Malignant Lymphoma in Dogs
Canine malignant lymphoma, also called lymphosarcoma, is the most common cancer that occurs in dogs. The exact cause of the disease is unknown, but both genetics and environment are thought to be factors in the disease that affects the lymphocytes, important parts of the immune system.
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Basics
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While lymphoma may affect any breed of dog, there are breeds in which this cancer is more common, including golden retrievers, Rottweilers, pit bulls, German shepherds, poodles, boxers, Scottish terriers, beagles and basset hounds.
Lymphosarcoma is a progressive, fatal disease that many times arises from cancerous formation in lymphoid cells in the lymph nodes, bone marrow, thymus and spleen, according to the Merck Veterinary Manual.
There is no cure for this disease, but veterinarians have achieved some success in extending life with chemotherapy, radiation and/or surgery, depending on the type and severity of the lymphoma.
Types
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The symptoms associated with canine malignant lymphoma will depend partially on what system or organs of the dog are affected. There are four types of this disease, named for the anatomical parts of origin: multicentric, alimentary, mediastinal and extranodal. Of the four, multicentric is the most prevalent, diagnosed in about 80 percent of dogs with the disease, according to the Merck Manual.
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Multicentric Symptoms
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An early sign is the fast and non-painful growth or generalized swelling of the animal's lymph nodes. A dog's lymph nodes may be found under the jaw, in the front of the chest, at the top of the front legs, at the inner curve of the back legs, and at the top of the back legs where they meet the hip.
Other outward symptoms may not be noted until later in the disease, when damage to internal organs by the lymphoma has occurred. At that time, the dog may be lethargic, feverish, depressed, weak and/or experience loss of appetite.
Alimentary Symptoms
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This type of lymphoma is diagnosed less than 10 percent of the time. In this form, it is the dog's digestive system that is the focal area of the disease. Symptoms such as vomiting, abdominal pain, diarrhea and loss of appetite may be present. The dog will lose a large amount of weight due to his inability to properly digest and absorb food due to the disease.
Mediastinal Symptoms
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Often there are no early warning signs of this type of lymphoma, one of the more rarely occurring types of this disease. What may first be noticed is the dog having difficulty breathing, which may also result in lethargy and weakness. Other signs that may be present is the dog drinking large quantities of water and urinating frequently.
Extranodal Symptoms
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In this type of lymphosarcoma, the disease may be present in a number of areas, including the skin, where a single raised nodule of ulcerated skin or many scaly lesions scattered on the animal's body may be present. There may be difficulty breathing if the lungs are involved, kidney failure if the kidneys are involved, blindness if the eyes are affected and/or seizures if the disease has affected the central nervous system.
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