Lymphoma In Dogs
Lymphoma in dogs is a malignant cancer originating from lymphocytes, which are an important component of the immune system. Lymphoma also occurs in humans. The disease occurs in lymph nodes, bone marrow, and organs such as the liver, spleen, eye, skin, and gastrointestinal system. It is also known as lymphosarcoma.
Lymphoma is one of the most common malignant tumors to occur in dogs. The cause is genetic, but there also suspected environmental factors involved.
Lymphoma in dogs usually affects breeds such as a, Boxer, Scottish Terrier,Basset Hound, Airedale Terrier, Chow Chow, German Shepherd,Poodle,St. Bernard ,English Bulldog,Beagle, and Golden Retriever
The cancer is classified into low and high grade types. Classification is also based on location. The four location types are multicentric, mediastinal, gastrointestinal, and extranodal (involving the kidney, central nervous system, skin, heart, or eye). Multicentric lymphoma, the most common type, is found in the lymph nodes, with or without involvement in the liver, spleen, or bone marrow. Mediastinal lymphoma occurs in the lymph nodes in that area and possibly the thymus. Gastrointestinal lymphoma occurs as either a solitary tumor or diffuse invasion of the stomach or intestines, with or without involvement in the surrounding lymph nodes, liver or spleen. Classification is further based on involvement of B-lymphocytes or T-lymphocytes.
General symptoms of lymphoma may include depression, fever, weight loss, loss of appetite, and vomiting. Hypercalcemia (high blood calcium levels) occurs in some cases of lymphoma, and can lead to the above symptoms plus increased water drinking, increased urination, and arrhythmias.
Multicentric lymphoma presents as painless enlargement of the peripheral lymph nodes. This is seen in areas such as under the jaw, the armpits, the groin, and behind the knees. Enlargement of the liver and spleen causes the abdomen to distend. Mediastinal lymphoma can cause fluid to collect around the lungs, leading to coughing and difficulty breathing. Hypercalcemia is most commonly associated with this type. Gastrointestinal lymphoma causes vomiting, diarrhea, and melena (digested blood in the stool).
Lymphoma of the skin is an uncommon occurrence. An important type originating from T-lymphocytes is mycosis fungoides. It can have a wide variety of appearances, from a single lump to large areas of bruised, ulcerated, hairless skin.
Symptoms for lymphoma in other sites depend on the location. Central nervous system involvement can cause seizures or paralysis. Eye involvement, seen in 20 - 25 % of cases, can lead to glaucoma, uveitis, bleeding within the eye, retinal detachment, and blindness. Lymphoma in the bone marrow causes anemia, low platelet count, and low white blood cell count.
Biopsy of affected lymph nodes or organs confirm the diagnosis. X-rays, ultrasound, blood analysis, amd bone marrow biopsy reveal other locations of the cancer. The stage of the disease is important to treatment and prognosis.
Stage I - only one lymph node or lymphoid tissue in one organ involved.
Stage II - lymph nodes in only one area of the body involved.
Stage III - generalized lymph node involvement.
Stage IV - any of the above with liver or spleen involvement.
Stage V - any of the above with blood or bone marrow involvement
Each stage is divided into those with systemic symptoms (loss of appetite, weight loss, etc.) and those without.
A complete cure is rare with lymphoma, but long remission times are possible with chemotherapy. With effective protocols, average first remission times are 6 to 8 months. Second remissions are shorter and harder to accomplish. Average survival is 9 to 12 months. The most common treatment is a combination of cyclophosphamide, vincristine, prednisone, L-asparaginase, and doxorubicin.
Other chemotherapy drugs such as chlorambucil, lomustine (CCNU), cytosine arabinoside, and mitoxantrone are sometimes used in the treatment of lymphoma by themselves or in substitution for other drugs. In most cases, appropriate treatment protocols cause few side effects, but white blood cell counts must be monitored.
When cost is a factor, prednisone used alone can improve the symptoms dramatically, but it does not significantly affect the survival rate. The average survival times of dogs treated with prednisone and untreated dogs are both one to two months. Using prednisone alone can cause the cancer to become resistant to other chemotherapy agents, so it should only be used if there is definitely no chance of further treatment.
Lymphoma with a histologic high grade generally respond better to treatment. Dogs with B-lymphocyte tumors have a longer survival time than T-lymphocyte tumors. Mediastinal lymphoma has a poorer prognosis than other types, especially those with hypercalcemia. Otherwise, the stage of the disease is the best prognostic factor.
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