Lymphoma is a cancer of white blood cells called lymphocytes, which are a key part of the immune system. In multicentric B-cell lymphoma, the malignant cells are B-lymphocytes — the type normally responsible for producing antibodies. The disease typically causes rapid, painless enlargement of lymph nodes throughout the body, which is why it is called 'multicentric.' It is the most common blood-cell cancer in dogs and one of the most frequently diagnosed canine cancers overall. Without treatment, the disease progresses quickly, with a typical survival of just four to six weeks. With chemotherapy, however, most dogs achieve remission, and the B-cell subtype generally responds better to treatment and carries a more favourable prognosis than T-cell lymphoma. Certain breeds, including Golden Retrievers, Boxers, and Bernese Mountain Dogs, are more frequently affected.