Lymphoma is a common cancer of middle-aged and older dogs. It is a cancer of the white blood cells known as lymphocytes, of which there are two main types: B cells and T cells. Lymphoma may originate in any lymph tissue, including the lymph nodes, spleen, liver, bone marrow and thymus. Lymphosarcoma, a type of lymphoma, may also affect the skin, eyes, central nervous system, gastrointestinal tract, liver and lungs. It is the most common cancer in dogs. This cancer can be aggressive if left untreated, but it often responds favorably to chemotherapy, adding months and sometimes years to the pet's life. Even though this is a common cancer in people and dogs, it is not known why it develops. A genetic predisposition may exist because certain breeds, such as the golden retriever, seem prone to the disease.
Clinical signs depend on the area of the body affected. Widespread enlargement of the lymph nodes may be the only sign in dogs with the common, multi-centric form of lymphoma. Other forms of lymphosarcoma may cause skin lumps, sudden blindness, seizures, back pain, or shortness of breath.
Diagnosis of lymphoma requires certain testing, including a blood test, a fine needle aspirate of lymph nodes, and X-rays and/or an ultrasound to evaluate internal organ involvement. Specialized testing to determine the type of lymphoma (B-cell versus T-cell) is also necessary to determine proper therapy.