IRF4

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IRF4

A gene on chromosome 6p25-p23 that encodes a member of the interferon regulatory transcription factor (IRF) family, which is characterised by an unique tryptophan pentad-repeat DNA-binding domain. IRF4 is lymphocyte specific and negatively regulates Toll-like-receptor (TLR)-signalling, which is central to activating the innate and adaptive immune systems.

Molecular pathology
A chromosomal translocation involving IRF4 and the IgH locus, t(6;14)(p25;q32), has been linked to myeloma.
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(21) CD138 is not helpful because it also stains a variety of carcinomas (22); therefore, MUM1 is a better plasma cell marker in this setting.23 For the distinction from breast cancer, estrogen receptor is almost always uniformly expressed in lobular breast cancer and can be a helpful diagnostic adjunct, particularly in combination with CK20 (positive in urothelial) and mammaglobin (positive in breast).
Those lymphoma cells expressed diffuse positive immunohistochemical stain for CD20, CD79a, CD5, and cyclin D1, but were negative for CD10, CD23, BCL6, and MUM1. Proliferative index (Ki-67) was about 20-30% without overt blastic change seen [Figure 3].
Immunohistochemistry describes CKAE1/AE3, Synaptophysin and CD56--negative; CD20, CD79alfa, CD3, CD5, CD30, ALK1--negative; CD10, MUM1, CD45--negative; S100 (Figure 3b), HMB45 (Figure 3c), and Melan A (MART1) (Figure 3d)--diffuse positive.
In all patients of suspicious lymphoma, paraffin sections were processed with immunochemical techniques for the demonstration of light chain restriction and the phenotypes CD20, CD79, CD10, BCL-6, c-myc, MUM1, CD3, CD43, CD5, BCL-2, cyclin D1, Ki-67, CD21 and CD23, and so on.
On immunohistochemistry, the cells were positive for CD20, Pax5, Bcl-2, MUM1, and EBERISH and negative for CD3, CD4, CD5, CD8, CD30, CD10, Bcl-6, and cyclin D1.
Immunohistochemistry of the abnormal B-cells was positive for CD20, Bcl-2, Bcl-6, MUM1, Ki-67 (at least 90%), and EBV latent membrane protein 1 (EBV LMP-1) (Figure 3).
Immunohistochemical stains of the large atypical cells were positive for CD45, CD79a, PAX5, BCL6, MUM1, OCT2, BOB1, and IgD and negative for CD30, CD15, CD10, and ALK.
Further analysis revealed positivity for BCL-6 and CD10, and negativity for MUM1, confirming a germinal center phenotype (GC type).
Immunohistochemically, the tumor was positive for leukocyte common antigen, CD20, CD79a, and multiple myeloma oncogene 1 (MUM1) but negative for CD2, CD3, CD5, CD10, CyclinD1, S-100, vimentin, desmin, and calretinin.
The neoplastic cells were positive for CD20, CD79A, MUM1, BCL6, and BCL2.