J-chain-producing immunoblastic lymphoma in a case of Richter's syndrome. Immunohistochemical evidence for a gradual malignant transformation of a single B-cell clone and flow cytophotometric data.

A 66-year old male with Richter's syndrome died 52 month after diagnosis of chronic lymphocytic leukaemia (CLL). The clinical course was characterized by a marked IgM hypoglobulinaemia which paralleled a chronically relapsing Herpes simplex infection. Autopsy showed a large retroperitoneal and intraabdominal tumour mass and well defined supradiaphragmatic lymphomas. Histological examination revealed a composite tumour consisting of CLL B-cell type (B-CLL) and immunoblastic malignant lymphoma of B-cell type (B-IbL). The lymphocytes bear mu-chains on their surface and to a lesser extend within their cytoplasm, the obviously defective immunoblasts produce J chains exclusively. Flow cytophotometric data seem to indicate an identical diploid stem line of the two tumours. The majority of the cells are in G0/1 phase. The CLL rarely produces mitoses, however, the IbL has a mitotic rate of 7% and a considerable proportion (33%) of cells in the phase of DNA-synthesis. This is the fourth malignant lymphoma and the second immunoblastic lymphoma to be reported that produces J chain in the absence of immunoglobulin.