Large B-cell Lymphoma with IRF4 rearrangement: a pitfall in the pathological diagnosis of lymphoma

Background: Large B-cell lymphoma (LBCL) with interferon regulatory factor 4 (IRF4) rearrangement (IRF4+LBCL) is a rare and newly discovered subtype of mature B cell neoplasms. Case presentation Here, we describe a patient of 32 years old who was diagnosed IRF4+LBCL. Histological examination showed the normal structure of the lymphoid tissues were destroyed, and slightly crowded follicular or nodal structures instead. There were obvious necrosis on the surface of tonsil and the central part of some follicles. The monomorphic atypical lymphoid cells proliferated and grew consistently, which were of medium size or large, and the nuclear chromatin was opening. Some tumor cells can be seen around the normal striated muscle tissues near the tonsils. Immunohistochemistry (IHC) could show that CD20, CD79a, MUM-1 and BCL6 were positive, Ki-67 was 80%; CD3, CD5, CD10, BCL2, CD30, CD56, CD99, CD38, and CD138 were negative. In situ hybridization (ISH) of EBER was negative. Fluorescence in situ hybridization (FISH) confirmed that IRF4 gene rearrangement was found in tumor cells. The patient was followed up for 18 months without tumor after chemotherapy. Conclusion Generally speaking, destructive growth patterns with a large number of necrosis, high proliferation index and so on all suggest that the tumor is highly invasive. And in terms of pathological morphology, IRF4+LBCL can be similar to both high-grade follicular lymphoma (FL) and diffuse large B-cell lymphoma (DLBCL). But actually this disease is indolent and significantly different.