is by far the most common and comprises around 80% of diagnosed canine lymphomas, while the other forms of lymphoma represent about 5% each.
Unfortunately at this time, the cause for lymphoma is unknown but believed to be multifactorial.
The Clinical Signs of Canine Lymphoma
Our veterinarian specialists often observe these symptoms in patients that may be suffering from lymphoma:
- Enlarged lymph nodes. The ones that are usually felt first are the mandibular lymph nodes, located under the jaw.
- Decreased appetite and/or energy level.
- Coughing or hacking. This is most commonly seen after a patient gets up from sleeping, while eating or drinking, during exercise, or when getting excited. The cough or hack is usually non-productive.
- Increased drinking and urination.
- Swelling of the face or limbs (known as pitting edema). This occurs when the lymph nodes compress the vessels that normally drain fluid from the limbs or head.
- Dry, flaking skin or ulcerative skin lesions with the cutaneous form of lymphoma. Cutaneous lymphoma can also cause red lesions in the mouth or loss of pigmentation around the eyes, nose, and lips.
- Vomiting and/or diarrhea can be seen with gastrointestinal or multicentric lymphoma.
- Difficulty breathing. This can be seen with the mediastinal form due to an enlarged lymph node or from fluid accumulating in the chest (known as pleural effusion).
Diagnosing Your Pet
The gold standard for diagnosing multicentric lymphoma at our animal hospital is performing a biopsy of the lymph node. The larger the biopsy sample, the more likely we are to obtain a definitive diagnosis, and anesthesia is required to obtain a biopsy sample. For cutaneous lymphoma, a biopsy is also needed to make a diagnosis. An alternative, less invasive option is starting with a needle aspirate of the lymph node (or other affected organ). Unfortunately, a needle aspirate may not always be able to diagnose lymphoma, so a biopsy or additional testing on the aspirate sample may be warranted.
Determining the Stage of the Disease
Once we have obtained a diagnosis, staging tests may be recommended to determine the extent (stage) of disease as well as to ensure that there are no other concerns that could impact the treatment recommendations.
The Five Stages of Canine Lymphoma
- Stage I: One lymph node affected
- Stage II: Lymph nodes enlarged either in front of the diaphragm or behind it (front or back half of the body)
- Stage III: Lymph nodes enlarged on both sides of the diaphragm
- Stage IV: Liver and/or spleen involved
- Stage V: Bone marrow, eyes, intestines, skin, lungs (anywhere outside of the lymph nodes, liver and spleen) affected.
- Bloodwork with a complete blood count (CBC) and chemistry panel
- Urinalysis (with possible culture)
- Chest radiographs
- Abdominal radiographs vs abdominal ultrasound
- Typing the lymphoma:
- There are two different forms of lymphoma; B cell and T cell. B cell comprises 70-80% of diagnosed lymphoma cases, while T cell represents 20-30%. Dogs with B cell lymphoma, on average, have a longer median survival time compared to dogs with T cell lymphoma.
- Typing of lymphoma can be done on a lymph node biopsy, lymph node aspirate or blood (if there are abnormal lymphocytes in circulation).
- The tests that can type lymphoma are: flow cytometry, PARR (PCR for antigen receptor rearrangement) and immunohistochemistry.
- Bone marrow aspiration
There are a few factors regarding lymphoma, which can decrease a patient’s response as well as their median survival time (negative prognostic indicators). These include:
- Stage V lymphoma
- Substage b. This is when a patient is symptomatic for their lymphoma. It can include a decreased appetite, lethargy, vomiting and/or diarrhea.
- Substage a is when a patient is behaving normally
- Elevated calcium level (known as hypercalcemia)
- T cell lymphoma
- Prior use of long term prednisone as this can induce a resistance to some of the chemotherapy agents
Treatment for Canine Lymphoma
The most effective therapy for most types of lymphoma is chemotherapy. There are many different chemotherapy protocols available for dogs with multicentric, cutaneous and gastrointestinal lymphoma. Radiation therapy and/or surgery may also be recommended for certain types of lymphoma.
With any chemotherapy treatment, the goal is to get a patient into a complete or partial remission. Remission is when the cancer burden decreases. If the cancer becomes undetectable, then it would be considered a complete remission, which is the goal for most types of lymphomas. Partial remission means that the cancer has decreased by at least 50%.
Fortunately, most dogs tolerate chemotherapy well with less than 10% of patients needing to come into the hospital for supportive care secondary to chemotherapy side effects. Side effects can include:
- Thinning of the fur coat. Unlike people, dogs do not usually lose their fur when treated with chemotherapy, although their coat may thin out some. Exceptions include: Poodles, Old English Sheepdogs and some terriers that can lose all of their fur, but almost all dogs with have their hair growth resume once chemotherapy is completed.
- Stomach upset. This can include a picky appetite, nausea, vomiting, diarrhea and lethargy. These side effects most often occur 2-5 days after treatment, but tend to be mild and resolve on their own with some supportive medications at home within 1-2 days.
- Decrease in white blood cell counts. This is most often seen about a week after treatment. Most dogs are asymptomatic if their blood counts are low and rarely need to be placed on antibiotics or require coming into the hospital for evaluation and treatment.
Any side effects that require a visit to the hospital are considered unacceptable and may result in a reduction in the dose of the chemotherapy agent vs changing to a different chemotherapy protocol vs stopping treatment.
There may also be clinical trials available across the country which are trying to find new ways to treat lymphoma and improve our patients’ prognosis. Owners may want to inquire about this option to see if there are any clinical trials open and if their pet may be a candidate.
One of the most common questions after a patient has been diagnosed with lymphoma is whether or not they can be cured. In very rare instances, dogs are thought to be cured of their lymphoma by chemotherapy. More often, most patients will remain in remission for a certain period of time, then fall out of that remission. This is most often characterized by a recurrence of their original clinical signs. When this is seen, chemotherapy can be reinstituted and a second remission achieved, but it is usually of a shorter duration than the previous one. Eventually, most lymphomas go on to develop a resistance to all of our chemotherapy drugs, and patients must be euthanized due to a declining quality of life.
The prognosis for lymphoma is dependent on the type of lymphoma as well as the chosen chemotherapy protocol. Dogs with B cell multicentric lymphoma treated with a CHOP based protocol have a median survival time of 12-18 months. The term median implies that 50% of dogs will survive beyond this time point.
The goal with any treatment is to help to improve and maintain a patient’s quality of life. Your oncologist will be able to discuss the treatment options that are available and together you can determine what option is in your pet’s best interest. Call us today in Annapolis at (410) 224-0121.