Lymphoma is the most common tumor of the hematopoietic system in dogs. Although the abnormal cell is a blood cell, the lymphocyte, the most common form of lymphoma in dogs is multicentric disease in which many of the lymph nodes are engorged with tumor cells. The diagnosis of lymphoma is most often made off of a needle aspirate of an enlarged lymph node. It is less common to find tumor cells circulating in the blood using routine blood tests. Typically, by the time it is diagnosed, lymphoma involves multiple lymph nodes and organs in the body. Thus, treatment for this disease requires medication rather than surgery. While a combination chemotherapy protocol is considered optimal, there are many single agent treatment options for dogs with lymphoma. Patient outcome and survival depends strongly on extent of disease and clinical signs at initial diagnosis and what kind of lymphocyte is cancerous (immunophenotype of T vs B cell). Other factors that affect outcome include chemotherapy protocol used and blood calcium levels. A reasonable survival expectation for dogs with lymphoma, treated with a combination chemotherapy protocol, is 12-18 months beyond their initial diagnosis. People can be affected with Hodgkins lymphoma or non-Hodgkins lymphoma. Hodgkins lymphoma is quite rare in dogs; the canine form of disease is similar to non-Hodgkins lymphoma in people. Although immune therapies are commonly used in people with lymphoma, no such treatments have shown good efficacy in dogs. The CCOGC is collecting tissue samples from dogs with naturally occurring lymphoma because studies of lymphoma in dogs may open doorways to identify who is at risk, how to prevent the disease and how to prolong survival in or even cure all patients with this disease.