Hodgkin's disease variant of Richter's syndrome clonally related to chronic lymphocytic leukemia arises in ZAP-70 negative mutated CLL

Abstract

Chronic lymphocytic leukemia (CLL) may derive from either immunoglobulin V(H) gene unmutated (naïve) or mutated (antigen-experienced) post-germinal center B-cells. Richter's syndrome denotes the transformation of CLL into aggressive B-cell lymphoma. Most Richter's syndrome cases are secondary diffuse large B-cell lymphomas, but some are Hodgkin's disease variants. Hodgkin's lymphoma is thought to originate from germinal center or post-germinal center B-cells with evidence of somatic V(H) hypermutation. Taking into account CLL and Hodgkin's lymphoma histogenesis, hypothetically only CLL derived from V(H) mutated B-cells can clonally progress to Hodgkin's lymphoma variant of Richter's syndrome. To test our hypothesis, we analyzed the CLL ZAP-70 status as a surrogate for the V(H) mutational status in four patients with subsequent Hodgkin's disease variants of Richter's syndrome. In all three cases with proven or suspected clonal relationship between Hodgkin and Reed-Sternberg- and leukemia cells, the CLL samples remained negative for ZAP-70, corresponding to CLL histogenesis from V(H) mutated B-cells. These empirical data suggest that the histological and clinical diversity of Richter's transformation could be to a part explained by the different origin of CLL, with Hodgkin's disease variants arising probably only in V(H) mutated CLL.