Richters transformation
Richters syndrome (RS), also known as Richters transformation, is a transformation of B cell chronic lymphocytic leukemia (CLL) or hairy cell leukemia into a fast-growing diffuse large B cell lymphoma, a variety of non-Hodgkin lymphoma which is refractory to treatment and carries a bad prognosis.  There is also a less common variant in which the CLL changes into a Hodgkins lymphoma. Rarely, transformations to a form of myeloid leukemia have been observed. These extraordinarily rare transformations carry a very poor prognosis.
Richters transformation affects about 5% of CLL patients at some point during their lives.

Signs and symptoms
Symptoms of Richter’s transformation in a CLL patient include fever (without infection), elevated serum levels of lactate dehydrogenase, and rapidly enlarging lymph nodes.  While about 8% of all CLL patients will have elevated levels of serum lactate dehydrogenase (LDH), more than 50% of CLL patients with Richters transformation will have elevated LDH levels.Richters can appear suddenly, even in patients who were in remission.

Cause
A case of RS may have arisen by one of two different routes:  a transformation of the CLL cells into lymphoma, or the appearance of an unrelated lymphoma.It is thought that genetic defects may introduce the additional abnormalities necessary to transform CLL cells into Richters syndrome cells.

Treatment
Treatment with conventional immunochemotherapy is usually indicated; in younger patients, allogeneic bone marrow transplantation may be curative.

Prognosis
The prognosis is generally poor.  The RS score (Richter syndrome score), which is an estimate of the patients prognosis, is based on the patients performance status, LDH, platelet count, the size of the lymphoma tumors, and the number of prior therapies already received.  Overall, the median survival is between five and eight months.  Untreated, RS is invariably fatal.
The Hodgkins lymphoma variant of Richters carries a better prognosis than the predominant diffuse large B-cell lymphoma type, but a worse prognosis than a de novo case of Hodgkins.

Epidemiology
A SEER-based analysis estimated the risk of Richters transformation in Chronic Lymphocytic Leukemia (CLL) patients in the United States to be about 0.72%. The majority of transformations (85%) were Diffuse Large B-Cell Lymphoma (DLBCL), while transformation to Hodgkin occurred in 15% of cases. Most of those transformation events were nodal (74%). The most commonly involved extra-nodal sites were the GI tract (25%), skeletal system (19%), and the brain/CNS (12%). The median time from the diagnosis of CLL to the development of Richters transformation was about 4 years, with no significant difference in the time interval based on histology of the transformation event comparing DLBCL and Hodgkins. The median age at the time of Richters transformation was 66 years.

References
Further reading
Tsimberidou AM, OBrien S, Khouri I, Giles FJ, Kantarjian HM, Champlin R, Wen S, Do KA, Smith SC, Lerner S, Freireich EJ, Keating MJ (May 20, 2006). "Clinical Outcomes and Prognostic Factors in Patients With Richters Syndrome Treated With Chemotherapy or Chemoimmunotherapy With or Without Stem-Cell Transplantation". Journal of Clinical Oncology. 24 (15): 2343–2351. doi:10.1200/JCO.2005.05.0187. PMID 16710033. S2CID 25490586.