In about 5% to 10% of patients with CLL/SLL, the disease undergoes transformation to a more aggressive tumor, usually in the form of a diffuse large B-cell lymphoma (shown in this image). This phenomenon has been termed Richter Syndrome. The first manifestations are usually seen in extramedullary sites. for e.g. a rapidly enlarging mass may develop within the involved lymph node or spleen. The prognosis in this event is extremely poor with life expectancy of less than 1 year in most cases. An increased incidence of Richter syndrome has been noticed in CLL patients treated with Fludarabine. It occurs within the first year of therapy and is related to Epstein-Barr virus.