Lymphoma (lymphosarcoma) is a relatively common type of cancer found in dogs and cats which arises from lymphoid tissue. Lymphocytes are present to detect and mount immune responses to invading organisms. They can be found in tissues all over the body, meaning lymphoma can affect almost any organ, but 80% of the time it is found in the external lymph nodes. On average about 18 out of every 100,000 dogs develop lymphoma, and in dogs over 10 years of age it is as high as 84/100,000. Middle aged dogs are most commonly affected, but dogs less than a year of age can be affected as well. Any breed can be affected, but Golden Retrievers seem to have an increased incidence. The cause is unknown. Depending on the organ system affected, clinical signs can vary. Many dogs with only external lymph node involvement can present with no signs other than enlarged lymph nodes. Others can experience weight loss, vomiting, diarrhea, and lethargy.
Fortunately, Lymphoma is one of the few types of cancer in dogs that can respond well to chemotherapy. Although cures are infrequent, significant remission and survival times can be achieved with minimal to no side effects in most patients. The goal of treatment is to extend the amount of GOOD QUALITY time for the patient. Dogs do not lose their hair like humans do, although coat changes can occur in certain breeds. In general, when side effects do occur, they are usually limited to either vomiting or diarrhea in the first few days after treatment, or bone marrow suppression, low white blood cell counts, and susceptibility to infection about a week after treatment. Most of these side effects are infrequent and transient.
The stage of the disease has bearing on the prognosis with treatment. Patients are staged 1-5, with a subcategory of a or b (not sick, or sick). Stage 1 & 2 refer to one lymph node, or two in a respectively, but this is a very rare presentation. Stage 3 is when multiple lymph nodes are enlarged and is the most common presentation. Stage 4 denotes involvement of the liver and spleen, and Stage 5 means there is bone marrow or other organ system involvement. The lower the stage, the better the prognosis for longer survival times. Older dogs do just as well as younger dogs in treatment – age is not a disease! Intestinal lymphoma tends to carry a worse prognosis and shorter survival times in most cases.
We use the Madison (or University of Wisconsin) protocol which lasts for 25 weeks. There are a total of 13 in hospital treatments with this protocol and some medications will be given at home. On average, 90% of dogs will go into remission with this protocol. Average remission time is approximately 9-10 months including the 25 weeks of treatment). Half of these dogs will be alive with good quality at 1 year, and 25% will achieve 1.5 years or more. After a relapse, 50% of dogs will go back into remission with second protocol, but second remissions are often shorter. The drugs involved include vincristine, cyclophosphamide, doxorubicin, chlorambucil and prednisone. Left untreated, most dogs will succumb to the disease within a month of diagnosis.
Author: Dana Brooks, DVM, Diplomate ACVIM
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