Fig. 5.

Histologic and immunophenotypic features of large B-cell lymphoma with IRF4-rearrangement presenting in the tonsil. Case LYWS-1279 courtesy of R. Mariani. A Panoramic view of a tonsil showing residual normal tonsil areas and lymphoma infiltration with follicular and diffuse pattern. B Higher magnification shows a lymphoid infiltrate composed of large-sized centroblasts. C IRF4/MUM1 stain shows in the normal residual lymphoid tissue few positive plasma cells. The left side shows a follicular growth pattern whereas the left side reveals a diffuse growth pattern. D The tumor cells show an aberrant CD5 expression. Note the strong CD5 expression of the reactive T cells. E The tumor cells are positive for BCL6, and F BCL2. G The MIB1 stain shows the normal polarization of residual germinal centers, whereas the tumor shows a proliferation of approximately 80% in both the follicular and in the diffuse areas. H The CD10 stain is strong and homogeneous positive in the residual germinal center whereas the stain is weak in the follicular areas and partially lost in the diffuse areas. I IGV screenshots of chimeric pairs in chromosomes 6 and 14 supporting the presence of IGH::IRF4 juxtaposition