A low-grade B-cell lymphoma with prolymphocytic/paraimmunoblastic proliferation and IRF4 rearrangement

B cell lymphoma with IRF4 rearrangement: A clinicopathological study of 13 cases

Interferon regulatory factor 4 (IRF4) rearrangement is commonly detected in patients with a range of lymphoproliferative malignancies, including myelomas, large B cell lymphomas and low-grade B cell neoplasms. However, IRF4 rearrangement is generally a relatively rare finding in these latter two cancer types. In the present article, we describe and summarize the clinicopathological and genetic features of 13 cases of B cell lymphoma with IRF4 rearrangement, including 12 cases of large B cell lymphoma and one case of low-grade lymphoma exhibiting such rearrangement. These cases were detected in six females and seven males between 14 and 71 years of age. From a morphological perspective, large B cell lymphoma tumors included in this analysis exhibited large neoplastic cells in diffuse or follicular patterns, while the case of low-grade lymphoma mainly composed of small lymphocytes. All analyzed cases exhibited a split in the IRF4 gene consistent with IRF4 translocation. Three of six analyzed large B cell lymphoma cases harbored IGLL5 mutations. Mutations in SAMHD1 were detected in the low-grade lymphoma with IRF4 rearrangement case. In summary, our results offer further insight into the morphological and molecular heterogeneity of cases of B cell lymphoma exhibiting IRF4 rearrangements.

Primary Low-Grade B-Cell Lymphoma of Skull With Translocation Between Immunoglobulin and Interferon Regulatory Factor 4 Genes

Low-grade B-cell lymphoma with immunoglobulin ( IG) and interferon regulatory factor 4 ( IRF4) gene rearrangement is extremely rare, with only 4 cases being previously reported. In this article, we report one additional case that arises from the skull and review the literature. The patient was a 69-year-old man who presented with recurrent and disabling vertigo and was found to have a 5.0 × 1.7 cm lesion within the left posterior parietal bone. Histological examination revealed a bone lesion with diffuse lymphoid infiltrate comprising of mostly small lymphocytes with scant cytoplasm, slightly irregular nuclei and inconspicuous nucleoli, and scattered larger cells resembling prolymphocytes and paraimmunoblasts. Immunohistochemical studies showed that the neoplastic cells were positive for CD20, CD79a, PAX5, CD23, CD43, BCL-2, BCL-6, MUM-1, LEF-1, and IgM and negative for CD5, CD10, cyclinD1, SOX11, and IgD. Flow cytometric analysis identified CD5 negative and CD10 negative monoclonal B cells with lambda light chain restriction. Fluorescence in situ hybridization analysis revealed del(13q) abnormality, but was negative for IGH/BCL2, IGH/CCND1, and BIRC3/MALT1 translocations. Next-generation sequencing identified IGK-IRF4 rearrangement and BRD4 E1113 del abnormalities. Given a low clinical stage (IE) of the disease, the patient did not receive additional treatments and was free of disease at 1 year after the diagnosis.

Pathology of indolent B-cell neoplasms other than follicular lymphoma

Indolent B-cell lymphomas include follicular lymphoma (FL), chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) and marginal zone lymphomas (MZLs). They are a diverse group of disorders with different clinical, morphological, immunophenotypic and genetic features. However, because of several histological similarities, such as in cell size and nodular structure, it may sometimes be difficult to differentiate them and to make a definitive diagnosis. In this review article, we summarize the histopathology of indolent B-cell neoplasms excluding FL and including hairy cell leukemia, and briefly mention recent genetic findings useful for their differential diagnosis. In addition, a provisional subtype of low-grade B-cell lymphoma, "prolymphocytic/paraimmunoblastic lymphoma", is described.