Reclassification of diffuse large B cell lymphoma to large B cell lymphoma with IRF4 rearrangement in an adult population

Aims Large B cell lymphoma with IRF4 rearrangement (LBCL‐IRF4) is a new entity in the 2017 revised World Health Organisation (WHO) classification that was initially mainly reported in children. After identification of a 79‐year‐old patient, we assessed how often IRF4 rearrangements can be detected in adult diffuse large B cell lymphomas (DLBCLs) which have to be reclassified to LBCL‐IRF4 based on fluorescence in‐situ hybridisation (FISH) for IRF4. Methods and results With FISH, we studied the presence of IRF4 rearrangements in 238 lymphomas that were diagnosed as DLBCL according to the previous WHO classification of 2008. Conclusions In addition to the index patient, an IRF4 rearrangement was detected in another five of 237 patients (2%). The immunohistochemical profile of these five IRF4 rearranged lymphomas was consistent with previous reports of LBCL‐IRF4. One case was recognised to represent transformation of follicular lymphoma rather than de‐novo LBCL‐IRF4. BCL6 rearrangements were found in two cases of LBCL‐IRF4; BCL2 and MYC rearrangements were excluded. Patients presented with limited stage disease with involvement of the head and neck in three patients, and involvement of the lung and thyroid in two others. This study shows that, although rare, LBCL‐IRF4 should also be considered in older patients and at localisations other than the head and neck region.