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Lymphoma in Dogs

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    Lymphoma in Dogs

    (The information contained on this page is in no way intended to replace the advice of your personal veterinarian.)

    Lymphoma is one of the most common cancers seen in dogs. Although there are breeds that appear to be at increased risk for this disease, lymphoma can affect any dog of any breed at any age. It accounts for 10-20% of all cancers in dogs.

    Lymphoma (lymphosarcoma or non-Hodgkin’s lymphoma) is a malignant cancer that involves the lymphoid system. In a healthy animal, the lymphoid system is an important part of the body’s immune system defense against infectious agents such as viruses and bacteria. Lymphoid tissue normally is found in many different parts of the body including lymph nodes, liver, spleen, gastrointestinal tract and skin. Lymphosarcoma is classified according to the location in the body in which the cancer begins.

    These include:

    • Multicentric form occurs in the lymph nodes.
    • Gastrointestinal form occurs in the stomach, intestines, liver and lymph nodes in the abdomen.
    • Mediastinal form occurs in the mediastinum, in front of the heart in an organ called the thymus. Hence this form of lymphosarcoma sometimes is called thymic lymphoma.
    • Cutaneous form occurs in the skin.
    • Acute lymphoblastic leukemia occurs when the disease starts in the bone marrow.
    • Miscellaneous forms of lymphosarcoma are less common and include those that begin in the nervous system, nasal cavity or kidneys.

    While we understand how lymphomas form, we still do not understand why. There is speculation that environmental factors such as exposure to pesticides (especially herbicide 2,3-D) or strong magnetic fields increase the incidence, but there is currently no strong proof of this. There is also some evidence of a possible genetic correlation, but further studies need to be performed to determine the exact risk factors involved in canine lymphoma.

    Risk Factors
    Lymphosarcoma occurs in middle-aged to older dogs. In fact, most affected dogs are between 5-9 years of age. Certain breeds of dogs have a higher than average risk of developing this disease and include Rottweilers, Scottish terriers, Golden retrievers, Basset hounds, and German shepherds. Males and females are affected equally. In dogs, there may be a genetic basis for this disease and, in certain breeds, some families several closely related animals have been affected.

    Most of the time, lymphoma appears as “swollen glands” (lymph nodes) that can be seen or felt under the neck, in front of the shoulders, or behind the knee. Occasionally, lymphoma can affect lymph nodes that are not visible or palpable from outside the body, such as those inside the chest or in the abdomen. Other symptoms include vomiting, diarrhea, loss of appetite, weight loss, lethargy, difficulty breathing and increased thirst or urinations. Cutaneous lymphosarcoma can cause redness or flakiness of the skin, ulceration (especially near the lips and on the footpads), itchiness or lumps in the skin. Clinical signs will vary depending on the stage of the disease, volume of tumor and anatomic location of the lymphoma.

    If the patient is hypercalcemic, assess kidney function, and determine if the dog has normal neutrophil and platelet counts so that chemotherapy can safely be administered. Lymphoma can also be diagnosed with x-rays and ultrasound. The exact tests performed will depend on the location of the tumor.

    Once a diagnosis of lymphoma has been established, it is necessary that the cancer be staged. Staging is the process by which the veterinarian determines to what extent the lymphoma has spread throughout the animal’s body. The degree of spread affects the manner in which a dog is treated.

    Stage Definition
    Stage I – Involvement of a solitary lymph node or lymphoid tissue in a single organ
    Stage II – Several lymph nodes in the same general area involved
    Stage III – All peripheral lymph nodes involved
    Stage IV – Involvement of liver and/or spleen, and/or anterior mediastinum in the chest involved
    Stage V – Involvement of bone marrow (some classifications consider cutaneous involvement in this stage)

    Substage a – without systemic signs of disease (patient generally has no symptoms)
    Substage b – with systemic signs of disease (patient does not feel well)

    The chemotherapy treatment usually consists of a combination of oral and injectable drugs given on a frequent basis. The exact treatment protocol will vary depending on the veterinarian and financial resources of the dog’s family. Below are some common protocols available for treatment after the initial diagnosis of lymphoma.

    Multi-drug protocol: Treatment consists of the use of several chemotherapy drugs (prednisone, L-asparaginase [elspar], vincristine, cyclophosphamide [cytoxan] and doxorubicin [adriamycin]). Weekly chemotherapy treatments are given for approximately 8 weeks. The treatments are then spaced to every 2 weeks to complete a total of 6 months of treatment. The average survival time for patients with stage IIIa or IVa lymphoma treated with this protocol is 1 and 1/2 years.

    Doxorubicin alone: The patient is treated with a total of 5 treatments of doxorubicin at
    3-week intervals. The average survival time with this approach is 10-11 months.

    COP: This protocol involves a combination of cyclophosphamide in tablet form, vincristine and prednisone. 4 weekly intravenous injections of vincristine are given, followed by injections at 3-week intervals to complete 6 months of treatment. Cyclophosphamide is given over 4 days every 3 weeks (4 days on; 17 days off). Prednisone is given daily for 6 months. The average survival time with this protocol is reported as 8-10 months.

    Prednisone alone: This medication is a steroid and can be given in pill form daily at home. The average survival time for patients with lymphoma treated with prednisone only is 60 days.

    Some owners choose not to treat dogs that develop lymphoma. The life expectancy of these untreated dogs averages 4 to 6 weeks. Oral prednisone therapy may reduce the swellings and discomfort, but probably will not appreciably extend their life span. It must also be noted that oral prednisone treatment prior to chemotherapy is not recommended and may actually reduce the effectiveness of the chemotherapy.

    In dogs that do undergo one of the recommended chemotherapy protocols, life expectancy can be extended. Most dogs with lymphoma develop medium to high-grade lymphoma that is very responsive to chemotherapy. Greater than 75% of dogs with lymphoma are expected to achieve a complete remission with chemotherapy. The duration of the first remission is variable, depending on the chemotherapy protocol used, with median remission times varying from 6 months to 11 months. The second remission is more difficult to achieve, with approximately 40% of dogs with lymphoma achieving complete remission with a second course of chemotherapy. Less than 20% of dogs with lymphoma will achieve a third complete remission. Approximately 40-45% of dogs with lymphoma live one year with treatment. Less than 20% of dogs with lymphoma live 2 years with treatment. Eventually, the cancer will infiltrate an organ to such an extent that organ fails (often this is the bone marrow or the liver). The patient loses his/her appetite, vomits or gets diarrhea, weakens and dies. At some point the tumor becomes resistant to therapy and no further remissions can be obtained.

    However, if a dog tolerates chemotherapy (fortunately most dogs do) their quality of life can be quite good during the treatment period. Treatment for lymphoma in the dog is considered one of the more successful cancer treatments and can often be performed by a local veterinarian without the need to travel long distances to veterinary schools or specialty clinics. It helps to remember that one year can equate to almost 10% of a dog’s expected life span, therefore, the increased life expectancy with lymphoma treatment is often well worth it.

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