Lymphoma or lymphosarcoma is a cancerous disease of lymphocytes, a particular form of white blood cells that originate in lymph nodes and bone marrow. Unlike leukemia, where the cancerous white blood cells remain in the bloodstream, lymphoma is a solid tissue tumor of the node(s) itself. The lymphoma cells can migrate to other lymph nodes and to major organs. In other words, it is capable of metastasizing. To better understand lymphoma, one needs to understand how white blood cells originate. They are derived from a parent or stem cell. This stem cell is the origin of all white blood cells. In the case of lymphoma, something goes wrong during the process of differentiation of the lymphocytes. There are several different types of lymphocytes. Some are called B-cells (Bursa cells) which produce antibodies and some are called T-cells (Thymus cells) which signal additional chemical defenses of the body to ward off an infectious attack. A lymphoma of T-cell origin will have a poorer prognosis and will often have an associated high calcium level in the blood. At this time, tests to determine whether the lymphoma is B- or T-cell mediated are not readily available. An intriguing area of study is that of retroviruses that might play a part in the development of lymphoma. Although, there is no proof that a virus causes this disease in the dog, viruses have been implicated in certain types of lymphoma of cats, birds, rodents and humans. Until we know more about this disease, we can only say that its exact origin in dogs is yet unknown and both forms, B- and T-cell, are sufficiently deadly and will be considered as one entity for the purposes of this discussion. We do know that lymphoma can affect dogs at any age, but it is most often seen in dogs between the ages of 5 and 9. It is equally distributed between the sexes and it is one of the most common cancers of the dog. Familial lymphoma occurs in Saint Bernards, but has not been proven in other breeds.
One of the most common signs is the enlargement of lymph nodes that the owner can actually feel and is one of reasons for the first seeking of treatment. Other nonspecific signs include: lethargy, weakness, loss of appetite, weight loss, diarrhea, shortness of breath, difficulty swallowing, increased thirst or increased urination. Other symptoms may be evident depending on what organ or organs the lymphoma has spread to and the degree of hypercalcemia. The liver, spleen, kidneys, lungs, intestinal tract, bone marrow, central nervous system and skin can all be affected.
Physical exam includes palpation of lymph nodes and abdominal organs, examination of the oral mucous membranes for pallor (anemia from bone marrow involvement), membranes of the eye (discoloration might be due to liver or kidney involvement), and rectal palpation to feel for additional lymph nodes. Commonly ordered tests include: complete blood count, serum chemistry, urinalysis and possibly chest and abdominal x-rays or ultrasound. Abnormalities that might be seen in the CBC include: a decrease in red blood cells and platelets and an elevated white blood count. The chemistry might show a high calcium level because the malignant cells trigger a substance that causes bone breakdown which releases calcium into the bloodstream. Liver enzymes and the BUN and creatinine might be elevated if there is liver and or kidney involvement. Protein and albumin levels may be low if the liver is affected and unable to produce these as usual. Bone marrow aspiration is a common diagnostic procedure for lymphoma as well. If found in the bone marrow, this means that the disease has definitely metastasized and has reached an advanced stage. Although all of the above tests and exams help to determine presence of disease, the only way to absolutely diagnose and stage lymphoma is by biopsy.
The mainstay treatment of lymphoma is combination chemotherapy in which a variety of drugs are given according to a specific plan or protocol. Many chemotherapy protocols exist and they are ever-changing. Commonly, prednisone, a steroid drug will be given alone or in conjunction with other chemotherapy drugs to decrease the inflammation that occurs in the dog’s body due to the action of the disease or the effect of the chemotherapy. A word of caution is offered here and that is if you decide not to proceed with chemotherapy and to use prednisone alone and later decide to begin chemotherapy, the chemotherapy will be less effective because of the initial prednisone use.
Treatment is aimed at remission of disease. Without treatment, dogs on average will live 30 days; if placed on prednisone alone, several weeks may be added to this. Chemotherapy can provide a remission of up to 2 years, but beyond that, survival is not expected because lymphoma has a high propensity for recurrence and when this happens, it is more resistant to chemotherapy drugs. Lymphoma can be staged in order to offer a better idea of prognosis:
Stage I: Lymphoma affects one to no lymph nodes.
Stage II: Nodes are affected but they are contained to one area of the dog’s body.
Stage III: Lymph nodes throughout the body are affected.
Stage IV: Liver and spleen also affected.
Stage V: Blood, bone marrow, organs or the central nervous system are affected.
There are also two sub-stages:
- No clinical signs and symptoms are present.
- Clinical signs and symptoms are present.
Immunophenotyping (not readily available) can further differentiate lymphoma into two categories: B-cell or T-cell. The latter has the poorer prognosis.
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