IRF4 and B-cell non-Hodgkin lymphoma: When MUM1/IRF4 is strongly expressed, FISH analysis for IRF4 is required to exclude large B-cell lymphoma with IRF4 rearrangement; and (3) FL with uncommon features comprising FL with “blastoid” or “large centrocyte” features characterized by high proliferative index, and MUM1/IRF4 expression [57] that needs to be distinguished from large B-cell lymphoma with IRF4 rearrangement [58].