B-cell differentiation immunophenotypes in classical Hodgkin lymphomas

The bcl6/CD10/ MUM1/CD138 B-cell differentiation immunophenotypes were analysed in 101 cases of classical Hodgkin lymphomas (cHL) aiming to elucidate their histogenesis. Three major bcl6/CD10/MUM1/CD138 immunophenotypes were distinguished on the basis of the immunohistochemical positivity of Hodgkin and Reed-Sternberg (H/RS) cells: (a) the late germinal center (GC)/ early post-GCB-cell-like immunophenotype (bcl6-/CD10-/MUM1+/CD138-); 59/101 cases (59%), ( b) the post-GCB-cell-like immunophenotype (bcl6-/CD107/MUM1+/CD138+); 24/101 cases (24%) and (c) the indeterminate immunophenotype (bcl6+/ CD107/MUM1+/CD138-: 14 cases and bcl6+/CD107/ MUM1+/CD138+: four cases); 18/ 101 cases (18%). The above findings indicate that H/ RS cells in most cHL display bcl6/CD10/MUM1/CD138 immunophenotypes consistent with late GC/early post-GC or post-GCB-cell differentiation. In addition, H/ RS cells in a small fraction of cHL display indeterminate bcl6/CD10/MUM1/CD138 immunophenotypic profiles which are characterized by simultaneous expression of GC, late GC/early post-GC and post-GCB-cell differentiation proteins. These immunophenotypic profiles do not correspond to the differentiation immunophenotypes of normal B-cells and their identification in a part of cHL suggests that the differentiation process of H/RS cells is not complete in a fraction of these cells and/or is still ongoing at the time of observation.