Cytogenetic evidence for the clonal nature of Richter's syndrome.

Sequential chromosome studies were done on a patient who developed diffuse histiocytic lymphoma (DHL) after a long history of untreated chronic T-cell leukemia. During the indolent phase of her disease, a pseudodiploid lymphocyte population with 3q+ and 14q+ chromosome markers gradually replaced the originally diploid tumor cells. The karyotype of the lymphoma was hypertriploid (70--74 chromosomes) with the same 3q+ and 14q+ markers. The findings indicate that DHL in this patient evolved from the leukemic T-cell clone.